Hey guys. I started this weekend on a mission fix the car again :D. It's an aussie built '78 GM 6cyl carby motor. I have a fluctuating volt meter in the dash. And when the electrical system is under load (ie high beams/radio/heater blower/cig lighter/wipers) the electrical system almost dies. The wipers come to a stop. The motor still runs ok, maybe a slight stumble, but otherwise ok. Should also mention when I jump on the brake pedal 4 or 5 times quickly, the motor stumbles and stalls.

When I loaded up the electrical system I only had 12.63 volts comming from the (external reg) alternator. At idle in gear with no load I could only get 13.88 volts. I also checked the battery State of Charge as mentioned here http://www.uuhome.de/william.darden/carfaq4.htm#measure
and came up with 12.32 volts and puts it somewhere within 50-75% SoC.

As a process of elimination I
-Replaced the fan belt. Good tension.
-Replaced the voltage regulator. No change.
-Checked the earths with a voltmeter (earth to engine and to body)
-Checked points, plugs and leads
-Checked for worn vacuum hoses
-Changed the battery from another car, same multimeter results (but I didn't do the electrical load test)

Just thought I'd throw this out there and see if I may of missed something very simple. I'll probably end up taking it to a shop tomorrow.

TIA, Chris

Have the alternator tested to make sure it's putting out proper voltage.

Sounds like maybe the symptoms of a bad connection somewhere.
What vehicle is it?

Its just an old '78 holden with a stock straight 6, 202ci, points and carby motor. My daily driver.

I'm gonna take it down to the shop this morning and test the 3 month old alternator. Maybe they'll find something stupid I missed. I've searched the forums and found similar posts, checked/replaced everything I could in a day. I'll report back tonight.

Got the problem sorted out today. For those interested here's what I learned today at the shop:

1. The fluctuating voltmeter in the dash probably has a loose earth or something. Thats what's making it go all over the place. Not worth fixing.

2. The auto elec did a load test using a machine hooked up to the battery. Battery no good. Battery replaced. No more slow wipers when the headlights are on.

3. My multimeter is out by .2 of a volt. The reg is actually putting out 14.08 instead of the 13.88 I thought. Quite normal for a 25 year old electrical system.

But thanks to those who replied with suggestions.