As the subject says, the car runs off the battery when I start it up. Once it gets revved above 3K for the first time I see my volt meter go up and lights get bright. Then the alternator picks up the load until I turn the car off again.

My electricity hateing mind thinks it's something that the alternator needs an input that the engine is running before suppling the field currect to the stator to prevent draining the battery when the car is off or something.

Any ideas on a fix? The car is an 86 with a 87 turbo swap (using turbo right side electrical harness and ecu) Thanks.

 

sounds like the sense and feed leads to the alt are backwards

 

See if the White wire with a Black stripe has 12v on it when the key is to ON. The White/Black wire supplies the voltage for the field .........until the alternator starts putting out where upon the diode trio supplies the voltage for the field thru the regulator......not the white/ black wire. The Black/White wire is for sensing voltage for the voltage regulator in the alternator. Both wires should have 12v when the key is to ON.

Both wires are in the small connector on the back of the alternator. Both wires have fuses. The White/Black passes thru the CPU at pin K of the CPU. See jpg.

 

As has been pointed out, it's probably related to the connection on the back of the alternator. Do you get the "All idiot lights on" with the key on but engine not running? Mine did the exact same thing, and I figured out I had forgotten to plug in the rear alternator plug after I did some engine work.

-=Russ=-

 

Great info guys. I'll take a look into it.

 

I thought it was OK to get all the idiot lights on while the key is in the ON position but car NOT running. This way you can see if you have any burned out bulbs? My alternator has been doing funny things as well so I thought maybe I mixed up the wires in the back when switching to an FD alternator....

Anyway to tell if they are reversed? My alternator only seems to be struggling when the RPMS's are low/at night. Otherwise as soon as 900rpm + I get 14v.

 

I have the exact same problem,. alternator doesnt work until i hit 3k once,.. after that its fine for the rest of the drive,.. ill check the wires.