Help, Found unknown plug!!!
 

I just got down installing an 81 3.0 into an 82 911. Over by the relay board there is a plug that I could not find the mate to. The plug is 3 wire, blue, brown and black. They look like they are for a volt reg, but the alt has a Valeo alt with it built in. When I got the car started, the batt light was on, can anyone tell me if there is a plug, or do I need to change things. The wiring on this engine was for the 81 engine, and I am not sure about the alt, whether it was in the 82 or 81. Engine runs great, on a new rebuild.

Thank you for any help

If the new motor you installed has the Valeo internally regulated alternator there should not be an issue. Its quite possible your new motor has a bad alternator and is not charging. Start the motor and put a volt meter on the battery while running. You should be seeing approximately 13.75 to 14.25 volts. If less (like approx. 12 volts or less) then there is your answer.

I know the alt is good, because I loaned it to a buddy who was working on an 81 with a bad alt, and mine worked find 2 weeks ago. I wonder if the ground strap off the block has a bad conection, I did paint the fan and housing. I will check with a mutimeter in the morning and see what it is doing. The batt light is on.
Thank you

Welcome. Here to help.

I have been out in the hot sun all day, my mind has gone blank. I am just happy to hear this thing run after a few years of having it.

Well, it turned out being a bad ground. I cleaned a spot off, put it back together today, and now the light is out. Thank you very much for the help.