Truck stays running after ignition switch turned off

[Buckethead03]

Ok, so i just installed my donor cab on the 71 and got the front clip put back on. Got all the electrical stuff hooked up and now I've got a strange problem that i am having a hard time resolving. I have checked and double checked all of the wiring i can easily get to and it all seems to be hooked up correctly. The problem is when i go to cut my truck off with the ignition switch, the truck continues to run. It is not dieseling. The only way to get it to shut off is by pulling the positive terminal off of the battery. Even then, the truck continues to run for about 30 seconds and then shuts off. I have tried another known working ignition switch, known working solenoid, and even another voltage regulator. I have checked voltage on the coil wire. I have nothing with the switch off and 12 volts with the switch on. All functions of the switch work like they should. I only get turn signals and radio with the switch in the acc position. I am totally bumfuzzled.

My original truck was a 71 302 truck with no ac, and manual everything(steering, tranny, brakes). The donor cab came from a 71 390 truck with ac and power everything(brakes, steering, and auto tranny).

Do any of you guys have any suggestions or ever had this problem? Any help would be greatly appreciated.

[Hawkrod]

Look and see if you have the two small wires on the solenoid switched. The red wire goes to the S terminal and the brown wire goes to the I terminal. Swap them and it will run on. Hawkrod

[Buckethead03]

Look and see if you have the two small wires on the solenoid switched. The red wire goes to the S terminal and the brown wire goes to the I terminal. Swap them and it will run on. Hawkrod

I checked the two wires stated and they are hooked up correctly. I tried swapping them earlier but after doing this, the truck wouldn't even turn over.

[Hawkrod]

Look and see if you have the two small wires on the solenoid switched. The red wire goes to the S terminal and the brown wire goes to the I terminal. Swap them and it will run on. Hawkrod

I checked the two wires stated and they are hooked up correctly. I tried swapping them earlier but after doing this, the truck wouldn't even turn over.

THen you definitely have a problem because if teh wires are swapped it should start cranking when the key is turned on if the wires are swapped because the ignition bypass sends power to the solenoid. Time to get a meter and a wiring diagram and see if you can find the problem. Sorry it wasn't an easy fix. Hawkrod

[Buckethead03]

I talked to a mechanic here where I work who has worked on these old trucks for 50 years or more. He is saying i need the engine side wiringing harness from the 390 truck. The original truck has the idiot light setup while the 390 donor had all gauges. He is telling me the problem is with the ammeter wiring. He says the harness is the same but there are 2 wires that are switched somewhere on the engine side. I am currently using the engine harness from my original truck. Does this sound familiar to anyone? Thanks

[Hawkrod]

I talked to a mechanic here where I work who has worked on these old trucks for 50 years or more. He is saying i need the engine side wiringing harness from the 390 truck. The original truck has the idiot light setup while the 390 donor had all gauges. He is telling me the problem is with the ammeter wiring. He says the harness is the same but there are 2 wires that are switched somewhere on the engine side. I am currently using the engine harness from my original truck. Does this sound familiar to anyone? Thanks

I missed completely that you mixed wiring harness' and he is right "kind of". The guage versus idiot light is not as simple as just the one harness, the under dash and under hood wiring has to match, you can't swap them around. You need to either have the correct harness set for the cluster you have or have a set that is properly modified but everything from the alternator to the underdash harness needs to be from the same type of system. If you have idiot light wiring and want to use a guage cluster there are guys that have converted and you can search here on the forum for how to do it. Personally I think it is more trouble than it is worth and would simply get a compelete harness of teh correct type. The tail light harness is the same for either as are any add on accessory harness' like camper special wiring and cargo lights etc... Hawkrod

[Buckethead03]

Thanks for the reply. Just to be clear on what I have. The cab and front clip that are on the truck now are both from the donor. The only thing left from the original truck is the engine harness. It was a 302 truck. I have everything hooked up and have traced out the majority of wires under the hood with a schematic and a multimeter. With the exception of 1 wire, Everything seems to be spot on.

[SmoothJ69]

all the ammeter does is create a loop, one side connects down by the alt, the other side connects up by the starter solenoid and it shows you the difference between the 2. The dummy light is just a wire, with a lightbulb that goes to ground. I don't see how either one of those being connected or not connected would cause your issue. If your motor (coil) is getting power with the ignition off, something is not wired right, you are probably drawing power with the key off so the batt will be dead if you let it sit, and it ain't just a simple dummy light.

I think Hawkrod is on the right track, you need to look at the alt\solenoid\regulator and its associated wiring. You could always do a 3g upgrade and replace all that wiring.

[Buckethead03]

I will do some more digging tonight and see what i can come up with. I couldn't care less if the ammeter is hooked up or not, i just want to be able to use the switch to cut my truck off. I will report back with my findings.

[Buckethead03]

I think i have the running on problem resolved. It ended up being the voltage regulator that was bad. All is well again. I am going to forget about the ammeter and install a voltmeter instead. I have a nice sunpro laying around that i'm not using. Thanks for all the info and suggestions.