Already searched this... Help please.
 

I have a volt gauge plugged into my cig lighter. Normal driving conditions it will spike to 15.8 while just driving. No load. When i turn the subs on instead of the volts dropping when the bass hits it jumps to 16.2. Maybe regulator? I just bought this alt. i am scared that i will mess something up by letting this continue without knowing the problem.

regulator is in the ecu. you might start by checking the connections, at the battery and alternator

I will sary there. Thank you.

*start

I had the same issue a few years back and it caused $3,000.00 worth of damage (boiled a battery, fried the ABS module, power windows, etc). You need to stop driving it and pull the alternator and get it tested and rebuilt. Or get a new one.

It's not a common issue, you are only the third person I have ever heard of with the same issue. It will get worse with time.

thanks for the help 9krpmrx8. i took the car down to have it tested. it passed due to it did not act up at the time of testing. i have been driving my eclipse due to i was scared of causing future issues.. i want to drive my baby. thanks for the heads up.. if you dont mind me asking what alt are you running? where is a good place to get one. this is my 2nd one within a year from advance. oem is like $600.00. the part store basically tells me i am shit outta luck on warrenty due to it tested fine.

Ok, so we took the alt to a electrical guy to have tested and rebuilt. He tested it and it test just fine, says it puts out more that 110 amps for the car and regular 14.5~ volts. He did not want to raise the amps in it as to mazda said that would hurt the car. Ok, so im convinced the alt is good after about 3 different test. Still doesnt explain the voltage spike. Anyhow we go home and reinstalled alt and not im not even getting 12 volts. Will be rechecking connections tmrw again. But bottom line the voltage spike is most likely not fixed. I hear and understand the the voltage regulator is with the PCM? If this is true is there any way to have it tested? Or do we need to drop the 200+ on new PCM and hope for the best. The sound system has not been connected since we realized this was a issue. Also I did use a direct volt meter on alt this last time and its only putting out 11 volts and that what gauge in lighter reads as well. I know most will say bad alt, as to this may be true lets not rule out the regulator that tells the alt what to put out. I mainly need help on how to test these things or another direction to go in.

Thanks for help!
BTW this is husband. lol