I I'm trying to understand how to add a sound system to an 85 Toyota pickup. There are plenty of things that this truck didn't come with like a tachometer and a cigarette lighter accessory and I'm wondering if that is reflected in the fuse system if that changes anything. I understand the very basic electrical circuit. I don't understand how to test if the electrical system can handle the addition of certain accessories such as a modem stereo receiver and an amplifier/subwoofer. I believe it's measuring the amp draw, but don't know how to do so accurately with this fluke 87 or Innova 3200. I believe the fluke can measure that, but not sure about the Innova 3200. With the stereo receiver if I knew the settings exactly I believe it's just measuring the amperage at the point of installation for the stereo receiver. But how to test whether or not my truck can handle an amplifier subwoofer combo at all is something I don't quite get.
My common sense says it should be able to but I do not want to actually complete the circuit unless I'm sure I'm not going to blow something out.

 

An 85 could, most likely handle the addition, or replacement, of it's OEM stereo with an aftermarket, modern day stereo system with no alterations to the power provision circuit.

An amplifier/subwoofer setup would be an entirely different animal. They draw a good amount of current, and the regular radio circuit probably couldn't handle their current draw. The paperwork that comes with the amplifier and subwoofers, not to mention the new stereo system, should have the recommended current capability of the power supply for them. Most likely you'll need to run an entirely separate circuit from the battery for the amp/subwoofer. Including fuses, and wiring sizes, although often they come with fuses already built into their supply wiring. In that case, you just need to run a similar sized wire to the one with the fuse already in it to the location you plan to install the parts. A slightly larger wire is acceptable, but never, ever go smaller.

Honestly, the easiest way to tell what the current carrying capability of a circuit already in the truck is to look at the circuit's fuse, then subtract 15 to 20% for normal operation. That will give you an idea of the normal, constant, current carrying capability of the circuit. So if the radio circuit has a 15 amp fuse, check the stereo's paperwork and see if it draws anything over about 12 amps. If so, you'll need to run an entirely new, separate, circuit for it.

Does all my babbling help at all?
Pat☺

 

Considering that my battery says that it has a capacity of 600 amps won't that blow out my 10 amp multimeter fuse? That's a big part that's hanging me up is that I don't know how to test it with this multimeter when it says that the most it can handle is 400 or two even 200 milliamps on one setting and then 10 amps on the other. That's a far cry from 600 even though I know that it doesn't actually draw that much when it cranks but still anything over 10 technically should blow out the fuse shouldn't it? I always have the dumbest questions that nobody answers on YouTube.

 

Only dumb question...

You're confusing CAPABILITY with USAGE.
For example, yes, your battery is CAPABLE of producing 500 amps. If you were to put one lead of your meter on the battery positive, and one on the negative, with the battery disconnected from everything, first, your meter would immediately burst into flame, melt all over the place, and instantly become useless, even as a paperweight. Connecting the meter directly to the battery, yes, it would get the full 600 amps through it that the battery is capable of producing.

Now, IF you were to, let us say, install a CB radio that uses, according to the manufacturer, at most, 5 amps. You can connect it's power wire directly to the battery, again, as an example. IF you were to pull it's power wire off the battery, and connect your meter, on the 10 amp scale, with one lead on the battery +, and the other lead onto your radio's power wire, so that you have essentially, a straight wire to the radio with the meter as part of it. If you were to the max out the radio, say by transmitting at it's maximum capability, your meter would then indicate 5 amps.
The battery is still CAPABLE of producing 600 amps, yes? But the radio only USES, or draws, at most, 5 amps. Since the meter is in line with the radio, all that will flow through the meter is the 5 amps the radio can DRAW. See the difference?

When using a meter in volts mode, AC or DC, doesn't matter, you connect the meter in parallel to the circuit under test. If testing AMPS, you connect the meter in series with the circuit under test. Like, if you want to see how many amps the starter pulls when cranking. You would pull the positive cable off the starter, and, imagining a meter capable of reading this much, connect one lead to the cable you just disconnected, the other to the starter. All the current the starter will DRAW, when you turn the key to start, will go through the meter, and you can read it as it happens.
Probably 25-30 amps draw. Battery is still CAPABLE of producing 600 amps, but the starter won't DRAW 600 amps.

