volt meter and battery light


Asked by tennisshoes Mar 05, 2013 at 10:27 PM about the 1996 Isuzu Trooper 4 Dr Limited 4WD SUV

Question type: Maintenance & Repair

Volt meter reads normal, about 14 volts at idle and battery light is off, if you accelerate like climbing a slight hill or passing on the freeway the voltmeter drops to just under 12 volts and the battery light comes on, if driving at night you notice the lights also dim, back off the gas and everything goes back to normal. I was told it was the alternator so I replaced it and all of the belts, same problem, took out the new alternator and had it tested, and it checks out very good, the guy told me that this is a ECM controlled alternator and that might be the problem.  I put the alternator back in and checked wiring up the side and to the main plug in the engine bay, didn't find any problem there.  Anybody got any ideas?

9 Answers

Not Active

the voltage regulator is part of the alternator...maybe you got a dud. It's not unheard of.


I think the troopers had a blue relay or something tied to the air cond. relay and one is for charge , look at relay box

1 out of 1 people think this is helpful.
Not Active

..wow kinda guru-ey, just like the genie...

King Hostile

Your ignition modules(units the plug wire come from) could be failing and forcing the battery to supply the missing voltage during acceleration, or under load.


First thing that came to my mind is a broken wire or bad electrical connection. When the engine is under load, it moves in the mounts, pulling on a wire and the circuit opens. - Give the wiring a close look before throwing more alternators and ECU's at it.

2 out of 2 people think this is helpful.
Best Answer

I had a similar sounding problem once. What I found was the engine ground strap was broken and as the driving torque of the engine increased like climbing a hill or accelerating, the engine would lift just enough to loose the ground. This sounds impossible but ground the engine to the frame & engine to the battery and see what happens.

1 out of 1 people think this is helpful.

Thanks for everyone that responded to my problem. The problem was the ECM, for some unknown reason it would put the alternator into economy mode during acceleration. ECM replaced problem is gone. Happy Trails

5 out of 5 people think this is helpful.
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please click 'mark helpful' for those of us who you thought were helpful. I gave you ten points....just 'cause I can~

1 out of 1 people think this is helpful.

Since the alternator is control by the ECM find out which wire from the alternator go to the ECM. Cut that wire so the ECM does not control the alternator anymore. My friend is a master mechanic and did that to his customer car. No more battery light and everything is ok

1 out of 1 people think this is helpful.

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