We have a *cough* GMC *cough* bucket truck at work. Circa 1973. It is a big truck (comparable to a F-700). It has a 366 CI V8 gas engine.

It seems to go through starters about every 8 months or so (AC DELCO). That is besides the point.

The question I have is the wires that go onto the starter/solenoid. It is one unit. There is a battery cable and a couple other wires (I am assuming one for the alternator) that hook directly to the big terminal on the solenoid.

Then there are 2 smaller terminals on the solenoid. 2 wires go on one and one wire goes on the other. Here is where the problem comes in.

On Friday my Dad and brother had the truck out doing some tree work. He went to start the truck, after using it for a few hours, and it wouldn't start. He looks on the solenoid (which is part of the starter) and 2 of the wires had come off. So, my brother hooks one of them back up and my Dad starts the truck up. But, they look and see some smoke and the other small wire is touching the frame and is getting burnt up. It goes from the solenoid up to a panel type box on the driver's side of the truck under the hood.

So, they pull the wire out and leave the truck for me to come and fix. I go and hook ONE of the THREE wires onto the solenoid and start the truck up and it runs fine. No problems at all.

What are the other 2 wires for that I didn't hook up? I am assuming the one I hooked up is from the ignition when I turn the key telling the solenoid to engage the starter. But, I am baffled about what the other 2 wires do.

If I don't need them I might as well not hook them up but I am sure they must do SOMETHING.

Help.

-Matt

 

The extra wires may be specific to this truck. The starter only needs the one wire from the ignition to start the truck. Do the extra wires have voltage on them?

Earlier distributors had a dropping resistor for the ignition points while the engine was running. The starter solenoid would use the extra terminal to bypass this resistor during engine start to allow more current for engine start. Your truck should have the HEI distributor (large distributor cap) and doesn't use this bypass circuit. jd

 

Well, I know the one wire has voltage when the truck was running because it touched the frame and burnt up. That wire went from the solenoid up to a type of box on the driver's side under the hood. A whole bunch of wires went into it at different terminals.

I guess I should just check for voltage and see what the wires are doing.

-Matt

 

matt, the gm internal voltage regulater style alternator has a 3 wire hookup. in the plug, you have 2 wires. one is switched 12 volt to excite the field to induce charging, and the other is for an idiot light. then you have the larger single wire that is a constant hot 12 volts

on some of the larger vehicles, the 12 volt constant is taken off of the starter. it is very possable your truck draws its power for the battery charging directly from the starter.

and as jimdandy said, you may also have a ballast resister in line for running, and a hot wire off the starter for 12 volts to the coil for startup.

 

That panel box isn't regular setup for GM, can't say what it is for without more info. The way GM wires all their vehicles generally has been battery to starter post, then distributes main power from there. Only one wire is needed to make the solenoid work, connect the starter motor to the battery, and pull the bendix out to engage the flywheel. A 73 proper would not have HEI, that didn't come out until 75 on GM vehicles. The resistor wire is between the ignition switch and the coil, had nothing to do with the star5ter. Same for the alternator energizing wire. Sometimes they had a safety switch wired to the other terminal, the outside little one, that would prevent you from cranking the starter if the trans wasn't in park or neutral, or clutch switch wasn't depressed. Otherwise, they have added something for the bucket part of the truck for whatever the reason. It is possible it is a resistor wire bypass as well, which makes the mst sense, or perhaps something to keep from cranking if the hydraulics of the truck are engaged to protect the truck or operators from damage.

 

This wire is for starting the truck. Seems to be coming from the ignition switch (key).

There was another wire that burnt up that went up to that box (from the terminal on the solenoid that the above wire was hooked on) under the hood on the driver's side. I looked on the rubber flap and that wire is supposed to do the same thing the other wire that is hooked up (activate the solenoid). Why would there be two wires doing the same thing?

Anyways, the truck seemed to not really start (it would just keep cranking over) until I let go of the key then it would start. Yeah, I know...weird!

So, I checked the last wire and it seems that it has voltage when the key is in the run or start position. So, I hooked it up and when I went to start the truck it would fire up before I let go of the key. It's fine I guess.

What does that last wire do then? Seems weird to me. I would guess the first two wires that are on the solenoid together are just duplicate wires to engage the solenoid. The other one has me baffled.

-Matt

 

the last wire supply's straight 12 volts to the coil for starting. once the ignition switch is turned to the run position, the coil gets 6-8 volts from the resister wire.