Well, I just picked up my first Toyota pickup and trying to figure out some problems I'm having with it. Its a 1978 2wd 4sp manual 20r and with only 85k confirmed miles.

I'm having some weird problems with the tail lights. By themselves tail lights work and are as bright as expected to be.

Turn signals work until you think touch the brakes. Then they don't blink and the opposite turn signal lights up and stays on.

Tail lights work until you hit the brakes or turn signals.

Hazards cause the brake lights to flash not the turn signals. They also only work until you turn on tail lights or brakes.

Basically only one function works at a time. So here is what I've done so far.

Pulled all bulbs checked and replaced. Cleaned all studs and nuts on tail light ground connections. Checked wiring under bed on both sides and found what I assume is a ground connection above the tailpipe that crosses between the two sides a black and white with black stripe. So I cleaned up a section on the frame and replaced the connection. Also ran a secondary ground wire from battery negative to body. Checked all the fuses all OK. Went looking for the blinker relay. Pulled the after market stereo the PO put in and found it dangling. Remounted it back on the firewall where it was originally. I noticed that actually seemed to function for a little bit with the brakes pressed like it should. Then nothing. It quit working and now nothing. Fuses are still OK. Just the clicker does nothing with turn signals or flashers. Ohms out at 2 ohms

Sorry so long just trying to be acurrate as possible.

So as of now I have either tail or brake but not both and no turn or hazard. Reverse lights do work now.

 

Now I notice my warning dummy lights all 3 are lit when brakes are pressed and charge light stays lit while running.

 

Make sure that you have the correct bulbs in the tail lights. My friend had a jeep and had the wrong bulbs in it and his lights did all kind of crazy stuff.

 

Makes sense , I just replaced what was in there with new ones of what I took out. I guess I shouldn't assume they were the right ones to begin with. 1156 and 1157 if I recall but will pull to verify. Thanks

 

Very interesting...

Possible...

Hmm.. sounds like electrical charging system interference VIA the alternator.

Verifying correct bulbs is defiantly a good place to start.

 

OK here we are, after checking wiring and connectors I find this





The green connector behind the fuse panel is melted on what appeared to be heater fuse mainly on the power supply side which explained why fuses weren't blown. So I wired in a different fuse box of a different type but should accomplish the same thing. Lights are still messed up. Just as screwy as before but now I notice that I have a buzzer and dash indicator lights when key is turned to the run position. And the charge light is now off while running. Lights give problems with key on or off engine running or not. I have also been looking for a repair manual for the wiring diagram and it seems that nobody carries it. Oh well.

Also BTW I have what appears to be an aftermarket ac installed on this rig.

 

I'm thinking now that I have a short between signal wires to rear as grounding all checks out. Hazards flashing I get the full voltage on one wire brake while getting partial voltage signal on turn wire. Unplugging one side or the other does nothing. Lights work properly when bypassing wiring at the connection behind rear bumper and sending voltage direct to lights.

Do all tail / turn have any other junction point in common? Such as hazard switch?

 

OK PROBLEMS SOLVED!!!

1. Brake and turn wires coming from the turn signal dimmer / multifunction switch were nicked as if there was a splice connection at one time - repaired

2. Crispy wires behind the fuse box - replaced box with newer type

3. Side rear marker lights had rotted apart and was shorting out - disconnected both sides

4. Ground wires for the bed were rotted off - this is the one above the tail pipe that I had cleaned replaced and connected tothe frame. When I should have mounted it to the truck box. Found out when ohmed light ground to box and was good but checked box to frame and had 2,500 ohms! - so I also added two new ground wires from each tail light directly to the battery negative terminal.

 

I finally found a Chilton's repair manual. Has anyone here noticed that the chassis wiring diagram is wrong with some of the trucks as far as wire colors???

 

Great repair!

 

My 78 is doing the same thing. But when my headlights are on nothing works but the running brake lights.

 

On my truck I found 2 grounds one at each lower corner of the radiator. Then added one to each rear light mount.

 

Chiltons? You mean the one that covers trucks from 1902-2013?

Yeah, the wiring diagram won't be right. Things changed every year, sometimes multiple times a year. My 1983 Toyota Factory Service Manual (printed by Toyota for the 1983 model pickup truck) had a few wrong wire colors here and there.

No way I would trust a wiring diagram from Chilton or Haynes other than to give me a basic idea of where wires run.