Ive decided to rewire my truck after some strange issues and throwing money at it for a few weeks.

If anyone has completely rewired one of these and has (or could draw) a simple wire diagram of what you did, it would be helpful. I cant find a good one online.

To simplify the truck and for me to understand my system I would like to wire up separate circuits and harnesses, it seems like everything is somehow interconnected and it's just too confusing. What i mean by that is have maybe 3 or more separate harnesses and diagrams. #1 for the vitals (starter, ignition system, alternator, electric choke, fuel pump). #2 for lights( hi/low beam, tail/brake lights, hazards). And #3 for accesories (wipers, horn, radio, blower fan, cigarette lighter ect). Could there be an issue wireing this truck with all separate circuits?

But I'd like to just focus on #1 for now and just get the truck running, and add in the other stuff later.

So im running a GM ignition module, a GM 3 wire alternator(60A), Mr gasket 12v fuel pump. Here is a wire diagram that I drew up:






(sorry, it looks like a 5 year old drew this)

This should start and run the truck right? Anyone see any issues? Should i add a fuse or diode or something like that? I would like to have the 12v to the ignition module and fuel pump going through toggle switches in the cab instead of the ignition switch. Why? Just because. And the starter be activated by a push button.

For the alternator, ive seen some people put terminal 2(sense wire) directly to the main hot stud. But it depends where you want it to sense from? Could there be a better place to put it? Maybe the battery terminal? Or possibly the positive side of the ignition coil? Also, I wont be using the stock charge light, if I were to use an ammeter guage I would wire it as I have it in the diagram?

 

What's wrong with the existing harness? My 82 had a rat infestation under the hood. It sat for 2 years out in the country. I have pieced my harness back together. That seems simpler or it was for me. The FSM wiring diagram was very helpful.

 

Yah...if you're doing this just to understand the system that's a lot of work man! When I 'fixed up' the wiring in my 83, I photocopied the FSM wiring diagram several times, then used coloured markers and traced out each circuit I was working on from the battery to the loads for each fuse link/fuse. At a glance I could see what did what. Any changes where penciled in and then highlighted on the copies...one copy for each change.

I don't know much about the GM 3 wire alternator but as much as I know isn't terminal #1 for the charge indicator light? Hooking up an ammeter there may not work with consequences ranging from just not working to deep frying electrical parts/system. I just briefly looked up GM 3 wire alternator wiring schematic and there seems to be a lot of info on how to do it.

Did you try the dealership for a FSM wiring diagram?

 

Yes you need fuses, that's a fireball just waiting to happen! Remember it's not just your life you put at risk but other drivers and first responder's aswell, please.

Starting at the battery you need FL rated for the maximum current of the systems plus a little room to grow ~=80 amp (FL#1). A distribution plate goes at the end of this where you will tie in other circuits (D#1). From this (d#1) you then need an FL rated for the charging system (FL#2)(60amp?), at the end of this is where your alternator sense wire goes (sense wire goes as close as practical to the battery so the alternator output compensates for the voltage drop of the charge wire).

Now you can branch off the D1 your various draws, via fuses or fusible-link, like your ignition, starter, and fuel pump.

Both your starter button and fuel pump should have relay circuits, not using relays will kill your switches due to high current arcing.

PS odds are Autozone repair guide website has the wiring diagrams for vehicles going way way back..

 

I'm aware i need fuses, don't worry ha ha. I'm not a rocket scientist but I'm not dumb either, I know this is lots of work but i wouldn't be attempting it if I wasn't confident i could do it. Electrical is my weakest subject but I'm here to learn.

To add more detail to my question, I wasn't asking fuse or no fuse, but when, where, and how big of fuse. Im guessing that I should only need 15A and 20A fuses, that's what it had before. But as an example, if the wire harness uses a 15A fuse for the wiper/radio circuit and i split these 2 circuits up into two separate circuits do they both get a 15A fuse?

Stupid question-- is a fuse protecting the the wiper motor from the battery/alternator? Or protecting the battery/alternator from the wiper motor?

