1 Wire GM alternator and Generator Light

[Budman1758]

Searched most of the forums here and did not find an exact answer to this one. I have and old vehicle and have installed a newer 1 wire GM alternator in it. These alternators do not have provision for the "idiot" light on the dash. What I am looking for is a simple circuit that will trigger a relay to operate the light. I want it to light at just under 13 volts and go out at just over 13 volts. (or thereabouts)

I had thought I could just use a 13v zener diode but it seems to require a little more than that. I tried to put the zener inline thinking it would conduct "backwards" when the voltage went above 13 volts but it seems they don't work quite like that. There is an outfit that sells something exactly for this purpose but the voltage is set at 11 volts and they want 30 bucks and 10 bucks to ship the darn thing. Diodes are much cheaper. :>)

Anybody have a simple circuit in their back pocket that will do this? Any help would be much appreciated.

 

[MikeMl]

Don't have time to go find it tonight, but I have posted a circuit on these forums several times that uses a LM431 (TL431) which lights a LED on falling voltage. It has a very sharp knee (<10mV). Its orgininal purpose was to indicate that a battery was discharged below a level. It is adjustable with a pot, so could be adapted for your use.

Use the forum search with my user name to go find it.

PS Here it is Look at post #4 and read the entire thread...

 

[tcmtech]

Have you looked under the plastic cap that goes over the two spade connectors on your one wire alternator to see if they are there or not?

Many 1 wire regulator units still have both of those connection points and can have the original Alt light lead connected to one of those terminals sot he light will work like normal.