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Old 12-05-2005, 01:46 AM
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79 chevy truck Dead battery.

Im having some problems with my electrical system on my 79 1/2 ton 4wheel drive pickup. Whenever it sits for a few days the battery drains itself. 1st question is there a simple way to isolate and look for the problem? 2ndly If there isnt a a short what else could it be? A friend of mine mentioned the ground straps, Now this basically was my first complete tear down and rebuild project and i didnt pay too much attention to how many and or the location of the ground straps. The only 2 that im for sure about is the the Main ground that connects to the alternator bracket and there is a strap that connects the block/head to the firewall. Thanks in advance for any and all help.

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Old 12-05-2005, 03:25 AM
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Doc here,

Load test the battery, and clean or replace the cables, and check for loose connections at the terminals.

First, to maybe shorten your troubleshoot, this is a very common problem when the diode packs go south in the Alternator. The Didoes when going out, will place a small reverse bias , (leak) in the non~conducting direction and place a drain on the battery just while sitting. The alternator will still charge somewhat though, but is not good for the system semi conductors.

An easy test, is Disconnect and Charge the battery up, 6 to 10 hours at 10 amps, When done, disconnect the alternator, Reconnect the battery. Let it sit an equal amount of time (overnight, 1 to 2 days, whatever..) and then when you return, If it's full charge, that's your prime suspect..Either have it tested replace it outright, or rebuild it ..

Check those other sources of drain..(Glovebox lamps, hood lamps , Vanity mirror lamps, Stuck power antennas, Audio amps wired incorrectly and on all the time..etc..) If after eliminating that, you can't find the source, Check the draw at the battery while sitting off.

Pull the battery cable, get a DVOM, and set it for A X 10, or autorange, or it's highest setting..put the probes between the cable and the battery post and note the readings..in a modern, computerized vehicle with CD/RADIO and memory presets, and clock, it will read between 0.03 and 0.08. If higher, you have a branch circuit drain. (Or bad diodes)

Monitor the meter, and pull ALL the fuses one at a time, until the meter drops...While doing this test remove the fuse or bulbs from dome or courtesy lamps, or you'll get a false reading. When the meter drops, (if at all) follow that circuit and find the source of the draw, Repair or remove it.

If the draw is not to be found at the fusebox, then the diodes are probably the culprit...Again, Disconnect the alternator, and read the drain, It should be normal..If so replace it or repair it.


Set your ground up in this manner, (something else to do while charging the battery)

Run a properly gauged Ground cable from the battery to any handy bolt at or near the starter, From that same bolt get a Battery cable at the parts store, that has two 3/8 ring terminals on each end and attach it there and to the Frame.

Next get some 10 gauge wire and ring terminals and run that from your bolt on the block to the Firewall, and another to the Alternator bracket or mount bolt.

If the Bracket and alternator is powder white remove them both and their hardware, sand or pressure wash them until clean semi shiny metal, dry and reinstall.

You have electrolysis there..and it will also eat a water pump impeller up faster than any acid..The Alternator Bracket and Alternator housing is Aluminum and the block is Steel..(what were they thinking?)

When you go to reinstall the brackets, go to the hardware store and get some aluminum wire compound, and coat everywhere the mount hardware meets steel (bolts, mount surfaces Ect..)

Next get some Wire Braid, (Radio Shack) and install braid from the radiator support to the frame, Fenderwells to frame , hood to firewall, Doors to door posts, gas flap to body, tailgate / Trunk to body.

At each point the wire is grounded, Burnish ALL the paint and grease off to bare metal. Use a proper star-washer and lock. Use sheetmetal or Tech screws where no screws are available.

It sounds like a lot of work, but after you assemble all the parts, it's only a few hours to do..and you'll end up with a system that will work reliably for many years to come..and can eliminate that from your troubleshooting list.

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