Interesting Electrical/Charging Issue Options

[GregAmy]

1974 2L 914. "Driver" condition, way far from concourse, but drives well. I've noticed from the beginning a relay clicking under the dash; at first I thought I left my turn signal on, but it's not. It didn't seem to bother anything so I ignored it.

Couple nights ago I drove it for the first time at night. It was then I noticed the "gen" light was glowing very faintly, and at idle I'd hear the click and the light would get brigth(er), then slowly dim. Then it would click again, get bright(er), then dim.

I've also noticed from the beginning that the voltmeter would show 13+ volts normally, except when I stepped on the brake; when I did that it would go below 12. Same thing happened when I flipped on the lights. Strangely, when I did either, the clicking would stop...

Today I did some basic troubleshooting. Had my assistant sit in the car and I measured voltage directly at the battery. At idle, center console gauge shows ~13v, VOM showed 13.75. Good. Asked Vanna to step on the brakes; gauge showed ~11.8V, battery showed 13.4. Asked her to turn on headlights and stay on brake; center voltmeter showed ~11.5, battery had 12.3-12.5. Asked her to rev it, battery voltage got up to ~12.7.

So it really doesn't sound like I have a charging issue, it sounds like there's something going on under the dash.

I'm gonna guess you're gonna tell me it's a ground under the dash. But can you offer where I might find that? Or where I can run one to supplement it? The battery (from a Miata) has been moved to the rear trunk; it's positive cable goes directly to the starter and its ground to the ground stud under the rear trunk. The ground strap from that stud to the transaxle is very good, I've removed, cleaned, and re-attached it.

Car seems to be running fine, starts, drives, charges. I'm just looking to get accurate readings from the gauge and to stop that clicking...

Thanks!

Greg

[Mike Bellis]

Sounds like you are chasing 2 different problems.

Clicking is most likely the brake circuit. Either check the switch at the e brake handle or push the reset button on the master cylinder.

The voltage drop you see an the gauge is mostly due to age. All of our chassis grounds are rusty and corroded. The ground plane of your car used to be the entire unibody. After 40 years, it is spot welds and steel panels. The factory volt gauge should have a dedicated wire from the battery but it shares with all the other accessories. Clean your grounds and the reading should improve.

The other factor is corrosion on the old wiring harness. Even if it looks good, it's still 40 years old, on a design built for a ten year life span.

[GregAmy]

Gen light doesn't come on when the headlights are turned on?

Nope. Behavior is the same, with or without additional load.

Sounds like you have a "soft short" in the flasher circuit....You could tell which side of the alt light the drop is on by checking the voltage across the light when it is lit.

Good point. I shall make that my next troubleshooting step. But note that since the prob goes away with the flasher relay removed, I suspect it's going to be on that side, downstream of the relay.

Clicking is most likely the brake circuit. Either check the switch at the e brake handle or push the reset button on the master cylinder.

Not sure why you say that? It's definitely the flasher relay that's clicking. When I remove the flasher relay the clicking stops and the gen light stays off.

The other factor is corrosion on the old wiring harness. Even if it looks good, it's still 40 years old, on a design built for a ten year life span.

Yup. If I can find the resistance circuit, I can repair/replace it.

GA