When I drove my '82 Turbo out today, I noticed that on the run-down (when I let off the throttle to coast down to a stop), my stereo and voltmeter would frequently reset, as if they were turned off, and back on again. I didn't see any unusual reading on the voltmeter though to explain the sudden loss of power (was consistently reading 14+ volts at speed). Then after a little while, I suddenly lost all power to almost everything, including the stereo, gauges, and windows! I don't even know for sure if my taillights and blinkers were still working.

However, the engine was still driving fine in stop and go traffic and I still had power to an aftermarket circuit that I'd wired up to go on with the Acc-On position. This circuit is wired directly to the battery, and has a relay that's activated by an electrical signal from the Acc-On key position, so I must be getting power through that at least. But if I'm getting power through the Acc-On position, why wouldn't the stereo (which goes on in the same position) work as well?

At first, I was thinking maybe some kind of fuse blew, which would be a simple fix. But after awhile in traffic, electrical power inexplicably came back. This is certainly disconcerting and I haven't installed anything recently that would fiddle with the internal power like that. The only thing I've touched in the past weeks was to pull out a sparkplug for inspection and put it back in. Does anyone have any thoughts as to what is far back enough in the electrical system to disable so many systems, but then be intermittent?

I don't know if it's related or not, but when I went to the start the car (for the first time in about a week), the voltage was relatively low. So the car did sputter and struggle a bit to start up, and I pressed the gas peddle to help it fire up. Could some kind of voltage spike have occurred during this time to damage something and thereby cause the blackout?
Also, when I pulled into my garage after my errand, I heard this strange pitch/tone coming from under the hood, which also may, or may not be related. It sounded very much like a tiny siren tone coming from around the intake manifold area. It definitely didn't sound mechanical, and could be heard above the noise of the idling engine. However, I didn't have time to investigate that further before going to work. Do you think any of this could be related to the bit of knocking I experienced when I tried having it dynoed last week?

Oh lordy, this certainly puts a damper on my day...

 

Did you check your battery terminals? It sounds like a + wire is grounding somewhere, or one of the battery terminals is loose / corroded.

 

Nope, it's not the battery or terminals. The terminals are practically new, gold-plated car audio terminals. I was suspecting a short as well, but that usually blows out fuses and shouldn't fix itself like it did.