I've got a high Voltage at the battery, while my MJ is at Idle.

[Lazarus19]

I'm aware that this is probably a fairly simple problem, and sorry for wasting anybody's time. 

 

I've got an '88 Base model. I've been doing minor fixes here and there for a while now. Around may of this year I put a new battery in it, I replaced a few things causing leaks, yadda yadda. 

 

I went to start it up, and the battery was dead. It had been a couple months since I started the truck last, figured it needed a jump. Took about 30 or more minutes for it to catch and start up, after which my idle was a bit rough, but it was rough prior to this. I have a few other problems I may come back to the forums for further questions, but for now let's stick with my current one.

 

I went to start it up a weeks later and had the same problem. Dead battery, long time to jump it. I run a volt meter to my XJ at idle, had 13.5(ish) volts. Switched that battery into the comanche, ran at 14.6 volts. Best I can tell, that is high. Figured my alternator was going out. 

 

The next morning, this battery wouldnt start my XJ, meaning the MJ killed that battery in the 20 or so minutes it was running off of it. I feel like it is definitely my alternator at this point. I just had it tested, and my alternator passed 4 tests at auto zone. 

 

I'm not entirely sure what my next step is? I figure I've got an electrical problem, my best guess is the radio that was done poorly by the previous owner, maybe a "constant" wire is hooked up wrong? Idk. But i had this vehicle running last year, without this issue, so it's a relatively new problem. Any help?

[Ωhm]

3 minutes ago, Lazarus19 said:

Switched that battery into the comanche, ran at 14.6 volts.

This voltage is good.

Check your glove box light/switch.

[Dzimm]

Your alternator outputs 14.6v, that's normal.  You've got a constant draw somewhere so you'll have to start searching.  

[Pete M]

welcome!    Be sure to add in your truck's specs to your signature.  

 

 

[Warren Mohler]

if water level is OK use a hydrometer to test each cell if one or more cells are lower than the rest I would get a new battery, alternators are not meant to charge DEAD batteries just maintain good ones

[yxmj]

Voltage is not too high (I would be happy all the way to 14.8)

Here is an easy test

Pull off the -ve cable .....put a test light in between the cable and post......if it lights you have a draw (drain)

you could now start popping out fuses one at a time until the light goes out....that circuit will be the culprit

 

I have never done it with one but this test should also work with a multi-meter....it would be better I assume as you would not only see the voltage draw but you (if your meter is able) would be able to read the current as well (how much draw) 

 

I should add that you should try your best to shut off everything and make sure your doors are closed........and pull the bulb on the hood light if equipped