Hi,

I have been trying to chase down an electrical problem that burns out headlights and damages alternator. My little beancounter brain get's overloaded with this stuff...

Symptom: When the headlights are on (w/ the car running), there is an intermittent, very sudden and noticeable brigtening of the headlights and gauge lights (and I assume all other lights for that matter). When I am driving the car it happens once in about 20 seconds or so.

It keeps happening until at some point the alternator goes bad. After the alt stops providing proper charge, the lights stop brightening, but, naturally, the car is not very dependable, as it can only go as far as the battery can carry it.

I just replaced (another) alternator, and it measure ~14v at the alt, and about 13.5 V across the battery terminals.

The battery is new as well, and measured fine when tested at Napa.

I have cleaned the battery-to-frame and engine-to-frame ground conncetions.

So, it seems like something is getting charged up and causes voltage spike as the charge releases?

The alt is a 90 amp alt, but the 12-gauge wire between the alt and horn relay measures only 45-50amps.

I am running MSD 6al.

Thanks in advance!

Pete

 

That is an interesting problem. Sounds like the voltage regulator is having a hard time. Since you've replaced the alternator, that takes care of that.

Hook your voltmeter to the output on the alternator and watch. Can you see the voltage change?
Almost sounds like a capacitor is charging and then discharging. JUst for grins, unhook your MSD and try it without that. Unless you have a killer stereo with caps inline for the thump, that's the only thing I can think of with enough cap to show the symptoms you are talking about.

 

Thanks TimAT. I do not have a killer stereo, just an old & tired cassette radio.

I do have electric fan and fuel pump. I measured the amperage of the hot lead that provides power to them and it measured about 13 amps.

Cheers!

pete

 

You do have the power feeds for the fan and pump (and MSD) right to the battery? or at the least to the battery post on the starter.

 

MSD box is connected to the bat terminal of the alt.

The fan and fuel pump are connected to the bat terminal of the starter.

Cheers!

Pete

 

Thank y'all who helped me to get the very frustrating problem solved and fixed. Still not sure if the issue was caused by one or combination of problems. Anyways, the problem is gone as a result of the following procedures:
- pulled a direct power lead (8gauge wire + 12 gauge fusible link) from the alt to starter. Now I get nice and steady 14 volts @ the battery, when the engine is running @ 1500 rpm;

- disconnected MSD box power lead from alt and connected it to the horn relay;

- removed a circuit breaker from the starter-to-horn relay wire and; replaced it with a fusible link;

- disconnected the (non-functioning) ammeter;

-attached a loose rear light ground wire to the frame.

Life is good!

Pete