If it makes it easier, imagine the whole thing as a water system. Volts, the battery's +12 VDC is the pressure pushing the water through the system. Let us say you want to run a small sprinkler off your system. You plug it into the system, and put a meter in line with it to see how many amps (how much water) flows to the sprinkler. Pretend in your mind that it only allows 5 amps (say 4 gal/min) to flow at any given time. The meter will read the 5 amp flow of water, which is all the sprinkler will allow to flow at any given instant.

Does all that rambling make things as clear as mud?
Pat☺

 

You've been incredibly helpful. Last question. Having a new circuit with the power wire from the battery to the amplifier, won't that drain the battery? I would need to create an open circuit as I need it to be hooked up as an accessory so it is only completing the circuit when I turn the key correct? I know I phrased that horribly but I think you get what I mean

 

In theory, a battery is only discharging if an accessory is left on or mis-wired. When you say your battery has 600 amps capacity. That is rated at 600 cranking amps, for the start circuit which may max out at 80-100 amps. Normally a new stereo will rated as an amp draw. Check the fuse capacity on the radio will tell what size power wires you need, running a fuse from your fuse block to the radio. For the sub, there are numorous ways to power one. go with the manufacturers recommended setup and just follow their direction to be safe

 

If you were to run the amp's power wire directly from the battery to the amp, with a fuse somewhere along that line, whether it drains the battery or not depends on whether it has draw for a "keep alive" circuit, and/or whether you leave it on all the time. Keep alive circuits have a very slight draw, so they don't drain the battery, unless you leave the truck sitting, shut down completely, for a period of time. 5 days, a week, whatever. The truck's ECU, and other computers, often have heep alive circuits.
Generally, radios have a keep alive circuit built in. Keeps the settings stored in the radio, frequencies preferred, just a lot of different settings, from being lost when the key is turned off. It's generally a wire direct to the battery, or to an "always hot" circuit in the cab. Brake lights, head lights, etc. Something you have available with the key on or not. It's totally separate from the radio's "power" wire, which is often connected into the Accessory circuit, ie, only on when the key is in ACC or RUN. Like, for example, the Radio, or Accessory, fuse in the cab.
Most amps generally don't have a keep alive circuit. They don't need it, unless they have a digital graphic equalizer, or something similar, built in. IF it's draw isn't too great, you can frequently run the amp's power off the radio. Many are designed to power an amp, so you don't need to worry about the amp having a seperate power wire to the battery, or some other fused supply circuit. Often the radio will have a wire for connection directly to an amp. That way, you can't turn the amp on unless the radio is on. Thus, unless the key is on, yes? Read the radio's paperwork to see if it's designed to power an amp, and if so, how many amperes max the amplifier can draw. Then, check your amp's paperwork to verify how many amperes it draws, max.
IF your amplifier draws too much to run it off the radio, or the Radio/Accessory fuse, you will need to run it off a different fuse that can support the amp draw. Or directly off the battery, with the proper sized fuse in the circuit. Given the size of the fuses in the engine compartment fuse box, I'm certain you'll be able to find one you can tap off for the amplifier. Presuming the amplifier draws a huge amount of current. There are amplifiers out there that draw massive amounts of current. Read YOUR amp's paperwork for it's correct connection to a power source, and it's correct fuse rating, if there isn't one included in it's power supply wiring.

What I'm saying is, yes you COULD run the amp directly off the battery, but you probably won't need to. If you do run it directly off the battery, it won't drain the battery unless you forget to turn it off. Like the headlights. Not that *I* ever left the headlights on. <Ahem> You forget to turn the headlights off, they will drain the battery too, right? At least on the older trucks. 3rd gen and up have a circuit that will shut them off a specific period of time after the key is shut off. A super good addition to the head light circuit, IMO.

Bear in mind, if you add multiple devices to a given fuse, you need to check their paperwork to see what each device's maximum current draw might be. Add the maximum current draw for each device added to a fuse together. The grand total must be less than the fuse's rating. If not, you'll need to move one, or more, to a different fuse for it's power. This doesn't apply to keep alive circuits. They draw very small amounts of current, and, since they generally connect to an always hot circuit, they are generally not connected to the same fuses as the main device's power supply wiring is. Thus, you could easily wire the keep alive supplies all to the same fuse, without really worrying about their current draws.

Have fun!
Pat☺