Strange Electrical Phenomenon

Maintenance/Repairs
1

My '53 Chevy Truck with newer V-8 engine and 12V electrical system. It is equipped with electric radiator fan, AC system, modern radiator. All sort of tagged on as time evolved. Everything is operational, but every so often, the radio & AC cuts out with a spike in discharge. It comes back on after about minute, and then does it again. It does not seem to matter whether the radio and/or AC system is on. Any idea what is causing this?

2

“spike in discharge”? wha? Are you saying that the voltage reading jump when this happens? If so, suspect a bad voltage regulator.
Be warned though. If the entire wiring system has been fabricated ANYTHING is possible.

3

I would check to ensure all the ground connections are clean and wrench tight.

Make sure the alternator is properly grounded as well as the engine is grounded to the chassis.

Are the battery cables new or old and possibly cracked?

4

Make sure there is a heavy ground to the engine block, directly from the battery. Also a substantial ground to the frame AND a third to the sheet metal body at the firewall.

5

I don’t understand- you say the radio and AC cut out but then say it doesn’t matter if they are on or not. How can something cut out if it is already off?

6

I’m saying that if the a/c is on and the radio is off, the a/c cuts out. If the radio is on and the a/c is off, the radio cuts out.

7

Acquire an electrical schematic of those two wiring systems and use a meter and maybe find a short or perhaps a bad relay?

8

OK, I understand.

Now, what do you mean by “spike in discharge”? Are you referring to a voltage gauge that indicates a momentary drop in bus voltage during the event?

If so, does it last for the entire event? Or only a short dip in voltage?

Does the voltage drop to zero?

Chances are, you have an intermittant OPEN condition due to the cobbled up harness. This information will help to narrow down the potential culprits.

9

I go along with grounding the engine to the body/chassis. When putting in different engines, this is often disregarded until mysterious electrical things happen.