WJ battery draining intermittently...

[Dingleberry]

Hey guys,

My granddad has been trying to fix a WJ back in the UK and the battery will drain intermittently... doesn't do it all the time, only sometimes overnight etc.

Are there any known issues with the WJs (with 4.7L engine) that could cause the battery to drain flat every so often?

Cheers!

[esi]

I've noticed that my WJ will turn its headlights on for 1 second to 1 minute while its shut off. Depends on the night sometimes it does it sometimes not. But its only if the headlights are set to auto. Could be a possible cause to draining a battery. Other than that could try cleaning battery posts and checking battery condition.

[cLAY]

Check the brake lights. My moms Buick drove me nuts for months with a mysterious battery drain. The brake switch was misadjusted and occasionally would allow the brake lights to stay on after being parked. Didn't figure it out till she came out of the mall one day and noticed it when she went to put stuff in the trunk or boot in your Granddad's case. 

[WhiteOut]

Check the brake lights. My moms Buick drove me nuts for months with a mysterious battery drain. The brake switch was misadjusted and occasionally would allow the brake lights to stay on after being parked. Didn't figure it out till she came out of the mall one day and noticed it when she went to put stuff in the trunk or boot in your Granddad's case. 

This.

The ZJ does it when its cold out.

[JadeMonkey07]

If you get out your volt meter you can check the draw. Put it on amperage, disconnect the positive lead and use the meter to make the connection between the two. It shouldnt read more than .01 mA once its at rest(give it a few min, some take up to five) make sure doors closed. If theres a hoodpin put something on it to keep it down. You gotta hang around and see if its spiking. Most vehicles sit somewhere around .002 mA. If it is much higher than that, start pulling fuses one at a time put each one back after verifying the reading. This can help you narrow down at least what area is causing it.

If you've got time tonight I'm having a garage night with a bunch of boys in cochrane, i can take a look for you.

[Dingleberry]

If you get out your volt meter you can check the draw. Put it on amperage, disconnect the positive lead and use the meter to make the connection between the two. It shouldnt read more than .01 mA once its at rest(give it a few min, some take up to five) make sure doors closed. If theres a hoodpin put something on it to keep it down. You gotta hang around and see if its spiking. Most vehicles sit somewhere around .002 mA. If it is much higher than that, start pulling fuses one at a time put each one back after verifying the reading. This can help you narrow down at least what area is causing it.

If you've got time tonight I'm having a garage night with a bunch of boys in cochrane, i can take a look for you.

Since this is for a customer/friend of his, and the problem is intermittent, this is easier said than done.
He's been a mechanic for over 50 years now so I'm sure he's already taken steps such as this to determine what it could be, however I will be sure to let him know about the brake light theory.

[JadeMonkey07]

Iv always found the problem using this technique, electrical repair is all i did for a few years. Mechanics sent us the stuff they couldn't fix, not to demean his experience.

[Dingleberry]

Its just the situation he's in, he doesn't own the vehicle so he doesn't have access to it 24/7 unfortunately.
When he does try to diagnose it, the trouble doesn't appear, gotta love Jeeps lol!

[JadeMonkey07]

Its just the situation he's in, he doesn't own the vehicle so he doesn't have access to it 24/7 unfortunately.
When he does try to diagnose it, the trouble doesn't appear, gotta love Jeeps lol!

Yeah those are always fun. So hard to replicate the situation sometimes