I'm currently experiencing a short to ground on my 97 F150. I have reviewed other previous posts on the site concerning shorts and followed suggestions on finding where the problem lies. Under the dash, I have taken out every fuse one at a time and still measure 12 volts between the battery ground and the ground cable. I have also performed this test with all fuses and breakers under the hood ( about 30 or more fuses and breakers) but never breaking the voltage to the ground cable. Are there any fuses or breakers located somewhere I might be missing? ( The ones under the hood are under the covers on the drivers side). I'm lost except to take it to an automotive electrical professional. Any suggestions or help is appreciated.

Thanks,
Dan Benson

 

Why do you suspect you have a short to ground? Unless you added circuits that are not fused the fuse protecting that circuit would blow. Just check the circuit with the blown fuse for the short.

JMC

 

I know I have a short to ground because if I don't drive the truck for 2 days the battery will completely discharge. No fuse is blown. If I take the ground cable off the battery I read 12 volts between the cable and the negative post of the battery. I've had the charging system checked and all is ok. Also, removing the negative battery cable will not discharge the battery. Should be no voltage there (ground to ground). It will also burn a 12 volt light ( not bright, weak light) between the neg cable and the neg post of the battery. I have added no circuits, everything is what Ford made. I thought everything would be fused but somewhere i'm missing a fuse or it's feeding back un-fused.

Thanks,
Dan Benson

 

i would suspect an electrical device before a wire harness. the starter relay and maybe the starter. test the voltage drop like you are doing and then start unplugging and disconnecting things
its not really a short but just a draw through something.

my first guess would be the starter relay (or any other relay) is arced across the contacts and drawing a little current.

 

Thanks for the suggestion, I didn't think about relays. I'll start with the starter relay and go from there. That sounds more like what is happening.

Thanks,
Dan Benson

 

Glovebox and underhood lights are well known for doing this.

Remove both bulbs and see if the draw goes away.

Steve

 

There should be no more than a 0.05 amp draw when everything is turned off. Did your test of the charging system include the battery?

JMC

 

There will most likely be a 12V potential between the negative cable and the negative post when disconnected. That would be normal.

The thing to look at, as JMC mentioned, is the CURRENT between the cable and post. That'll give you a better idea if anything is wrong.

There are MANY things that will continue to draw a slight bit of current even with every fuse out. The GEM module, PATS system, stereo memory, and RKE receiver all come to mind, and I'm sure there are others.

-Joe

 

To test this current dray you have to run a jumper wire between the NEG battery terminal and the battery post. Run the engine for a few minutes and shut it off. Wait about 40 minutes for the battery saver to power down and then connect an ohm meter between the terminal and the post and disconnect the jumper wire. If at any time you open the circuit you will have to start over again. If the draw if over the 0.05 ohms start pulling fuses till you get to the circuit that lowers the draw.

JMC

 

I appreciate all the suggestions. I will try removing the hood and glove box lights first and check results. I will then try the current test. I will post my results when I find the problem. Again I appreciate everyone on this site. I have saved myself much time and money from the expertise here.
Sincerely,
Dan Benson

 

That is a correct measurement. You are measuring battery voltage through whatever devices are still connected and your meter is completing the circuit.
You need to measure the current flowing between those points. If everything is off you should be able to do that with an ampmeter or the amp setting on your multimeter. Be sure to move the probes to the correct sockets (usually clearly marked with an A) on your meter or you could damage it.

 

When using that method (measuring voltage or amps), or using a test light, you have to make sure all other loads are turned off. For example, if your door is open, and the interior lamps are on, your results will be flawed. Make sure you have your doors closed, the underhood lamp unplugged, etc., when you test for your mysterious draw.

 

I have the same problem ('97 F150, 4.2L). The battery will die after a few days.

I removed the negative cable and measured current from the cable to the battery post without any electrical stuff on. There was about .15A. Too much.

So, I started pulling fuses. I pulled a 15A fuse ( I think it was # 14 or 15) and the draw was only .03A, right where it should be.

The fuse in question protects the interior lights and the accessory delay relay.

Now I am stuck. What is this relay and could it be the problem? Other than that, failed insulation on any of the light circuits?

I sprayed WD-40 into the door latches, but am otherwise out of ideas. Thanks

 

Did you wait the requisite 30-45 minutes for the battery saver relay to timeout (or remove the relay) before testing?

Steve

 

No, I didn't know about the battery saver relay. I will find it and pull it for the next test. As well, I am going to check the glovebox and underhood lights.

Any idea what this accessory delay relay does and whether it could be part of the problem since it is on that circuit?---Jack.