ALT light stays on faintly

Anyone have this?
Voltage is 14.4 V at the battery when idling, so I think the charging circuit is good.

It didn’t do this before I cleaned everything out and put it all back together.

THe ALT light is bright when I turn the key on, as normal, but after start up you still see it faintly on. No pulsing, just slightly on.


What did you clean out? For the bulb to be lit there has to be a voltage difference across the bulb.

xr7: I pulled all the intruments/dash/AC/heater to clean out and repair what it needed behind the dash board. I didn’t really take any of the driver’s light/guage assembly apart though. I kept it together is one unit, except for installing a tachometer in the fake clock spot.
I guess I’ll have to look at the wiring diagram to investigate the Voltage Difference potential in the circuit. Thanks for that tidbit…

I’d be curious to know if you figure it out. my son’s 69 has the same symptons. he was having charging issues last summer and we ended up replacing the alt, volt reg and starter solenoid. about 2 months after that the alt light started doing the same as yours and has been for the last 4 months. we’ve got good voltage at idle and haven’t had any problems with the battery not being charged but it’s annoying and didn’t do it before.

I am wondering if you might have re installed the wires on the side posts of the solenoid wrong.

The ALT light has power to both sides. Normally one side gets it from the ignition switch or cluster feed (CVR/IVR). The other side is wired to the I post of the voltage regulator by the battery. When there is more voltage in the battery than the alternator is putting out the current flows through the bulb to the regulator through the alternator to ground.
A bad diode in the alternator can cause a dim ALT light, as can a short on the alternator side of the bulb going to ground.

Since all you did was clean the cluster w/o removing any wiring it has to be something else…

You installed a mini tach - Where did you connect power and ground for the tachometer? It could be the regulator side of your light is grounding through the tach. I would disconnect the tach and see if the bulb goes out.

It will take me a while to pull the dash and try some of these troubleshooting ideas. Finishing up the TriY and dual exhaust with FM delta 50s. Just need to attach tailpipe hangers. Sounded good though!

I will definitely write back with what I find.