For relays, I understand what a relay is and how a simple one works. Correct me if im wrong but they are basically a switch in a high energy circuit and the switch is controlled by a low energy circuit. But where do you tap in to high or low amps?(another stupid question)

if I'm going through all this work anyway, why not mount switches in the cab that can take the heat? I found a momentary pushbutton switch that is rated for 30A, the solenoid is a relay, a 30A button should be able to turn the engine over with a very simple circuit to the solenoid? The headlight relay says 20A on it, why can't a 30A toggle take its place. Why not use 20-30A toggle switches instead of the oem headlight switch, hazard light switch, blower fan switch, wiper switch. Seems simpler than using a relay. I don't need such a HI-LUXury vehicle, I don't need 2 wiper speeds, 2 blower speeds, or a dash light dimmer, just on and off. I'm taking the radio out completely, removing all warning/ indicator lights on the dash, installing oil, fuel, temp, voltage, gauges. I just need help on the bare bones wiring. I just want the truck to start, run, headlight/taillight/blinkers, wipers/heater and I'll be happy.

can anyone tell me what this is, I'm 90% sure it's a resistor but for what? why is it needed? And for what circuit? its mounted on the passenger side fender near the headlight relay. The female end has 2 thicker black wires coming from it.

 

THIS! ^^^

I’m going the same route (when the weather warms up!) with the same thought process. Start? Push the button. Need wipers? Flip them on. Heater fan? Flip it on. Radio? ...for what?
Going to start with a custom dash (think off road truck). Dash will fold down revealing fuse block, relays, etc. A few gauges, but prolly no tach or speedo (just unnecessary IMO).

Post your progress!

 

Wasn't a dig or anything, you specifically asked (I'm gonna paraphrase) "do I need a fuse, what about a diode?"

So I gave a few examples of what kind of circuit protection you wanted and where, specifically fusible link wires. FL wire is used for several reasons a big reason is they are what is considered "slow-blow" which means they don't just go poof due to things like in-rush current. Where your typical 20A blade fuse sees 25A it "instantly" says nope and pops, a fusible link will take a substantially longer time before it cuts the circuit.

We use old barrel style fuses for example and you can get these in a slow-blow fuse, these are a midrange between FL wire and insta-blow.

..

Fuses, regardless of the type, are there to protect the wiring and you want them as close to the source as practical or where you go from a wire capable of carrying say 600A (battery terminal) to a wire capable of carrying 60A (your alternator charge wire).

You can see this in practical use in the OEM wiring of our trucks, and also in your home. In your home wiring there is a (gonna make some ˟˟˟˟ up here, be kind) 1" wire coming off the utility pole it runs to your meter and then into a 200A circuit breaker then from that circuit breaker there is a 1/2" cable buried in your yard which leads to the box on the side of your house and branches out in your panel for a 100A CB for your electric dryer which has a 1/4" wire and your microwave has a 25A CB protecting a 12g wire.

This makes sense, ya?

...

Ok so what size fuse to use and where depends on the current handling of the wire down stream. You can look up these on handy charts, conveniently these are also printed (typically) on the wire sheath.

So the next question is what size wire do I need to use where. Also conveniently these are printed on things like your car stereo and wiper motor in an off hand sort of way. Let's take uhm headlamps as an example, on the headlight bulb's package you will see 53watts (sorry making ˟˟˟˟ up again because I forgot if that's one bulb or two) the formula is watts/volts=amps 53/12=4.41(and suddenly I know that's 53w per bulb, why because we use 10A fuse normally on head lamps) this tells me I need a wire capable of carrying ~9A at 12volts which is somewhere in the range of 10-12g if my memory serves me.

Still following right?

...
You're protecting the wire not the device so no, but yes depending on the wire guage. My aftermarket stereo, and most auto stereos, uses a 10amp fuse. So it consumes less than 120watts.

A better question is what size wire do I need to use for my stereo sub harness so that I can safely pull 10amps at 12volts. The answer to this depends on how far away it is from its power source is it twelve inch's or twelve feet.

If you don't like math and engineering your probably not having a lot of fun right now. But onwards and upwards!

...
Short version of all the babbling above. Fuses protect wires.

..
"Why a relay instead of a switch?"
Life span, among other things!
Switch's are typically rated for tens of thousands of cycles (~50k, for a good one), where relays are rated for hundreds of thousands (100k-1million).

