I have an 86 SS with a few modifications (carb, intake, headers) I have been experiencing an issue with electrical issues for a long time. Mostly issues with the aftermarket radio cutting off. I started having issues with very slow signals (sometimes a full minute before they would blink). Also noticed the headlights are fairly dim. Most of these issues seem to happen after about 5 minutes of driving. Up to that point, signals work as expected. I have completely removed the radio to see if that was causing the problem, but it didn't make any difference. I also replaced the alternator and battery recently, but didn't help. Any trouble shooting suggestions would be greatly appreciated.

 

Do you have a multimeter? First thing I'd check is system voltage while you drive. You can monitor to see what the vehicle voltage does around that 5 minute mark.

 

I don't have a multimeter. If I get one, how would I monitor while driving? Thanks

 

If you want to get into electrical diagnostic work like this, it's really the one and only physical tool you need to get started. Doesnt have to be fancy for basic 12v stuff like this - plenty of inexpensive models out there.

To check while driving, I'd probably start at the radio plug since you mentioned you already pulled the radio once. You can monitor both constant 12v and the switched 12v ignition (separately of course). You can just pull the radio and probe the connector directly. Unless there's a ground issue on a certain component, this should give you the baseline for the whole electrical system.

 

Thanks for all the details. I'll get a multimeter and try this. I appreciate the help.

Brian

 

I was finally able to test with the multimeter through the radio connections. Had constant output until I would accelerate through a right turn. As I would go through the turn, the fasten seat belt light would turn on and the voltage would drop considerably. I disconnected the wires that plug into the seat belt connector, thinking there might be a short there. Didn't make any difference. The light would still come on. Any suggestions about next steps would be greatly appreciated. Thanks

 

Check your frame, body and chassis grounds. The negative wire on the battery terminal should have a very large (about the size of a magic marker in diameter) black wire that goes to the engine block. There should also be a smaller black wire that is on the same negative terminal post of the battery that goes to the body ground, fastened to the body somewhere near the battery with a 10 mm head bolt and a star washer. When you get strange results on the electrical system only turning right or left, or when the engine bay warms up, then something is moving. Grounds on old cars like this is definitely a suspect.

I just finished work on an old '69 C10 where the owner had electrical problems just like this. The problem was, there was no good bond from the negative of the battery to the BODY. There WAS a good ground to the engine block. However, the block of the engine and the car body is electrically treated separately since the body rides on the suspension system. If the body of the car, which is common negative for ALL electrical stuff EXCEPT the starter, is not well-connected to the negative of the battery, you are relying solely on the engine/transmission mounts and shocks for your grounds to make connection which is not good.

Take a wire brush or Dremel tool with a brush or light sanding tip and clean the paint off a dime-size spot on the body somewhere under the hood. Use #10 wire minimum and a yellow crimp lug with a 1/4 inch eyelet hole and attach the wire to body ground on one end and to the battery negative on the other. Use no-oxide compound under the lugs to ensure a good, long-term connection. See if this helps. I have the body of my vehicles bonded directly to the I-beam frame of the car in several places, and the I-beam bonded to the block as well.

Best of luck.
Derek.

 

Thanks for all the suggestions, Derek. Turns out the small ground on my negative cable had been cut at some point and was merely twisted back together and covered in tape. I replaced the negative cable and haven't seen any problems since then. I wouldn't have thought to change that if you hadn't mentioned it. Your help is very much appreciated.

Thanks again,

Brian

 

Excellent, glad it helped!

All the best,
Derek..