Changed Alternator and Regulator and ALT light still glows

[UKPR1]

Subject line says it all. What could it be? I even tried running a independent ground to the new regulator but without any change. The dash ALT light still glows faintly (like 1/2 power). When the truck is started, it comes on bright and then glows dimmly as long as the truck is running. RPM's have no effect.

Thoughts?

Geoff

[390FE1972]

Here are a few threads that talk about the alternator light staying on:

http://www.fordification.com/forum/view ... =8&t=54556
http://www.fordification.com/forum/view ... =8&t=59765
http://www.fordification.com/forum/view ... =8&t=44122
http://www.fordification.com/forum/view ... =8&t=71737

Hopefully these help!

[UKPR1]

It certainly does. Thank you for this. I'll 1. Try the key trick. 2. Try another regulator. 3. Try another Alternator.

Geoff

[UKPR1]

So the key trick kinda worked. I could turn the key back ever so slightly right before shutting the engine off and the ALT light would turn off. But I got the impression I was "fooling" the switch and it was simply balancing on edge of shutting off. Given my impressions, do you think my switch is still bad? I swapped in another regulator - this time a brand name - and the result was the same...light came on. In looking at the wiring diagram, wire 904 (Grn w/ red stripe) out of the regulator runs directly to the ALT light, and is probably energized when the regulator senses something wrong - voltage either too low or high. So...here's my thoughts on what is most suspect:

1. Not likely bad wiring as light comes on bright and then gets dim. Wiring is intact and has continuity. Bad wiring or a bad ground would make the light not come on at all, right?
2. Mis-wired alternator. I read on one post that an ALT light came on because the wires were on the wrong terminals on the alternator. Have to check this out, but I had some kind of tri-connector on my alternator so I would think that mixing up wires is pretty impossible.
3. Bad regulator. As this is my 3rd regulator (including the original), the likelihood of these continuing to be bad becomes less and less. Although these being the culprit are the most suspect as these sense what's too low or too high and then energizes wire 904.
4. Bad alternator diode. Given the alternator isn't mis-wired, then I have to suspect this. Although how I test for it, I have no idea... Not likely as I replaced the alternator to correct the light-on issue and although my charging volts improved (into the 14's at idle) the light-on issue continued.
5. Bad regulator connector from the alternator or starter relay.

If it's not one of these, then I'm at a loss...

Geoff

[UKPR1]

So in doing the test of pulling off the regulator plug with the key in the on position (not running) shuts the ALT light off, so in doing this, as others have stated, hopefully tells me that the ALT light isn't being backfed some other way - it's definitely completing it's circuit from the regulator. Now the puzzling part: the light gets it's power from the instrument cluster plug and the regulator gives it the ground it needs to light up. Why then, when I test for voltage at the terminal on the regulator that feeds the light, am I getting 4.5volts? Is this where my dim ALT light is coming from? Do I just keep on buying regulators until one works? My local part houses are not accepting returns on electrical items and this is starting to get expensive. What brands are you guys using?
One more "maybe cause" that I'll verify tomorrow: I saw a schematic where are it looked like there were TWO resistor wires that come of the ignition. One goes to the coil and the other back to the regulator by way of the red plug in the engine bay. When I wired in a new ignition pigtail, I'm not sure that I reconnected the regulator resistor thinking it was for the coil (as I went to Duraspark and didn't need the coil resistor wire). I'll verify tomorrow, but for the electrical gurus out there - could this the the cause of my problem?

Thanks in advance,

Geoff

[UKPR1]

Word to the wise, when upgrading the dash cluster bulbs to LED's, leave the Alternator warning light bulb alone (Bulb 1895). It's actually an integral part of the charging circuit and provides a certain amount of resistance that the circuit relies on seeing. What a waste of time and money chasing this one...when it was a $2 bulb...

Geoff

[390FE1972]

Thanks for letting us know what worked for you!

Regards