So you take your 50k cycle rated switch that can switch 12v and carry 30amps and limit it's current to oh say 1A and now it lasts oh let's say 30 times longer (yep pulling numbers out of my butt, but it's close enough). You'll find this kind of information in the switch/relay's "data sheet".

Still following?

.. Oh I skipped a question, but it fits good here ..

Ok so the flow goes like this..

Battery->100a fuse->distribution block.
Distribution block->10amp fuse->9 one amp relay control switch's.
Distribution block-> Nine 10A fuses-> Nine relays switching 9 amp loads.

.. Gonna stop here my battery is low and well Dinner!

 

Oh and there is fun stuff, like "in rush current" when you hit the power button on the radio, and your DC motor driving the wipers before it starts moving pulls infinity current.

 

Thought I sent you a pic of this and an explanation in another thread. That is the Fuel Pump resistor for the original pump circuit. In "RUN" mode, it drops the battery voltage to the fuel pump to about 9.8 volts, to reduce pump noise & extend the life of the pump.Since you now have the Mr. Gasket pump wired direct and aren't using the original pump, this part now has no purpose.

 

Ive sorted out the harnesses. Its alot of work but boy do I understand it now. The stock harness is pretty simple but still seems difficult to diagnose, seems much easier to diagnose separated out. I ordered a haynes manual for the wire diagram but its back ordered 2 months.... I took the harness apart and separated all the circuits. Ive drawn a diagram of all the lights. I took the headlight and hazard switches apart to see how they worked and map them out, they are simple and pretty neat the way they work, so I'll keep them. Ive got everything wire loomed and taped up, looks great.

I'm going to wire the ignition system and starter solenoid into the key switch. There are 4 wires coming from the switch, correct my if I'm wrong, one of those wires goes to unfused power and is hot, and when the key is turned(depending on position) distributes the power to the other 3 wires? 12v goes to the switch, and when in crank position will go to starter and coil, then in run position only coil. So I'll probably only use 3 wires out of the 4? I don't need to wire anything up in the Accesory position right? Just gotta make sure I turn everything off? I got a fuse box that is a distribution plate with a stud. Should I fuse the switch and then the coil and starter would naturally be on the same fuse? or connect the switch to the stud on fuse box and use inline fuses for the coil and starter?

Ok so from my battery ive got a fusable link to my headlight harness, Check, but why not an inline fuse? The FL is not rated for a specific amps, it just says 14ga. I'll run a 8ga cable from batt+ to the fuse box stud. I'll run another 8ga cable from ALT to the fuse box stud(or to batt+?) Again why not a 80A fuse here? If there's a spike the FL won't blow quickly, I see, but isn't that the point? That would give time for your wireing to get burned up? The guy at the parts store was surprised I was asking for it.

I'm confused how to wire my starter solenoid. I pulled a red wire and a green/yellow wire off the solenoid. All diagrams I can find have only 1 wire going to the solenoid(im NOT talking about the big red cable to starter motor). Is one of these 2 wires not necessary?

Also is the speedometer in this truck completely mechanical because cable coming from transmission? Theres wires for the bulb there but theres also 2 black wires going into the spedo, are they necessary?

for my lights harness I've got 5 wires coming out that need to go to the fuse box. 1 for the hazards, 1 for the blinkers, 1 for the brake lights, 1 for the running lights, and 1 for the horn. From what I can see, the stock fuse box has 1 fuse for running lights+meter, 1 fuse for horn+brake lights, 1 fuse for blinkers+gen. Why split it up this way? Would it be safe to run blinkers, hazards, brake, running lights and horn into 1 fuse? 20A? 30A? And what us gen? If its generator, as in alternator, whybis it on a 15 amp fuse.

 

I did throw a response out to you on your recent post on the public thread, but I will go through this message as well.

Nice work on the harnesses. Nothing beats "doing" in order to learn something. Here are 2 links to online PDF files for the wiring:
http://www.globalsoftware-inc.com/co..._LC_Pickup.pdf
http://www.offroadforum.cz/toyota/aa...8/85786148.pdf

The second one (Chilton) seems to show the ignition switch better, and also notes the wire colors going to it. You can trace where the wires from the ignition switch go on that. Since you are basically doing a "custom wiring job" you can wire it however you want to, as long at it does the job you want it too. In the original, it appears the switch is wired to the fuse panel (distribution plate) in 2 ways. If you study the diagrams for a while I'm reasonably sure you'll figure out what's needed.

