AMC Eagle Den Forum

The Mighty 258 => Engine Electrical Systems. => Topic started by: BuckeyeEagle on September 27, 2015, 08:35:27 AM

Title: Battery light on without key?
Post by: BuckeyeEagle on September 27, 2015, 08:35:27 AM

Sorry if this has been asked/answered elsewhere - I couldn't find it posted, but this was a tough phrase to search for. When I picked up my '82 wagon this past Friday night, I put a new battery in just to drive it up on the trailer (PO had said the alternator was bad). I disconnected the battery for the trip home then reconnected to back it off the trailer. I noticed that the battery light came on even though the key was not in the ignition. In my excitement to pick it up I missed this initially.

I found some parts of the TSM online and it sounds like this indicates an alternator problem, which I was planning for, but is there anything else to keep an eye out for as I get into it? Does the battery light coming and staying on without the key point to any other electrical components/problems to look for? I'd hate to get the alternator done then realize I missed something else.

Thanks! 

Title: Re: Battery light on without key?
Post by: txjeeptx on September 27, 2015, 11:54:25 AM

Until you have the alternator tested, its difficult to determine if that is the only problem to suspect. I would either take the car to an auto parts store that can test the alternator in the car or pull it and bring the alternator to them. There also may be an electrical rebuilder in your area that specializes in alternator, generator, and electric motor rebuilding. They can be more helpful than the auto parts store personnel when it comes to figuring out a problem.

I would also look into the starter solenoid wiring to make sure a lead has not been placed on a wrong post, and the ignition switch under the dash on the top of the steering column may also be a place to check for miswiring or a bad switch. Finally, if there is any aftermarket audio equipment, lighting, or an alarm/kill switch installed, there may be a power lead that has been miswired somehow.

It is most likely the diodes in the alternator have failed and are allowing current to flow and drain the battery while the ignition is off. You'll know after getting the alternator tested.

Title: Re: Battery light on without key?
Post by: BuckeyeEagle on September 27, 2015, 11:56:21 AM

Thanks! Appreciate the info.  There is an aftermarket stereo, so that's a place to check.

Title: Re: Battery light on without key?
Post by: eaglefreek on September 27, 2015, 04:13:32 PM

I had that issue a few years back and it was a bad diode in the alternator.