Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Ford F-150 blinking alternator light electrical problem

This one is driving me crazy. 1978 Ford F150 with lots of miles. When everything is okay, turning the key to the OFF position kills power to the accessories (as it should). If the key is turned to the ACCESSORY position, the alternator light comes on, as does the accessories.

But about half the time, when the engine is turned off (and key to the OFF position), the alternator light flashes dimly. If a radio is on, it stays on, and the accessory fuse positions read about 9 volts. Even if the connector to the back of the ignition switch is removed, nothing changes. The only way to “fix” the problem is to restart the engine several times and try again. Or (as I just discovered) disconnecting the battery and reconnecting it fixes the problem (until the next time the engine is started).

Feels for the wold like a sticking relay, but I can’t find it. Maybe something in the voltage regulator? Anyone have ANY ideas???