93 Sahara w/12v on the body, and each side of 3 fuses, WONT START and nothing works

[beepbloopjoop]

I killed it as I was pulling the incline into the garage, and it wouldn't restart.

Nothing worked but the Parking lights which are factory in the front and LED in the back. If I switched on the headlights they all went off.

No blown fuses under the hood, or in the passenger compartment, however, three of the fuse connections are reading 12v on both sides of the terminals with the fuses pulled. Those are the "acc lps", "ign lps" and the big metal fuse-like thing on bottom center that is claimed to be for windshield wipers.

I tested each side of each fuse holder, and these three were the only ones that showed 12v on both sides, so I thought that can't be good.

If I connect my cheapo multimeter positive on a rust hole in the floor, and negative to the battery, it shows ~12v, so I think that means I have a short to ground. I assumed this meant it was in some circuit that was shared by all three of those fuses, but I'm not sure that makes any sense and nothing's turning up.

I have tried leaving the multimeter hooked to the body in this way, and jiggling bundles of wire here and there, pulling others, and disconnecting every connector that I can, just to look for a change, and nothing's changing. I unhooked the lighting switch and dimmer, the dash, and the stereo, but none of that helped, either.

I feel like I'm close, but maybe I'm completely misunderstanding. Anyone have any ideas?

 

[mark sr]

How old is the battery? it should show close to 13 volts but the only way to know for sure is with a load tester.
Most auto parts stores will test your battery for free if you have a way to get the battery to the store.
Do you have a battery charger?

 

[beepbloopjoop]

How old is the battery?
Do you have a battery charger?

It's a new battery, and I have an old Die Hard battery charger/tester that I use to recharge it if it's lost power to the short.

 

[JPNinPA]

Between the body and the negative battery terminal you measure 12 V or between body and battery + you read 12v?

Battery fully charged should be 12.4V
When starting it should not go below 10v Dip yo 11 at best.

So headlights kill parking lights. This means you need to clean the ground point for the headlights. It is poor and the marker lights are finding ground through the headlights.

In general it is a ground issue and you need to clean all grounds. Battery to chassis and battery to engine.


Never look down on anyone unless you are helping them up - Jesse Jackson

 

[beepbloopjoop]

Between the body and the negative battery terminal you measure 12 V or between body and battery + you read 12v?

Negative lead of the multimeter connected to the negative battery pole, and positive lead of the multimeter connected to the body/alternator/common yields around 12v on the readout. This is why it seems to be a short to the ground, because it seems like maybe a positive short is touching a common ground. Strange that it's only showing 3 fuses with 12v on their (-) side.

So headlights kill parking lights. This means you need to clean the ground point for the headlights. It is poor and the marker lights are finding ground through the headlights.

The headlights and front parking lights are incandescent, while the rear lights are LED. The parking lights don't draw nearly as much as the headlights, so I think maybe the headlights are too much load under the circumstances. I pulled the headlights and that didn't affect the problem.

In general it is a ground issue and you need to clean all grounds. Battery to chassis and battery to engine.

If the problem is that a ground connection is failing, why is the ground (body/engine/etc) registering 12v? It seems like somewhere a positive lead is touching a ground, which is spreading across the vehicle body. Maybe I'm not understanding it correctly.

 

[ndnatty]

If you are measuring correctly and are getting 12v from body to negative battery terminal, then you have a wire that may have rub the insulation off and is making contact with the body. If it is fused, then you would be blowing fuses like crazy. I would think at least.


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[JPNinPA]

That sounds like something is on and the ground to the battery may be bad. Id have to look at the three you mention that are not12v both sides to see if they go through a switch or relay.
If something is on or shorted it would drain your battery. You didn’t mention battery drain.
To check you could take a jumper cable to connect one side to battery ground and the other side of that grounded cable to the chassis or engine and see what is on.

Another thing to try is constantly monitor the voltage across an empty fuse that shows 12v each side. Then start pulling fuses until the voltage changes. It should go from 0 to +/- 12V . This will identify what circuit is shorting.




Never look down on anyone unless you are helping them up - Jesse Jackson

 

[JPNinPA]

Agree with ndnatty on the fuse popping. Anything directly wired to the battery?

Also this is a good read I just found. Fluke is a major mfg of high end electronic equipment including multi meters.
Diagnosing Voltage Drops Electrical Automotive Troubleshooting | Fluke


Never look down on anyone unless you are helping them up - Jesse Jackson

 

[beepbloopjoop]

I figured out the issue and came back to share along with the advice to be careful what you "know" when you're diagnosing issues like this.

I was getting a reading on the ignition fuses because I was trying to diagnose with the key/ignition on.

I was getting 12v on the body because the negative battery cable was unhooked, but the positive was still connected.

I hooked the battery charger back up, positive on the positive clamp which was on the positive battery post, and negative on the body. I realized that while the charger was hooked up, everything worked, so this was more of a dead battery situation but how? The battery was charged and ready... I was going to test the alternator output at the battery both of and running, but when we turned the key there was a loud pop at the battery and nothing worked, again.

The loud pop was on the battery, at the positive clamp. While it looked fine, it was getting such a bad connection that it wasn't working. I replaced the positive clamp with a new lead-free version, and it started and ran without trouble.

Thanks for all the suggestions, here. Much appreciated. I hope I can help some of you out, too.

 

[JPNinPA]

Good job!!!
Great feeling to have fixed it yourself.

Bad batteries snd bad wiring can cause a lot of headaches. Phantom CELs pulsing lights, intermittent problems…
It is usually my first recommendation to check wires and ground connections…
Should inspect every 30 k miles or 3 yrs.

Glad you got it fixed!

Never look down on anyone unless you are helping them up - Jesse Jackson