HELP! LS1 Trans am not starting
 

I have a 1998 Trans am ls1 auto with 98k miles and I jus had a audio system installed about two months ago. Got a sub amp and interior speakers and a new double din screen. My batter is a year n half old fyi. So just yesterday i was driving the car and it felt like it was shuting down. Lights dimming driving slow etc. so I parked it on my drive way. Next morning I go to start the car and its not starting and lights slowly dim away. So i thought it was the battery and tried jump starting it. It started then died 20 seconds later. So i instantly thought it was the alternator because of the extra power coming from the new audio system. Took the alternator out and noticed I had a bad belt. Bought a new belt and tested the alternator and surpirisingly the alternator passed 3 times in a row. Now i am stuck and do not know what can be wrong. Any help guys?

I had the same kind of issue on the VERY first day of owning an F-body (99 WS6), on the way home everything started to dim and I felt like it was losing power... Had to get my car towed literally 94 miles back home :o

Turned out it was the alternator on mine. - My Mechanic first thought, well this alternator looks brand new and tested for a bad ground and other things, still turned out it was the alternator.

I would see if you could get it tested or something :)

TTT

I got the alternator tested and it passed

If you start the engine and THEN disconnect the negative battery terminal, while the engine is still running....and it dies. Bad alternator. Don't trust the tests.

A basic PepBoys alternator will support a 427ci, A/C on full blast, at night with all lights on, idling, with a 1,000 watt amp thumping a 12" woofer.......my PepBoys alternator supported that for 10+ years without a single drop in power, zero dimming, nothing.

So don't go crazy thinking about super-duper special battery....totally not needed.

Go get another alternator...they take 15-20 minutes to change. If its not it...return it and tell them you got the wrong one and it doesn't fit because someone modded your car and it required a different bracket and different alternator. It'll work, they'll take it back.

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I agree with LS6427, he has always answered my questions and has been right :D

What kind of voltage is the alternator putting out while running on the car? Check it with no load on it then turn everything on, lights, blower motor, etc. This will only show voltage not amps. However you can have good voltage but no amps.

Check all your connections, grounds, etc.

Also make sure you are getting power to the alternator on the exciter wire and to the big wire on the back of the alternator.

The alternator may very well be good but you might have other things going on. Don't just throw parts at the car like others have suggested.

If you have an audio system you probably are using a lug style connector on the one or both of the battery terminals now so you can run the power wire to your amp. Make sure those are tight. I have seen the cause problems not being tight when you think they are.

Test. Don't guess.

I had the same issue. Alternator tested good, then decide to swap to one pulled from a buddies car that had been setting for awhile. Turned out both would pass but were bad. After my buddy decide to borrow one of my plug wires the car wouldn't start, went through a new battery, swapped alternator,etc and it ended up being the little red wire was pulled loose when he pulled the plug wire off. That was a few years ago, my 98 camaro did the same and it was the small wire on alternator again.