wiring alt tach signal to gas factory tach.

[JHyneman]

I have been having some problems with my tach on my repower. I have repowered my 89 firebird with a 4bt. I hooked up the alt tach to the factory dash tach and it reads 4000 rpms at idle. when I am cruising around I am guessing about 1400 rpms the tack reads about 7000 Rpms. When I am running about 2000 rpms the tach is maxed out. I can't even get a consistant reading on the tach because it is usually tached out. Can I wire my signal to the factory tach or do I have to buy a diesel tach... HELP!!! I am pulling my hair out trying to figure this out.

 

[Scot]

The difference is that the Cummins alt has more poles in it than the Firebird alt had. Figure out how many the stock one had and see if you can find some high amp aftermarket alt you can adapt in.

 

[tlgdiesel]

The original tach ran off the ignition system because the car was a gas engine. All the guys I have seen do this have been running a stock diesel tach, in the gm trucks with the diesel the tach runs off the alternator and were designed that way. Dakota digital makes a module that is designed to run a standard ignition tach off the alternator. It also allows calibration so you can get your tach right on, but you need a photo tach to do the calibrating. Your alternator isnt the problem. Go here you need a DSL-1 Universal Diesel Alternator Tachometer Interface

 

[JHyneman]

Thanks guys I appreciate the help.

 

[RSP]

Does anyone know which terminal is the W terminal on the back of a 93s alt?

I know on my Ford I had to go in a solder a wire to one of the field poles to make it work but I hope i dont have to on the Cummins Alt.

 

[PToombs]

Yup, you gotta add a w wire in. There is a good thread on here by me with pics on how to.



Found it https://www.turbodieselregister.com...1993/132600-wiring-alternator-tach-drive.html

 

[RSP]

Thank you, That worked.

 

[PToombs]

Your Welcome, good luck on your conversion!