About fusible links. First & best explaination is the Wiki article on it here: https://en.wikipedia.org/wiki/Fusible_link

Basically, a fusible link takes advantage of a certain gauge wires ability to handle a certain amount of current, due to it's inherent resistance, like we have been discussing about differences in wire resistance i.e. you 9 foot runs to the ignition module. As you can see,the "standard" way to do this is use a wire that is 4 gauges smaller than the wire the fusible link is protecting. Smaller gauge wire will not carry as much current as a larger gauge, and the conductors will melt & "break" after a given amount of time, thus breaking the circuit & protecting everything that is "downstream" of it. The one crucial difference in fusible link wire over "regular" wire is the insulation. Fusible link insulation is designed & made to stay intact when the inside wire(s) heat up & break. This is to prevent a fire from happening. Fusible Link wire is NOT rated in amps, but by gauge size.

Why fusible link over a fuse? Two reasons. One - The Fusible Link wire acts like a "slow blow" fuse, and does not "pop" quickly like regular fuses. Most DC electrical systems, especially automotive, experience frequent surges, so you don't want the "fuse" popping off with every surge; that would get damn inconvenient & expensive for fuse replacement. Reason Two - Fusible Links are usually meant to protect a wider circuit system, rather than a single circuit, like in a typical car fuse box. It protects the whole wiring harness. That's why it's the first thing the battery "sees" in the main power feed line coming of it.

You can run your new harnesses without a fusible link if you want but I don't consider that to be very safe. Personally I like having one there for safety & to protect the harness system. Using 8 gauge is a bit overkill but I'd at least put in a 12 or 14 gauge Fusible link in it, somewhere between the battery & fuse block. You keep mentioning an 80 Amp fuse. If you wanted to use one go right ahead, but I'd recommend you get a "slow blow" type, or you might find yourself blowing that fuse quite a bit & having to constantly replace it. I replaced my stock Fusible link on my '78 with a 14 gauge unit from Dorman. There are sold in most parts stores for $5-$6. The parts guys may have been surprised you were asking about one because it's not common for these to blow. My old one was still functioning, but I just wanted to get a new one in there when I did my wiring job.

Starter - If you look at the second wiring diagram, you'll see the wiring from ignition switch to starter. I'm not exactly sure about this myself but would think there is only one wire going to the solenoid from the ignition switch, as a triggering circuit. In most older vehicles this is pret6ty common & can't think why it would be any different. The Green/Yellow wire may be a separate circuit for something else. The second diagram shows a Green/Yellow wire going to the directionals (turn signal lights) from the Hazard Switch.

Yes,your speedo is mechanical, cable driven from the transmission. I haven't had my speedo cluster out for a while (I replaced all the bulbs in it with new & cleaned it up) but if I recall correctly there is a multi-terminal plug that goes to it from the harness. I think this is shown onthe second page of the first diagram, marked "Printed Circuit Control:. I have no idea about the black wires you mention. I guess you might have to trace them out.

The circuits in a car or truck are divided for several reasons. One is that when something malfunctions, it can makes it easier to track down & fix. Also if you have so many items on one fuse & the fuse goes, it could completely disable the vehicle. You could get stranded somewhere just because of a simple short in your tail-lights. With the circuits divided up the way they are stock, you could have a short in the tail-lights but still drive the vehicle. Another consideration is current handling. It is much safer to have several lower amp circuits rather than one big one. Again, higher current draws can cause a lot of heat in a system. That's why we use larger gauge wires for higher current items, like the thick cable going to the starter. 4 gauge cable is good enough to handle the job & be safe, because the starter is only drawing current for a short period of time, enough to start the engine. If the starter was runs for a longer period of time or continously, you'd need something like a 0 or 00 gauge cable, 4 or 5 gauges larger, so it wouldn't melt under the "pressure" of the high amperage. The larger the wire.cable, the more it can handle. hich leads me to reason three - separating out the circuit you can use lighter/smaller gauge wire. This reduces bulk, weight and cost. Also smaller gauge wire is easier to run in the sometime tight spaces found in vehicles, as it's more flexible than larger wire.

