Electrical Dead Short

[carterchapman]

Put the XLR away last October for winter. As always, I put a trickle charger on the battery which I remotely activate 1 full day per month. Been doing this for 10 years. Came from our FL home last week and noticed the battery (AGM) was deader than a doornail. It would not take a charge. Before I picked up a new battery, I pulled my battery disconnect and attempted to recharge the battery. It took a full charge. When I put the knife blade disconnect back to the battery, BIG spark, radiator fans came on, and in 5 seconds the neg cable was red hot. Immediately disconnected.

Car ran perfectly when I put it away in October, what the heck could cause this?

 

[nvme]

Put the XLR away last October for winter. As always, I put a trickle charger on the battery which I remotely activate 1 full day per month. Been doing this for 10 years. Came from our FL home last week and noticed the battery (AGM) was deader than a doornail. It would not take a charge. Before I picked up a new battery, I pulled my battery disconnect and attempted to recharge the battery. It took a full charge. When I put the knife blade disconnect back to the battery, BIG spark, radiator fans came on, and in 5 seconds the neg cable was red hot. Immediately disconnected.

Car ran perfectly when I put it away in October, what the heck could cause this?

One thing that could cause that to happened is a dead short. Like putting the hot wire on the negative and the ground wire on the positive?

 

[carterchapman]

One thing that could cause that to happened is a dead short. Like putting the hot wire on the negative and the ground wire on the positive?

That's exactly what it sounded like, BUT my battery cutout is on the negative terminal and the battery terminals are not moved or touched from their original positions...

 

[nvme]

That's exactly what it sounded like, BUT my battery cutout is on the negative terminal and the battery terminals are not moved or touched from their original positions...

Maybe? Since the battery was completely dead and when you hook up the cables to recharge it you put the cables in the opposite direction and since it was dead no sparks when you connected them on your completely dead battery??

 

[nvme]

Maybe? Since the battery was completely dead and when you hook up the cables to recharge it you put the cables in the opposite direction and since it was dead no sparks when you connected them on your completely dead battery??

 

[nvme]

By the way You can test that theory with a volt meter, you might have a battery with a positive ground and not a negative ground. I remember in the old days you had to specify whether it was positive ground or negative ground on the old 6 volt battery..

 

[mickeytee]

You may have varmit damage that has eat a wire causing it short. The fan wire is always hot so if you tyrn the car off hot it would run so id look around the fan control module.also the battery could have dead short inside . id make up a wire withba ten amp fuse to put between the positivevand the battery before installing it

 

[nvme]

By the way You can test that theory with a volt meter, you might have a battery with a positive ground and not a negative ground. I remember in the old days you had to specify whether it was positive ground or negative ground on the old 6 volt battery..

 

[nvme]

What did you find out about the dead short circuit or you haven't you found it yet? Also what is a cutout switch on the negative cable? I have a 2008 xlr and as far as I know mine doesn't have one..

 

[mickeytee]

No car made in the usa has a positve ground. Never seen one on anything else. The cutoff is a disconnect switch that goes on the battery . used to hitrods and boarsvavlot for cars in storage. Just twist and the battery is disconnected without removing the cable

 

[carterchapman]

Battery worked fine last few seasons. Cables were not moved. A Cutout switch allows a battery to be disconnected without removing the terminals. @mickeytee is correct.

 

[carterchapman]

No evidence of rodents - good suggestion, thanks.

Going to pull all high amp fuses and try again...see if I can isolate the grounding circuit.

 

[RubyRod]

One of the things to keep in mind is that while the car is "off" there are lots of electrical circuits that are powered. Things like the RF Remote receiver, the power seats, parts of the ECM & BCM are powered so that when you press the "Start" Button on the Dash the car will start, etc. So while the car may be in the "off" state it is still drawing current from the Battery. This is likely what caused your Battery to fail.

