charging system issue

[torker]

No not an EV but electrical in nature anyway. I have a 95 Geo Metro,bought for my son to drive and it has stopped charging. I have changed the alternator and it still won't charge. After checking continuity on grounds and between the alt. and pos. cable at battery and making sure I have key on voltage at the plug on the alt. for excitation I am stumped. I took the new alt. off again and took it back to get checked just in case it died right away but it checks good. One strange thing is that the battery light does not come on. It comes on with the key on and then goes out as soon as you start it. The book shows hot going to the light and then to the other term on the alt. connector When I check with the key on I have 12 v at both term. of this connector, there is 3 term.on the conn. and alt but only 2 wires not sure about the third.

Like I said I am stumped. I can charge the batt. to 13.2 it settles back to 12.7 it starts and runs the car fine but drops to 12v right after starting. Also this car has auto headlights and when you plug in the alt with the key on a relay shuts the headlights off till you start it. Seems normal. I've also pulled every fuse and relay except FI and IGN. and started it. Thinking something was drawing major amps.. Sorry so long.

Anybody got any ideas for me I want this rig on the road again..

 

[dnmun]

it may have an external voltage regulator to excite the field. that may be your third wire. most newer alternator have the regulator built in, don't know if that one does.

 

[torker]

Yea it shows a rectifier built in I think. All it shows on the charging system print is the alt and 2 wires, one straight to ign. voltage and one to idiot light and then ign. voltage. The alt. and connector have 3 matching terminals but only 2 wires?? And of course the large wire going to the pos. batt post. It is separate, not part of the connector. Strange that the batt. lite does not come on. I'm missing something, just not sure what to do next.

 

[dnmun]

is it the ground wire?

 

[dogman dan]

Bad alternators always kill the battery. You nearly always have to replace them together. Try a new battery. Even if it is new, if it ran for very long on the old alternator, it may have killed it fast.

 

[dak664]

It's easy to find a large current drain if that is the problem. The poor man's current meter is a compass. Amusing to use, but the surrounding metal affects it so you have to hold it near a wire and look for deflection while connecting and disconnecting the battery. With an clamp-on current meter you just connect the battery and follow the high currents.

 

[spinningmagnets]

if you can charge the battery to over 13V on the bench, its probably still good (no sulfation or holes in thin plates from deep cycling). An old guy once had a volt gauge hooked up to his car under the dash and I asked how that helped. He said when it reads 14V the alternator is working, when it reads 12V the car is running on the battery. So,either the alternator, voltage regulator, or fan belt is bad.

Find the VR and check the input/output.

 

[torker]

This one appears to be built in to the alternator. I just wish it would quit raining. my garage is full of bikes etc.

 

[EMF]

With the car running, disconnect the positive cable on the battery. If the engine dies, the alternator is bad. If it continues to run, there is something wrong with the battery.