Battery Not Keeping Charge.... Is it my coil?

[brandon]

I got a 1979 Chevy C-30 Dually. Within the past year i have put in a new battery,alternator, and starter. When i charge the battery overnight the gauge reads 13 or a little below. After a few days it seems the battery is losing its charge. Eventually it will go down to 8 volts and the gauge lights get so dim in the dark it's hard to read the speedometer. I asked a couple of guys at work and was told this could be my coil causing it. Any suggestions? I would really like to get this fixed right, the first time, that's why i came here...

[jaredts]

I may be wrong but it sounds like wiring.  Take your battery terminal clamps off the cables and see if the cables are corroded there.  Check to make sure the ground wires are in good condition.  If in doubt run a couple of extra ground wires--they are cheap, easy insurance.  I had the same problem recently and the above procedure fixed it for me.  At a minimum you should have a ground cable from the battery to the alternator bracket, a ground from the battery to the fender or core support, and a ground from the engine to the firewall.  If you don't at least have those you should add some extra ground wires.  I think my problem was the negative battery terminal clamp.  It looked perfect but when I removed it from the cable there was a lot of corrosion in there.  If you have low voltage with a new alternator and the engine running--it is almost certainly this.  Otherwise your new alternator is a dud (easy check with a multimeter at the alternator).

[brandon]

Thanks for the reply, I'm almost positive that i have the ground wires going to the alternator bracket and the fender. The engine i'm not sure of. I can check the terminal clamps, that would be a pretty cheap fix... Its seems as though it has just started doing this lately. I never noticed it before. Maybe one of them is loose...

Now my time to be the newbie... How would i check the alternator voltage with a multimeter, is this the same as an ohm meter? I have a meter with red and black pin tips.

How do i check it, and what reading should i get?

My grandfather was an alcoholic lineman for the local electric company, and when my mother was 12 he "accidentally" grabbed a hold of a live wire,shot holes of electricity through his boots, and died. He used to throw up high-rise towers in NY, he knew what he was doing. I don't want to follow in his footsteps but would like to know how to use his tools.

[VileZambonie]

Use a dc volt meter. put it across the battery terminals. B+ and B- in your V and com port. Use the 20V dc scale if it's not auto ranging. run the engine at 2000rpm with the headlights on and the heater blower on hi. report your voltage reading.