View Full Version : Automobile Charging System Problem

Jeffrey Makiel
07-18-2008, 9:05 PM
Our family collectible car seems to be running off of its battery instead of the alternator. The amp guage is negative and gets worse when an accessory (headlights, blower, etc.) are on regardless of how fast the engine is reving. The voltage is the same for when the car is off or running.

So far, we changed the alternator with one that was rebuilt by a professional shop, installed a new voltage regulator (which was mounted on the firewall in lieu of being inside the alternator), and installed a new battery. Also, the cables from the battery are very clean and the ground connection to the engine block is clean.

This is one of the reasons why I prefer woodworking these days. :D

Does anybody have any suggestions?

Jeff :)

Ken Herold
07-18-2008, 9:31 PM
Any chance that the gauge is incorrect?

Tom Godley
07-18-2008, 10:04 PM
You do not say how old the car is -- but -- if the car was supplied with an alternator new and it had an internal regulator it should have been rebuilt with the regulator as supplied. I have run into problems when changes are made

An alternator will be able to supply the power needed at idle -- this is why they moved to an alternator from a generator (DC)

Other things can be causing a problem - a bad ground can often cause problems. I have also run into headlights that had internal shorts (rare)

The charging system is very simple -- not many places to cause a problem.

Keith Marben
07-18-2008, 10:11 PM
amp gauges require all the power for the car to be run through them. It might be the positive lead that runs through the gauge, or the gauge itself. Old AMC made jeeps had amp gauges that were notorious for starting fires.
Something to check for, especially if it starts hard, runs weird.

Lance Norris
07-19-2008, 6:07 AM
It is also possible that your newly installed alternator is defective. Dont discount this possibility. It happened to me and I almost pulled my hair out trying to figure it out. Have it tested at a local parts dealer. Its a simple test.

David G Baker
07-19-2008, 7:56 AM
I had Pep Boys in California change out my alternator. Two batteries later and three different rebuilt alternators I took the car to a local repair shop. Took them 5 minutes to diagnose the problem and fifteen minutes to change out the Pep Boys alternator. The alternator had a built in voltage regulator and the alternator was located near the exhaust manifold that heated the alternator and fried the voltage regulators inside. The local shop installed a Bosch and as far as I know the alternator is still working.

Pete Simmons
07-19-2008, 8:43 AM
Step 1 - Check voltage at alternator output when running it should be close to 14 volts.

If not a volt or 2 above 12 volts

goto step 2

Step 2
Disconnect the field lead off the alternator.

Jump +12 volts to the field post on alternator - with engine running (be VERY careful not to get you tie or the wire caught in anything that is moving!!!

This will force the alternator to max output - you should hear the engine take on the extra load. Look at amp meter if it is working.

Let others comment on how wise/safe it is for you to do step 2.

If you are the least bit uncomfortable working around moving parts DO NOT ATTEMPT - take it to a pro.

Steve Clardy
07-19-2008, 3:21 PM
Check all wiring connections.

I've had bad connections before.

The check by Pete is spot on