Mustang Owners Club Australia Forum

Technical & General Discussion Area => Tech Torque Pre 1973 => Topic started by: jiffy on October 21, 2021, 10:20:15 am

Title: ALT light stays on weakly after running
Post by: jiffy on October 21, 2021, 10:20:15 am

So - here's a challenge!!

If you check out the members cars section you'll see that this car has just started for the first time in a gazillion years, and all these parts are new to each other.
I had the alternator rebuilt, and it's good - measures 14v when running. The car has a tach-dash so doesn't have an Alt gauge, it has an Alt Light and an Oil light.

The regulator is a brand new aftermarket item but it's not solid state, it's mechanical as the original ones were.

I turn on the ignition, and the alt and oil light come on brightly. Then I start the car, and it runs and charges, and the oil and alt light go off.
When I turn off the ignition, the engine stops and the ALT light still glows dimly - if I turn on the key the oil light comes on and the ALT light continues to glow dimly, and starting and stopping the engine makes little difference - the ALT light goes off with the engine running, glows dimly when it's off.

If I then disconnect the battery, the ALT light goes off, and if I reconnect the battery the ALT light stays off which is the correct appearance, so it suggests to me that there's some issue with the regulator. Anyone know how these things work??

Thanks in advance

Title: Re: ALT light stays on weakly after running
Post by: peter9231 on October 21, 2021, 01:40:22 pm

Check all you earths
Body earth from battery, not just battery to engine.
Alternator earth
Regulator earth
Alt globe earth
You have a earth differential somewhere in the system.
Peter.