Charging Problem

[ahuster]

I'm having a charging problem on my 93 MTX. The battery light on the dash keeps flashing on and off and the lights dim and the blower for the AC surges when it comes on. I had the battery and alternator tested at Advanced Auto Parts and both tested good. So I checked and cleaned the battery terminals, ground wires, and alternator connections to no avail. I'm wondering what els to look for or check?
Any suggestions?

 

[Bizzy]

There's a short somewhere. You may want to have the alternator and battery rechecked somewhere else, just to rule out human error when Advance did the check.

Check for things like light bulbs that don't go out when they are supposed to, like in the trunk, under the hood and in the glove box.

Then you have to rule out things that have changed from before you started having the trouble and now. What was added or removed? Sometimes aftermarket head units have a demo feature that will continue to run after the car is off which can run down your battery. Do you have an aftermarket amp? Is it run directly to the battery? Small things like that.

Also, I had a similar problem with mine not too long ago. I have an aftermarket battery clamp on my positive terminal. While it was holding tight to the battery, the part that crimps the wire to the clamp was working its way loose. If you have a similar setup, this would allow intermittent charging depending on the connection at that particular moment.

I offer only simple things to check. There are others who may suggest more useful things for you to check.

 

[projectSHO89]

There's a short somewhere.

I have to present a opposing opinon to that of the boss.

Short circuits are typically manifested by blown fuses, circuit breakers, smoke, or sparks in any combination.

Your symptom is more likely of a defective/high resistance connection or wire. Ground connections are infamous for this. Also of concern in your particular vehicle would be the output wire of the alternator and it's connections back to the battery positive terminal. A bad connection or wire will cause voltage to be dropped across the connection and will definately cause your lights to dim. The drop in supply voltage will disrupt the BSC module's ability to regulate blower speed and will actually cause it to increase its speed, unless it is already running at maximum speed. According to the schematics I consulted, there are fusible links in this circuit. That means splices that may have corrosion or a fuse link that is "intermittent".

If you have the opportunity to catch the car "in the act", hook a meter across the alternator B+ and the battery positive terminals while in failure mode. A good set of connections will show almost no voltage across the set of connections. If there is a high-resistance connection, it will cause a voltage "drop" across the connections that will be proportional to the current draw from the alternator. As your lights are dimming, I would be on the lookout for any voltage drop of more than 1 volt although the desired value would be several millivolts (depending on current).

Steve

 

[Bizzy]

projectSHO89:

There's a short somewhere.

I have to present a opposing opinon to that of the boss.

wink That's why we all work together. I was thinking "Sounds like..." but didn't type it.