Another parasitic battery drain story...
#1
05-26-2015, 08:46 PM
Another parasitic battery drain story...
I was feeling pretty smug about getting my 92 F150 XL ticking like a Swiss watch, when my wife asked to borrow it. It hadn't been driven for a few days, but sure, no problem.
About 2 minutes later, she was back and said "Sorry, dead battery". She took her Prius and left me wondering. Sure enough, the battery was flat as a pancake--it read a remarkable 0.2 volts--and it was only about 4 months old.
I pulled the negative cable and put a charger on the battery and had no problem getting it to take a pretty good charge. Putting an ammeter between the negaive terminal and battery showed that the truck with the ignition off was drawing about 3 amps--that would do a battery in after a few days. With a newly charged battery, no lights were on, the alternator stayed cold; I couldn't smell anything burning.
I had visions of pulling the alternator or something equally as entertaining. But I thought to do some checks first, and inserted a 12V trouble light between the battery and the negative cable. It lit up, naturally.
Nothing improved the situation until I twisted the **** on the headlight switch--and the trouble light went out. Fiddling a little more with the **** (pushed in so the headlights were off), I found that I could get the trouble light to turn on or off--meaning I'd found the source of the drain. But the headlight switch with the **** pushed full in?
I pulled the instrument panel and looked at the switch--it was sitting in a pile of green dust, with the wire on the instrument lighting rheostat hanging loose. Well, there it was--when the **** was turned in such a way that the danging winding contacted the chassis, it would drain the battery. Replacing the headlight switch got rid of the problem. Oddly, there was enough of the winding intact that instrument lighting worked.
I got lucky--I had visions of pulling fuses and looking for frayed wires. Instead the solution was simple. On the new control, I put some dielectric grease on the windings in the hope that it would retard corrosion somewhat.
So the old beast is back in business.
About 2 minutes later, she was back and said "Sorry, dead battery". She took her Prius and left me wondering. Sure enough, the battery was flat as a pancake--it read a remarkable 0.2 volts--and it was only about 4 months old.
I pulled the negative cable and put a charger on the battery and had no problem getting it to take a pretty good charge. Putting an ammeter between the negaive terminal and battery showed that the truck with the ignition off was drawing about 3 amps--that would do a battery in after a few days. With a newly charged battery, no lights were on, the alternator stayed cold; I couldn't smell anything burning.
I had visions of pulling the alternator or something equally as entertaining. But I thought to do some checks first, and inserted a 12V trouble light between the battery and the negative cable. It lit up, naturally.
Nothing improved the situation until I twisted the **** on the headlight switch--and the trouble light went out. Fiddling a little more with the **** (pushed in so the headlights were off), I found that I could get the trouble light to turn on or off--meaning I'd found the source of the drain. But the headlight switch with the **** pushed full in?
I pulled the instrument panel and looked at the switch--it was sitting in a pile of green dust, with the wire on the instrument lighting rheostat hanging loose. Well, there it was--when the **** was turned in such a way that the danging winding contacted the chassis, it would drain the battery. Replacing the headlight switch got rid of the problem. Oddly, there was enough of the winding intact that instrument lighting worked.
I got lucky--I had visions of pulling fuses and looking for frayed wires. Instead the solution was simple. On the new control, I put some dielectric grease on the windings in the hope that it would retard corrosion somewhat.
So the old beast is back in business.