Only 1 battery functioning?!?

[timothyr1014]

I know the truck WANTS new batteries, and for some stupid reason (probably cuz its not a fun and rewarding project) I have been putting it off...I left Phoenix at 2AM for california (started no problem at 54*), and stopped in quartzite for gas...34* and VERY slow cranking (guess the battery project could have been rewarding). No one was around to jump me, and the "electrician" side of me said swap the batteries side to side (the battery furthest from the load should technically be healthier)....it came to life (slowly, but at 3:30 in the middle of the dessert slow is better than nothing).

Then I was about 100 miles from home and the headlight switch started freaking...run a jumper direct from the drivers side batt to the headlamp (dangerous I know...but it is now 10PM, I am 100 miles from hoome, and 50 miles from civilization)...worked well (didnt catch fire) and got her home. Went to disconnect the batteries and pulled the passanger side first...lights went off (odd because they are powered by a wire wedged between the terminal and cable of the other battery)....the battery shows 12.1v, however with just the secondary battery connected I have no power in the cab....I am thinking battery cables, but am hoping someone will chime in with am "oh, I've seen that before"

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[timothyr1014]

okay...now I am confused to high hell and am hoping for some advice before I rip everything apart and do it "my way"

both batteries test out fine (12.4 & 12.7 no load)....with both batteries in the loop I get good readings from either one going from the pos battery post to the engine....pull either battery totally out of the loop and all still tests good....connect the drivers side battery by itself and test power at the pass side cables (which are not connected to anything)...get 10.2v; test pass side positive and motor and get 12.4, resistance test pass side neg cable and get .1....what am I missing.....a 2.2v drop accross a 5 ft 2/0 run with no load is freaking huge, and yet I cant find the resistance point.

 

[CDX825]

What year is your truck?

There is a yellow 10 gauge wire with a disconnect that causes no power in the cab. Not sure if this is the same in the 90s model trucks though. The connector usually get corroded and some times melts down.

You may want to look into the head light relay mod to. Takes the load off of the head light switch and makes the lights brighter.

 

[timothyr1014]

Truck is an 86, & I have power as long as the pass battery is connected...if I only have the driv in the loop I have nothing (which in a paralel connection makes no sense to me...headlight mod switch and everything are hapening today as well, just in the debate of rewire everything.

 

[CDX825]

Forgot to mention that yellow wire is on the passenger side fender well. The disconnect failing is a common problem.

 

[ericboutin]

Forgot to mention that yellow wire is on the passenger side fender well. The disconnect failing is a common problem.

Not wanting to hijack...but it has me curious which years this "disconnect" is on....and what was the logic or purpose for it?

 

[vegas39]

Truck is an 86, & I have power as long as the pass battery is connected...if I only have the driv in the loop I have nothing (which in a paralel connection makes no sense to me...headlight mod switch and everything are hapening today as well, just in the debate of rewire everything.

Something in the driver side battery has to be screwed up internally.
I have had batteries do wierd things in the past.
Replace them first and then take it from there.

 

[CDX825]

Its on the 83-86 trucks I know for sure. Its not hard to spot if its on your truck its a fairly large disconnect that has a yellow wire running through it on the passenger side engine compartment. I'm not sure of it purpose other than to possibly make the assembly of the wiring harness easier during production.

 

[timothyr1014]

vegas...thanks...going to pick up some batts now, I was kind of hoping someone would say that because that was what I was thinking, it just defies logic in my mind

 

[vegas39]

vegas...thanks...going to pick up some batts now, I was kind of hoping someone would say that because that was what I was thinking, it just defies logic in my mind

I hope that works for you.
My wife had a dead battery several years back, when I jumped it, all was well as long as I left the jumper cables on. As soon as I took them off, the car stayed running but the radio display was going crazy and a bunch of other wierd stuff was happening. Turns out the battery was shorted somehow internally.

 

[vegas39]

Something else. You might want to check the positive wire that runs from the driver side battery over to the pass side battery. Also check the ground that goes down to the block.

 

[timothyr1014]

ran resistance tests on both wires and they came back good....that was what confused me

 

[opusd2]

I've had issues with the disconnect coming apart when driving, no power to the fuel stop and the truck shuts down.

 

[opusd2]

Which is why I am considering putting a manual fuel stop on the machine.

 

[Goofyexponent]

The battery in my 1/2 ton went kind of werid too. A voltage test showed 11.9 volts. Low, but it should have started the truck. All my lights would light up, and everything else electrical worked fine....but there was no depth to the charge...No amps to make my started whirl over

I agree with changing the batteries out. Why not go with deep cycle batteries? I know next time I buy them for my truck I am putting a set of serious deep cycle batteries in there...just because of the extreme cold I have sometimes.