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Alternator charging problem

1K views 16 replies 10 participants last post by  cerial 
I'm pretty sure the cable you have circled in red on your picture is the power wire going to the fuse box in the cab.

The alternator charge cable usually runs back to the starter. And if there's a fusible link, it's generally at the starter end.

Start checking voltages at the battery and at the starter power post (where the battery cable is attached) with the engine running. It should be close to or over 14V the whole way.
 
If your alternator is an exact replacement for the stock alternator (exact same amperage capacity), making an exact replacement for that would work.

Do both wires go to the same place? If they do, you might be better off upgrading to a Midi fuse bolt down fuse block and fuse on the firewall, next to the junction that the wire goes to, with a single larger wire connecting that to the alternator, and a short larger wire connecting that to the alternator. Fusible links are a PITA, even for someone who does soldered lap or lash splices all the time.

Two cables in parallel = "-4" on the AWG size of the wire. So if that's 2 12AWG wires, it's equal to a single 8AWG wire. And if you absolutely must use a fusible link, you want fusible link wire (it's a special kind of wire) that's 4 gauge sizes smaller (+4 on the AWG number) than the wire it's protecting, and there should be at least a 4 inch +- piece of the fusible link wire in the circuit.

If you've upgraded the alternator to a higher capacity, higher amperage unit, you need to upgrade that wire to a larger size. The size of the wire depends on the amperage capacity of the alternator.
 
One thing I find helpful when chasing a "dead short" is a light socket with bulb, with alligator clips on the wires. Disconnect the negative battery cable and clip the light between the battery post and the cable end.

The light bulb will limit current/power to the wattage of the bulb, and it will be bright if there's a dead short. If there's very little current draw, the light will not illuminate, and it will allow low current to pass through with little resistance. This is also helpful (with a lower wattage bulb and matching socket) for chasing current drain issues.
 
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