View Full Version : Battery loses charge

02-22-2008, 12:00 AM
This is for anyone that knows what electrical problems could cause this. I have a 98 and my fairly new battery loses it's charge after a few days if I keep the battery cables connected. One thing that's going on is that I can't set my factory theft deterent system or the alarm will go off in about a minute or so. Also getting out of my car today several times I would get a little shock when I would touch the outside of the door.:eek: I am getting tired of having to manually lock my doors so the alarm doesn't go off. Can't even use the power locks to lock the doors. Maybe there is a short somewhere? Alternator? Relays/modules? Has anyone had a problem similar to this? Any opinions or insight would be greatly appreciated.:thumbsup:


02-25-2008, 11:39 PM
It sounds like there is a "neutral" wire in the PATS (Passive Anti-theft System) that is somehow shorting to chassis ground and thus tripping your alarm, while also raising chassis ground above its ordinary electrical potential.

This might perhaps be caused by a shorted or open relay or electronic component, or by a wire that somehow got smashed and cut and is thus shorting neutral to chassis ground.

The PATS (Passive Anti-theft System) is controlled by the PCM (Power-train Control Module) that is inside the passenger-side kick panel, so it might be that there is a failed component in the PCM, perhaps a filter, or isolation, capacitor that is shorted to ground. This sort of short could be verified electrically by a "black-box" swap: replacing temporarily the suspect PCM with a known good PCM that is compatible with your Cobra. Even so, I would be sure to eliminate all other possibilities in terms of crimped and shorted wires before putting a known good PCM at risk via a black-box swap.

If you are getting shocked by touching metal, there is definitely something fishy about the relationship between "neutral" and "chassis ground": Hot (+5v or +12v) wires that short to ground cause fuses to blow and/or electronic components to smoke. :firedevil

Neutral wire problems, however, usually prove much more difficult to track down.

Best wishes in locating the problem.

cheers, :cheers:

--Professor Chaos

02-26-2008, 08:07 AM
Hopefully I can locate the problem fairly easily. Thanks for the advice!:thumbsup:

RF Cobra
02-26-2008, 12:28 PM
I had a similar problem with one of the Tbirds and it turned out to be the alternator. Instead of charging the battery like it should it was not cycling correctly and had actually starting draining the battery.

Good luck, hope it doesn't take a lot of searching to get to the source of your problem.

02-26-2008, 01:47 PM
I've had someone else tell me to replace the alternator. Autozone tested it and it was fine. I might just replace it anyway since it is the original. Does anyone have a suggestion on what brand alternator to buy?

RF Cobra
02-26-2008, 04:51 PM
That was the problem I had, my alternator tested fine too. Luckily when it happened we were in Florida visiting the in-laws for a couple of weeks. My father-in-law worked for a Lincoln dealership and it took them several times to figure it out. Alternator always tested okay. They finally caught it when they started monitoring the load on the battery and after eliminating the alarm system drain they traced the problem to the alternator discharging the battery when the engine was not running.

Not saying the alternator is your problem, but it did take them several attempts on mine to determine that actually was the problem. Be nice if you could try one out for a couple of days to see if that fixes the problem.

I've always just used Ford reman. alternators.

03-11-2008, 06:58 AM
I have to add my two cents here... The alternator windings when measured by an ohm meter will appear like a low resistance to a short circuit. This is normal. The issue at hand would be the passive devices such as the diodes that prevent current from flowing into the alternator. If the diodes are compromised or damaged, they could leak a fair amount of current into the windings of the alternator causing the battery drain. Bad diodes will also prevent the alternator from charging the battery. Another component that could be at fault is the voltage regulator which is usually connected to the alternator or may be an integral part of the alternator itself. Diodes are usually located in the power distribution box in the engine bay. One sure way to find out what is going on is to test the voltage across the battery when the engine is running. A good system should generate 14vdc. If the voltage begins to drop, it may be due to several thinigs, bad diodes not allowing voltage to pass, worn out contact in the alternator, or a shorted cell in the battery. As for the electrical discharge, that may be considered normal especially when composite materials are used near parts that generate high amounts of electrostatic energy such as the engine bay and even the tires or brake pads... The composit materials act like capacitors that store the high levels of static energy. Once you touch the door or panel you are the one discharging the high potential energy ( voltage in excess of 10kV). If it was based on the 12 volt system, you would not feel the discharge unless you are the shorting conductor for the battery itself which would probably cause serious injury. I get zapped a few times when I drive my 04 ever since I removed the hood liner.

03-11-2008, 11:16 PM
Thanks Ausie!:thumbsup:

05-01-2008, 07:41 PM
Any luck with the battery charge issue?