Updated 1987 suburban not charging?

Question

The battery and alternator are brand new. we tested the wires at the back of the alternator with a light and they both lite up when the truck was running, but the battery was only at 12.5 with the truck running so its not charging. The mechanic thinks the starter is "drawing" electricity and I think the fusible links by the starter are bad.

Answer 1

Put your test light between the battery positive, and alternator charge wire.
It should NOT light up.

If it does NOT light up, turn the engine off.
Disconnect the negative battery terminal.
Now, test continuity between the alternator output wire, and battery POSITIVE.
You should have continuity.

If after all this, nothing is working, go buy another alternator.

I seriously doubt your starter is still drawing power after you start it.

Does you mechanic have an inductive amp meter?

Answer 2

Try this.... with the truck running, disconnect the positive battery terminal, if the truck keeps running the alternator is good and is charging. If it dies then the alternator is bad. I highly doubt the starter is causing any problems.