Alternator Draining Battery / Wont Start
Thread Starter
Cruising
Joined: Apr 2021
Posts: 13
Likes: 1
Alternator Draining Battery / Wont Start
Hello! I've recently just bought a 1991 corvette and it had been running perfectly for about a week until I decided to get it inspected. I had a mechanic look over the car to make sure it was mechanically safe and to have a new A/C unit put in it. Since the guy put the new A/C in it has not been able to start... I've looked at many forums and can't seem to get it started, I believe that there is partly a VATS issue as to why it won't start however the other night the brand new battery was drained while the car was off. The car also blew the starter and when it was replaced blew again! I had a 3rd put in and the battery disconnected so it cant blow again but what would be the reason for this? The mechanic said that he disconnected the alternator and the battery held its charge so what could be a possible fix to this? Since all of this I have had the car towed back to my house as the mechanic has not been able to fix it... is there anything I can do to get it started again and not have the battery drain? I've already ordered a workaround part for the VATS system but I still need a fix for the electrical part of things.
Racer
Joined: Apr 2016
Posts: 336
Likes: 93
From: San Antonio TX
A shorted diode in the alternator can be a parasitic drain on the battery. I don't know how a starter can "blow", and a shorted alternator diode certainly couldn't cause it. What is your level of mechanical/electrical expertise? Since you seem to have given up on your mechanic, I assume you want to give a try at diagnosing it yourself. Get a FSM and a voltmeter, follow the diagnostic charts...
Thread Starter
Cruising
Joined: Apr 2021
Posts: 13
Likes: 1
The starter has to be replaced like it's fried, not sure if I'm using the best words but hopefully, my point is getting across. My level of expertise isn't very high in this situation, I am a newcomer to the classic car scene and purchased this car as one of my first classics to try and work on as much as I can myself, however, I have a person coming out to look at it who has worked on it prior to me buying it which is why I had it given back to me as that mechanic also had stated that he couldn't figure out the problem on it. If the guy who comes out this weekend cannot help I'm looking to have it brought to someone who specializes in classic corvettes but my hopes are I can get it working before that becomes necessary. I would also like to add that the alternator was basically brand new when I purchased the car and wasn't having any issues prior to this so could it still be an internal problem? I will also certainly take your advice into account and look into buying what you told me to, Thank you!
Last edited by pgann91; Apr 28, 2021 at 08:29 PM.
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
If you take it by O'Reilly or your auto parts store of choice, they should be able to put an alternator test on it (quickly and for free). I wouldn't take it as gospel, but it could be helpful.
With a multimeter you could also measure the current the battery is outputting with and without the alternator connected. DMMs max out at 10A, but you shouldn't be pulling anywhere remotely close to that with the car and accessories turned off.
With a multimeter you could also measure the current the battery is outputting with and without the alternator connected. DMMs max out at 10A, but you shouldn't be pulling anywhere remotely close to that with the car and accessories turned off.
Instructor
Joined: Mar 2021
Posts: 189
Likes: 73
From: Christiansburg Va
You dont have to take the car there. Pull the alternator off and take it to the parts store. They have a machine to do a bench test that will verify operation, at least my local Autozone does.
Thread Starter
Cruising
Joined: Apr 2021
Posts: 13
Likes: 1
Thank you, I found the alternator wasn't the problem and there isn't even a battery drain so the mechanic must have left a door or hood open or something because I connected everything overnight and it was perfectly normal. I am now faced with the issue that my security light does not turn on what so ever and the car does nothing when the keys turned to the ignition. If you have any more information please share. Thank you.
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Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
The hood lights or the interior lights will definitely drain the battery in a hurry. Swapping all those over to LED is one of the quickest, cheapest, easiest, and most worth-it things I've done to the car.
Are you sure the battery is connected and charged? Only time I've run into that is a dead or disconnected battery. My next guess would be a bad ignition switch, but that's a total guess. I'd recommend getting a FSM and working through their diagnosis procedure.
Are you sure the battery is connected and charged? Only time I've run into that is a dead or disconnected battery. My next guess would be a bad ignition switch, but that's a total guess. I'd recommend getting a FSM and working through their diagnosis procedure.