Hello all,

This is my first post, so please go easy on me and if I am in the wrong area direct me better. Thank you.

My girlfriend's 1990 Jeep XJ has been killing batteries. 2 batteries went bad and could not hold a charge. This third one is doing about the same where after a day or two of not driving it, it'll be completely dead. The voltage will read about 8 or so on my DVOM.

When started and running, the battery voltage will at about 14.88 or so. Isn't that kind of high?
This is the original alternator and this jeep is kind of a time capsule. It has 80k on it.

The battery cables were upgraded to 1/0 gauge with a inline fuse.

The driver side door switch is missing and there is just a hole, so when the driver side door is opened no lights come on (may be a clue). All electric seats don't work, and the electronic door locks don't work, but once in a blue moon they'll work. I hadn't checked a wiring diagram yet, but I'm thinking there is a short in that circuit.

The Jeep also idles like crap. It also sounds like there is a vacuum leak coming from the EGR valve. This is probably contributing to the poor idle.

I have not done a voltage drop test yet.
I have done a parasitic draw test on the negative side of the cables and I get 0, which is also very strange. I don't even get 0.03 or nothing. I will check the positive side.

I have seen people adding an external voltage regulator on these Jeeps, what is up with that? Is there a voltage regulator in the alternator? I think there is one in the ECM. Do you guys think the ECM is toast?

Thank you for your patience and time.

Agree on your idea of vacuum leak vs. idle quality.

14.88 is normal when the battery is drained, that is the ECU trying to get it full again as soon as it can. There is certainly a draw when parked to do as you describe. Are there any add on circuits at the battery posts? People often add winches, CBs, and other such stuff straight from the battery and they don't always use best practice techniques.

You may want to get a battery charger to put on it over night while you work this out to keep from burning out batteries, just don't drive away with it connected.

Keep after it and we'll get to the bottom of it.

My car charges at 14.95 when cold but at running temp it charges at 13.50 . so does your jeep lower the charging when warm ? I think you have a draw on the battery that is killing it . you are going to check for something that is is shorted or stuck on .

Thank you for the response!

Other than a huge vacuum leak, perhaps fuel injector upgrade would help a lot and checking the time and chain. I bet it is fine though.

As far as upgrades and changes on the vehicle. This vehicle is bone stock electrically. The only mod that was done to this was the thicker battery cables and military battery posts.
The old original bendix braking system was removed for a more desirable dual diaphragm brake booster. So the wiring harness for that is still there but, this electrical drain has been there ever since she got the XJ. HAHA, yes definitely not driving away with the charger.

Also, do you guys think that the electric seats not working and the electric door locks not working intermittently may have something to do with this?

From everything you guys have said so far it sounds like there is a parasitic draw coming from somewhere. The Neutral Safety Switch did blow on this vehicle, I'm wondering if there is a shared harness for all of this to back probe.

The door locks and the seats are hooked to battery power , the power windows are hooked to key switch power . that would be a good place to start looking for the power draw .

I used to have a car in Michigan where rust had caused the door locks to randomly lock and unlock the car while it was parked. The locks had their own fuse so I 'fixed' the problem by leaving the fuse out and manually locking. If there is a fuse just for the locks, or if it is shared and you can do without those features for a few days of testing you could pull that fuse. Then you could narrow down to what circuit you have to work on.

The ECU in this model-year has no interaction with the alternator whatsoever. The voltage regulator is part of the Delco Remy CS-series alternator.

In regard to a suspected drain, start with this. Using a clamp-style amp meter or an in-line ammeter capable of measuring direct current, start by pulling the cube relays next to the distributor coil, one at a time, with the ignition off. Eliminate the B+ latching relay before proceeding.

Your other issues with items not working are likely faulty grounds… except for the door jamb light switch, which you indicated is missing.

Fair enough, but you will see the exact same behaviour from a stand alone voltage regulator. This is how my 76 Volare charges.

If the wire for that missing door switch is not properly stowed it could cause a drain if it is making a poor connection inside the jamb. In unlucky conditions this could cause a drain small enough to not visibly light the overhead bulb although I don't think that would be enough to kill a battery over a single night. I've seen this in the rust belt where the wire is sitting in salty muddy grime inside a door sill. Probably not your issue, but sharing info is what makes us human.

edit: These days FLIR cameras are a good tool to search for some kinds of electrical faults such as a partially on incandescent bulb. If you know someone who has one it might be worth a beer and a pizza to get them over for an afternoon or evening.

So I know this is an old post but I appreciate closure to threads and hopes this helps someone in the future.

So I found that the circuit that goes to the power seats locks front and rear are on one circuit. There was a short underneath the driver seat. I think someone in this section said that it's all on one circuit.

Just cleaned some connections, made some new wires and bam no more parasitic draw.

Hope this helps

thank you!!