Strange Electrical Problem

[biglar]

This is a new one on me - if I leave my 2002 SR5/3.4 sit for a couple of days, it'll suck the battery dead. New battery about 3 months ago.

There are 2 cables coming off the positive terminal - one goes directly into the fuse box; the other goes down under front of engine and another comes back to the fuse box.

I tried un-hooking them 1 at a time and leaving it sit overnight, then put a digital voltmeter on it. Full charge - and I do check - is 12.6 volts. If I dis-connect the one that goes directly to fuse panel, voltage will be below 12 next morning.

If I dis-connect the one that goes under engine, voltage will be ~12.3 or 12.4 and will stay there for days.

OK, something is drawing power thru that under engine cable, right ?? A bit ago I went out there with my little portable ammeter in hand, puilled each fuse one at a time with both cables hooked up and went thru all of them. None show any power draw.

OK, again - I dis-connected that "bad" cable and connected the ammeter between it and the positive terminal.......and it shows no draw. NWTH ??:wtf:

 

[JSwain]

Full charge of a battery should be 12.8-13.0V. Your 12.6 is actually about 50% capacity which leads me to believe your alternator isn't charging to its potential, or your battery has been drained too many times to take a full charge. You mentioned it's a newer battery...what about the alternator? When your truck is running and you test V at the battery do you get 13.8-14.4V?? If it does I would bring your truck in to a parts store and have them load test the battery for you. And btw they should test it free for you, most of them will test the Alt for free too if you tell them you will replace the bad part through them, whether or not you put it in yourself. Hope this helps

 

[Buckaroo]

Across the battery terminals, 12.6 v is a fully charged battery with the engine off. With the engine (and alternator) running, it should be ~13.5 - 14.5v across the battery terminals.

I think you are looking for a parasitic draw. One way to approach it....with the car off and all the electrical loads turned off, unhook positive cable and put a test light in between terminal and cable. It should not light. If it does, let it sit for ~30 minutes (to make sure that the computer has gone to sleep). If it continues to light, start pulling (& then replacing) fuses one by one. When you get to the circuit that has the issue, the test light will go out. Then you can trouble shoot the items on that circuit.

good luck

 

[Skidmarcx]

Agree with the above... And to be exact 12.66v is fully charged

 

[Forrrrest]

Across the battery terminals, 12.6 v is a fully charged battery with the engine off. With the engine (and alternator) running, it should be ~13.5 - 14.5v across the battery terminals.

I think you are looking for a parasitic draw. One way to approach it....with the car off and all the electrical loads turned off, unhook positive cable and put a test light in between terminal and cable. It should not light. If it does, let it sit for ~30 minutes (to make sure that the computer has gone to sleep). If it continues to light, start pulling (& then replacing) fuses one by one. When you get to the circuit that has the issue, the test light will go out. Then you can trouble shoot the items on that circuit.

good luck

Nail on the head. Or you can hook up an inductive ampere probe over all the wires on the positive terminal. Any. Current draw above .05 amps is considered a parasitic drain. the start pulling fuses and cheap the meter after every fuse you pull.

 

[biglar]

Nail on the head. Or you can hook up an inductive ampere probe over all the wires on the positive terminal. Any. Current draw above .05 amps is considered a parasitic drain. the start pulling fuses and cheap the meter after every fuse you pull.

Thanks for the responses. Parasitic draw is my thought, too. But.......

I have the same voltages after stabilization in my camper, so not too worried about the charging. Incidentally, I don't drive it enuf to charge up the battery (I ride a motorcycle most places) but I did use a smart charger to bring it up.

I used a slightly different way to test circuits - I'm not familiar with the test light between terminal and cable. I don't own a DC clamp-on ammeter but I do have an in-line ammeter that reads up to 10 DC amps and I've crimped small male ends on it to plug into. With ignition off, I pulled fuses one at a time and connected the ammeter between female sockets. It showed nothing on all terminals, yet the battery still holds a charge with one main battery cable disconnected but not with the other.

Thinking on that, I think I'd best try that little ammeter on a known live circuit, tho' it has worked fine in the camper so far. In the dark last night, I touched the power draining cable briefly to the terminal and it did show light sparking, indicating a power draw

 

[biglar]

Quick up-date - you're not going to believe this. For years I've had a Lowrance i600C GPS unit in my Runner and left the power cord plugged into the hot-all-the-time power outlet. Never a problem.

Recently I bought a motorcycle and the Lowrance is too bulky and heavy so I bought a Garmin Nuvi 2555. About the same size screen but thinner and "much" lighter.

The other day I got to just looking at the whole rig and trying to figure what could be different. Only thing was the power supply to the Nuvi........so I unplugged it.

End of problem - battery stays charged. Who would ever a thunk it ??

Thanks all for the replies................Lar.