read engine rpm from battery/alternator???

[Frank F Parker]

> -> On a GM altenator, there are 4 pins, one big and 3 small. The 3 small
> -> are L for lamp, F for field, and an unlabeled one that we used in a
> -> GM race program where rules would not let us use a wheel speed
> -> sensor. That pins outputs a frequency proportional to rpm which we
> -> used with some engineering math to get vehicle speed.
> 
>  Is that the same pin that GM Diesels used for 'tachometer' output?
>            
That would not suprise me that is true. It has been a long time, but
I believe a Delco engineer told me they added pin for their own internal
testing purposes among other things.

regards,
frank
>