I have a 98 C1500 that's been showing voltages around 10v while running. Two batteries were installed when i got the truck and i replaced both batteries and cleaned and checked all grounds the batteries were attached to about a week ago. It ran at around 14v before I replaced the batteries and for a few days after the batteries were replaced. In the last few days its been showing around 12-13v while running and was at around 10v when I drove home from school today, by the time I got home the radio was fading and turning on and off. I hooked a multimeter to the battery once I got it home and it showed 11.8-12.2v while it was off. It starts up just fine and the belt is tight and looks fairly new. What could this be?
Big Voltage Drop
- Thread starter Mattj96
- Start date
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90halfton
I'm Awesome
What rich said
Okay so I had to drive it back to school, when I started driving gauge read around 12v but by the time I was in the parking lot it was bottomed out and hesitating really bad. Went back out just now and it starts fine and gauge reads 12v again! Tested battery terminals while it was idling and main battery was reading about 11.5v but aux battery was reading just under 14v! Also, the speedo was freaking out every time I activated the turn signal. Going to try to like it to AutoZone when classes are out and get the alternator tested.
90halfton
I'm Awesome
It's either a bad alternator, bad battery (or 2), bad connection, or bad wire. It's not a super complicated system. What all are you powering electrical wise? As in subs and/or amp. Electric fans? And check and see what size wire is going from your alternator to the distribution block, and then to your batteries. Is your truck a diesel? If not I suspect someone installed an additional battery as a band aid for a bigger problem.
I'm running a stereo but the speakers are all stock size and no subs/amps. No other accessories that would be drawing like that though. The aux battery was reading 12.6v so i swapped the aux and primary battery in the parking lot and it ran flawlessly the whole way home. Idles around 12v and jumps to right under 14v on the gauge when i get the rpms up, so looks like the alt is working. Both batteries were bought last week and not the 80$ crap ones. I'm starting to suspect there was a ground or battery connection that i missed last week when i checked it. Either that, or i got a dud battery. I have a gas 5.7, and the aux battery has a few fuses (or relays?) attached to the positive terminal, positive terminal attached to the alternator, and the aux negative is attached to the block. The main battery positive is attached to the power dist system and the alternator, negative is grounded on the body, shared with the ground for the headlights. Could i rewire the batteries in series? Probably worth running new wires for the batteries and I'd like to make it as simple for myself as possible.
90halfton
I'm Awesome
If you wire them in series that will make 24 volts. PLEASE DON'T DO THAT! It should charge the same at idle as it does when revved up. Makes me suspect the alternator is on the way out. You should only need one battery. If you want two it won't hurt but for the sake of troubleshooting I would run one (a good one) to narrow down the problem easier. See what size of wire connects your battery to alternator/ distribution block. Small wire makes for voltage drop.
90halfton
I'm Awesome
And also feel around on said wire for weak spots. Had this same problem.years ago and found a spot in the wire connecting the battery to the distribution block where it had gotten hot and was really soft. I think k it was a #8 wire. Replaced it all with #4.
east302
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While you’re at it, check the drop from alternator to each battery. With truck running, compare voltage from alternator post to ground with the voltage at the battery.
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