The Stovebolt Site Forums The Shop Area The Electrical Bay Sometime spike occurs when applying brakes

On my 1965 C30 truck, sometimes (not every time) I receive what I assume is a spike in the electrical system when I apply my brakes. It will occur at least once in a five minute trip, but I can hit the brake pedal a dozen times without any issues.

This spike will knock out the radio, thus resetting everything. I have one of those new radios where one power lead goes to a full time positive to keep the memory and the other to a keyed switch. I also believe this spike blows the heater fuse if the heater is on.

Where should I start to troubleshoot this issue? Has anyone else run into this? Is this a grounding issue? I just remembered that the spike also occurred (not all the time) when I put on my day-time running lights.

I hate electrical issues... Can anyone help?

You're probably experiencing a momentary dead short somewhere in a wire harness that causes the alternator to go to full current output to meet the demand, and as the short corrects itself, the current surge has to go somewhere. It picks the lowest-resistance path available, and that's probably the heater motor if it happens to be running at the time. The sudden loss of voltage as the short occurs is what's killing the radio memory. Since the speed of electrical current is theoretically the speed of light, it doesn't take long for a surge to travel all over the vehicle at 186,000 miles per second.

Start your diagnosis by doing an inch-by-inch physical inspection of the wiring harnesses, looking for a worn spot in the insulation that's contacting the frame or body intermittently with one of the big, heavy-current conductors like a battery cable, alternator output wire, main voltage supply to the ignition switch or fuse block, etc.
Jerry