Wiring a tach off alternator

[David85]

Did a diesel swap and am trying to figure out if its possible to wire the OEM gasoline tachometer off of the alternator. Its done this way on other vehicle brands and it should be possible here too. The idea is to use one of the three windings terminals as the pulse signal source for the signal wire on the tach. I'm wondering if anyone has done this mod before.

Truck is a 1988 ranger 4x4 and the original engine was a 2.9L EFI if it matters.

The diesel engine is a modified mitsubishi 2.3L turbo diesel (has a roller cam and newer model head now). There is a magnetic signal connector off the injector pump, but I'm not sure if that signal would be accepted by the tachometer.

 

[Bob Ayers]

You need to bring the signal off the winding before it's rectified with a diode.
The cathodes of three diodes will be commoned, connected to the B+ terminal. So, pick one of those three diodes, and get the signal from the anode terminal.

 

[David85]

Thanks, that fills in some of the blanks for me.