Ultra Senior Member
Loc: Plano, TX
10-03-16 08:20 AM - Post#2654640
In response to chiefdlf
Typically when the IGN switch is ON with the engine not running, the ALT lamp should light. That's because the lamp has battery voltage on one side and is grounded on the other -- through the white "field" wire connected to the alternator windings. But when the alternator is spinning, there's 13-14 volts on the windings, and on the white wire.
The above is applicable to 10SI and 12SI internally regulated alternators, but I'm not sure if it's the same for external regulation. Which do you have?
1982 C10 SWB pickup: Unmolested base truck, original paint. Originally had 250 six and 3-on-the-tree
Now has 355 with Vortec heads, RamJet roller cam, LS6 beehive springs, TH350
Retired, but working part-time on 50s-70s cars & trucks.
Edited by MikeB on 10-05-16 08:57 AM. Reason for edit: No reason given.