I have a '75 1.8L that seems to have a charging problem. The battery was recently replaced and tests at 12.2v. The alternator was replaced about 6 years ago and when tested checks out at spec. So does the voltage regulator. The headlights were just replaced with LEDs which are great and draw less current than the old 100w bulbs and really light the way. The alternator drive belt does not squeal but I do smell burning rubber occasionally. Without any load on the electrical system the volt gauge reads 13v consistently at speed and maybe drops to 12v at idle.

Here's the problem... when driving with the headlights on the volt gauge barely registers 12v and is on the discharging side. When stopped at a stop light at idle with the headlights on, the volts drops to 11v. If I use the turn signal while stopped and have the lights on, it drops to nearly 10v. The battery is seriously discharging here.

This has been a persistent problem for some time, but has become exacerbated since I recently moved to SoCal where stop and go (mostly stop) traffic is a fact of life. Has anyone experienced this problem or have a suggestion?

1st, did you replace any dash lights with LEDS. If you did the ALT light, it will not charge. This would be the easy answer. Other than that, it's the battery not holding a load, or the alternator needs some attention. It could be the alternator and or the harness. I'm questioning the harness as it has rubber parts on it??
Thanks my take.

57Lincolnman,
I have the same problem on my '75, sometimes my gauge registers that the alt is charging, sometimes it reads that I am discharging. I spent 10 bucks on a voltmeter that plugs into the cig lighter socket (cellphone charging port for you young ones!). The alt now reads that it is always above 12.5 volts, so I don't trust my 42 year old VDO meter. If you still are unsure about your charging system, put a voltmeter across the battery cables and and compare your VDO meter to your tester.
Just my $0.02.
Phatnine11

I too have the same issue. Sounds like it might be very common for that year. The plug in volt meter is a good suggestion. I have one additional electrical problem, once pulling on the headlight switch to parking lights or full headlights on, the volt meter pings to the left and the temp senor pings to the right to full hot. It seems l have a short somewhere. Any suggestions on where to start first or how to break down areas to test for correct continuity? I don't have LED headlights the rest of the lighting system is stock.

They all do that unless you run a dedicated + from the battery to the gauge.

I'm not sure whether to believe you or think you're pulling my leg. I know my car has been like that since I bought it 30+ years ago, but I can't imagine the Germans would accept that kind of blatant fail.

The way the gauge is wired into the electrical system was done more for ease of manufacture and low cost than for accurate measurement of the state of the charging system.

In other words, they all do that. (Except possibly if all of the electrical connections are absolutely perfect, which probably lasts all of a half-hour.)

Treat the gauge as "entertainment". Or get to know how it behaves and then only pay attention if the behavior changes. To get an idea of the actual health of your charging system, use a volt-meter across the battery posts themselves.

--DD

Thanks Dave. At least I can take that off my to do list of maintenance issues for the car.

I got on tonight to see what was with my '75 running at 13amps, idling at 12 and not charging...

I'm going to clean up my battery connections tomorrow, then test out the alternator...

Thanks to all those who posted above! Good timing!

Be suspect of the alternator harness and voltage regulator. Check the bottom of the relay board for missing tar.

Now if just had a working cigarette lighter... thanks for the suggestion. I will check this out.

If you have a new battery, and after driving for a while, you're reading 12.2V on the battery with the car shut off, then your alternator and/or voltage regulator and/or alt harness and/or alt light (etc.) are bad. A fully charged battery will read 12.75V. Not 12.6, or 12.5, but 12.75V When the car is running, you should be reading at least 13.5V to 14V.

The link below describes all of the tests you should do to identify which part(s) of the system is(are) faulty. I strongly suggest to anyone who is working on their charging system to read the info at this link in entirety. Good luck.

http://www.ratwell.com/technical/ChargingSystem.html