I do not know why that one fuse is also marked "GEN". That circuit on that fuse appears to be for the hazard & turn signals only, if you trace it out on the diagram.

Hope the above answered your questions.

 

When doing a GM alternator swap... The pully on the GM alt is smaller than the one on the toyota. Should i swap them. Do I want the GM alt to spin faster? Is there a too fast?

 

Im wireing up my ignition switch, ive measured the resistance between the main power wire black/red, and the wire for the ignitor, black/yellow. To see what's connected when, and it is connected in the on and start positions like it should. But it is reading between 20 and 50 ohms!!!! Not milliohms, ohms. Ive measured my soldered wires from the plug down and they are fine, I can measure that resistance from the plug upstream. I'm sure that's not normal but i may be crazy.

 

I'd say as long as the smaller pulley on the GM Alt isn't that much smaller than the Toyota you shouldn't have to worry about it. How much difference is there exactly? Have you measured them? I checked some previous posts on that swap and I see very few mentions of there being any problems with it, especially if the GM Alt is the 10si or 12si model. SI stands for "Systems Integrated", meaning the voltage regulator is internal to the Alt.

The alternator speed is all about pulley ratios & engine speed. The 20R pretty much redlines at 5000 RPM and you aren't likely to even get close to that speed in normal driving. On my '78 with manual 5 speed the upper limit of the shift point is about 2000-2500 RPM. So even with a pulley ratio of 2 to 1, crank to alternator, alt speed should be 5000 RPM max. Max output for most alts is 6000 RPM, so that's within range.

Ignition Switch - Are you sure you're just measuring the end points of the wire? Are you measuring resistance with the ignitor hooked up to the circuit, or disconnected? Generally when measuring an item for resistance, you need to isolate the item being measured (disconnected from circuit). Measuring it "in circuit" and connected, you may be reading the wire plus other items connected to it. Just temporarily disconnect the ignitor from the wire, try another measurement & see what you get.

 

I'm measuring the resistance of the switch from the green plug on the steering column it's not connected to anything. The 4 wires come out of the switch, travel maybe 10 inches down the steering column to the green plug. Disconnected the plug and measured up towards the switch.

 

So you're measuring the resistance of the ignition switch itself, got it. Basically speaking and depending on position, the switch should either read near zero Ohms (RUN or START positions) or infinite resistance (OFF). If you are getting a 50 Ohm reading in either the RUN or START positions I'd say the contacts in the switch are bad or going bad & the switch should be replaced. Again, you're looking at a 43 year old part that has carried current for a long time, so it's reasonable to assume the contacts in it could be worn or damaged. Either could cause excess resistance.

Here's the part: https://www.rockauto.com/en/catalog/...er+switch,4700

Notes: You do NOT have to remove the key lock cylinder to replace the switch, you just have to remove the lower half of the plastic shrouding on the steering column (6 screws). There is one screw that holds the switch in place. It's a bit of a fiddly job but you can get it done; I did. Here is the video I did on it:

 

I ended up just using a toggle for the ignitor. All finished now, the truck fired right up, everything works great. It was a ton of work, but worth it. The mount I made for my GM alt is a little bit wonkey, the pullys aren't lined up 100%, it's real close but not perfect. It seems to run alot smoother now for some reason, doesn't vibrate as much or at all, don't know why.

so when you changed out the distributor wires, did you un-solder them from the pickup coil? I may end up doing that, it's probably the weakest link now but it's fine for a while.

 

Glad to hear that the hard work paid off. It's always worth it to get these old 20R's & 22R's going again, they are great running engines when everything is working right. It's probably running a lot smoother now because you fixed all the electrical & ground problems, and the ignition system is now seeing full voltage. It always amazes me how that works.

Pickup Coil Wires - I didn't go so far as to un-solder them from the coil, but that would be the best, most complete solution. Wish I had thought of that at the time I did mine. I just cut the old wires off, leaving about an inch and a half on the module side of the green plug. Spliced in (soldered) new wire, insulated, wrapped with aluminum foil for shielding then shrink wrapped & went from there. Added some ring terminals on the other end & connected to the module. Seems to work just fine.