No alt light when key is on

kknip · Post by **kknip** » Thu Sep 21, 2006 6:27 pm

I have got all the wiring hooked up in my truck.When I turn the key to ON, the oil light comes on but the alt light does not.I have the cluster out and sitting on the dash.I checked power at the bulb and had power at center pin and ground.I don't have a clue as to what's feeding back through.Maybe the alt is shorted out?

68F250 · Post by **68F250** » Thu Sep 21, 2006 9:58 pm

That would be normal IF the engine was running and everything working properly, power is on both sides of the bulb to turn it off.

But since yours has power on both sides with the engine off, I would suspect the field relay is stuck on in the voltage regulator.

To see if it's the regulator or alternator, check for voltage on the "S" terminal of the regulator with the engine off. If there's no voltage then it's the regulator and if there's voltage then it's a shorted diode in the alternator.

kknip · Post by **kknip** » Fri Sep 29, 2006 6:13 am

Thanks a million 68F250!

I thought there could be something wrong with the regulator,but I did not want to just start replacing parts.I did not know the bulb would have power on both sides to turn it off and thought I had something feeding back...........

I love FORDification

68F250 · Post by **68F250** » Fri Sep 29, 2006 11:22 am

You're welcome! The last time I experenced the alt. light not coming on, I had a shorted diode in the alternator. And that was soon after I gave somebody a jump, an expensive jump.

fordman · Post by **fordman** » Fri Sep 29, 2006 11:48 am

one thing i have heard is that you dont arc your cables together to see if the first battery has good connection to the cables because it could burn out the diodes in the alt. thats only what i heard.

68F250 · Post by **68F250** » Fri Sep 29, 2006 11:54 am

You can blow up a battery that way too!

I don't even have my engine running when I give a jump now. The initial surge can shock the alternator as it tries to keep up.