As for the "short" circuit that is causing the Negative Battery Cable to overheat you'll have to search circuit by circuit for this "short". If you have an analog Ammeter connect this in series with the Battery Disconnect Switch. If not you can try a digital meter (DMM) but you'll need to use the unfused 10A circuit so beware of damaging the meter. Best to connect a fuse in series with the DMM if you go this route. After you have an Ammeter connected start removing fuses & relays in the Engine Fuse Box one at a time until you see the current drop in the Ammeter. If you don't find the short in the Engine Bay Fuses you'll have to start with the Fuse Box under the Passenger Side Carpet (BCM location). When you find the right circuit the current through the Ammeter will drop significantly if you're getting enough current draw to heat the Negative Battery Cable. You'll also want to test in short bursts of connecting the Battery Disconnect Switch to avoid overheating/damaging the Negative Battery Cable, etc.

Also, start by disconnecting the higher amperage fuses & relays first. It seems like one of the larger current draw circuits would be where the problem is.

What is puzzling about this situation is that if you're drawing enough current to heat up the Negative Battery Cable I would expect the related fuse to blow. Don't understand why that didn't happen. I can't think of any high current circuit in the car that does NOT have a fuse. Maybe the headlight relay but I'd have to search my wiring diagrams to know for sure.

 

[carterchapman]

Great points. I'm surprised a fuse didn't blow.

Next I will pull all high amp fuses and see what happens. Also need to look at wiring diagrams as well and trace the positive cable and see if it has a dead short. I did not feel it, but if the negative got really hot in two seconds, I bet it was hot as well.

 

[nvme]

That seems like a lot of pulling fuses in the engine and passenger box. Even if you did find one fuse that is not blown that is just the beginning of the problems that comes your way. Suggestion:: go to the internet to find a positive ground. You will fine that all Fords cars and trucks and trackers were made with positive ground from 1928 Model A to 1955. There some other cars both domestic and foreign such as MG,Triumph but not Chevrolet. The charger doesn't care which positive or negative terminal is connected, the polarity doesn't matter. I'm old guy and I take too much for granted so I could hook up the charger with reverse polarity, very easy for me. Check it out with a volt meter or buy a battery from a auto parts store, they will help you to install it and fore warn them about the problem. Good luck, let me know.

 

[carterchapman]

Thanks. I just haven't had time to check anything yet - summer boating season takes all my spare time. I'm going to get my VOM out tomorrow and see what it shows.

 

[carterchapman]

One of the things to keep in mind is that while the car is "off" there are lots of electrical circuits that are powered. Things like the RF Remote receiver, the power seats, parts of the ECM & BCM are powered so that when you press the "Start" Button on the Dash the car will start, etc. So while the car may be in the "off" state it is still drawing current from the Battery. This is likely what caused your Battery to fail.

As for the "short" circuit that is causing the Negative Battery Cable to overheat you'll have to search circuit by circuit for this "short". If you have an analog Ammeter connect this in series with the Battery Disconnect Switch. If not you can try a digital meter (DMM) but you'll need to use the unfused 10A circuit so beware of damaging the meter. Best to connect a fuse in series with the DMM if you go this route. After you have an Ammeter connected start removing fuses & relays in the Engine Fuse Box one at a time until you see the current drop in the Ammeter. If you don't find the short in the Engine Bay Fuses you'll have to start with the Fuse Box under the Passenger Side Carpet (BCM location). When you find the right circuit the current through the Ammeter will drop significantly if you're getting enough current draw to heat the Negative Battery Cable. You'll also want to test in short bursts of connecting the Battery Disconnect Switch to avoid overheating/damaging the Negative Battery Cable, etc.

Also, start by disconnecting the higher amperage fuses & relays first. It seems like one of the larger current draw circuits would be where the problem is.

What is puzzling about this situation is that if you're drawing enough current to heat up the Negative Battery Cable I would expect the related fuse to blow. Don't understand why that didn't happen. I can't think of any high current circuit in the car that does NOT have a fuse. Maybe the headlight relay but I'd have to search my wiring diagrams to know for sure.

I've got the two shop manuals (Vol 1 and 2), but they don't have wiring diagrams - that was a surprise!

All I can figure out is maybe the positive cable has a short directly to ground. So I need to figure out where its first junction is and check the cable...

 

[mickeytee]

Unlike what some people claim, the two volumn sets do not have the same information as the 4 and 5 volumn sets.

 

[carterchapman]

I did not know that! Thanks Mickey!

 

[MPRCTCL]

Unlike what some people claim, the two volumn sets do not have the same information as the 4 and 5 volumn sets.

... and the PDF versions have even less