Alternator light stays on despite no keys in ignition.
 

Hi,
I have a technical question. I purchased Superformance SPO3417 as a roller in February of 2021. We are now installing the drivetrain and have come up with a problem. When we hook up the battery, the alternator light comes on and stays on despite no keys in the ignition. We had the alternator and its diode tested at a local alternator shop and it checked out fine. We found that the blue wire is hot at the voyage regulator all the time. Any suggestions as to what our next step should be would be greatly appreciated.

Thanks,
Dan Hartz

The "classic" voltage regulator has four connections to it: I, A, S and F. The charging light is wired between the I terminal and the ignition switch. When the ignition switch is turned on (but the car is not running), the light receives 12v+ from the ignition switch and the path to ground is through the I terminal on the voltage regulator. When the engine is running, and the car is charging properly, the I terminal is no longer a path to ground and becomes energized itself -- so the light goes out. On very rare occasions, the positive output from the I terminal, when the engine is running, can be so high as to light the bulb, but you can forget that for now and instead figure out from which side of the bulb the 12v+ is coming from when the ignition switch is off.

Pull the connector off the bulb and put a VOM lead on each side of the plug, with the ignition switch off, and tell us which side of the plug is getting 12V+. Is it coming from the "ignition switch" side or is it coming from the "voltage regulator" side. Once you know that, you can then explore as to why the circuit is wired up incorrectly. At first blush, I would say the bulb's lead to the ignition switch is on the wrong terminal of the switch and is getting power all the time instead of being switched. But we have to check, we can't just guess.:cool:

Thanks for giving us place to start.

Dan

Patrickt,
My partner wanted me to pass this question along to you:

With switch off no power from green wire to the one way diode side. Out of diode to blue wire with white strip. The blue with white is already hot 12v. I understand it to needs 12v switch power. So why is it hot on the out going side of diode. Dan forward this please.

Thanks,
Dan

It's hard for me to tell why you have the readings you do. But what I can tell you is the traditional and correct way that a voltage regulator with a charging light is wired. If you take that same voltage regulator and decide you didn't want to use the charging light, or it was in a car without a charging light, the wiring to the voltage regulator would be slightly different. It's important to know both of the wiring methods just so you can spot any mistakes. It's also not uncommon for a voltage regulator to be bad right out of the box. So if you confirm your wiring connections as being correct, and you still have bizarre behavior, a bad voltage regulator could be the cause. Here are the two basic wiring schemes for your I, A, S, F voltage regulator:

With a charging light:

I on the VR connects to the charging light (the other connection on the light goes to a switched positive source)

A on the VR connects to a switched positive source

S on the VR connects to the STATOR terminal on the alternator

F on the VR connects to the FIELD terminal on the alternator


Without a charging light:

I on the VR is not connected to anything

A on the VR connects to a switched positive source

S on the VR connects to a switched positive source

F on the VR connects to the FIELD terminal on the alternator

If you disconnect your alternator leads, and your VR leads, and confirm that your switched positive sources are being applied properly, then your charging light should not be coming on. Double check, then triple check. Only then consider the possibility that the VR might be faulty.

Thank you Patrickt, I really appreciate it. I'll let you know how it turns out.

Dan

You are using a classic 4 wire alternator correct? Not a one wire unit?

Blas

Hi Blas, yes it's a four wire.

Dan