I swaped a 94 7.3 idi into my 84 that had a tach that ran off the alternator. I was wondering if I could use the factory tach sensor off the 94 and wire it into the aftermarket gauge?

 

I too have an aftermarket tach in my 84, it uses the alternator pickup. I remember reading about how they work, it picks up a certain signal from the alternator. Can't remember exactly what, my guess is it won't work. You could temporarily hook it up and try it I suppose, see what happens.

 

if i remember correctly the stock tach reads off a magnetic pickup on the timing gear. 1 revolution on the gear reads one revolution on the tach sensor. the alternator style tach reads different and will not work.
maybe contact the tach manufacturer and see if there is a difference between the reading and how it will work switching from a 1G and a 3G alternator

 

That sounds right to me. My Autometer tach reads off the alternator. I looked into how it works when I bought it, it uses a two wire sensor that mounts to the alternator body on top of the separator rings. The sensor picks up the signal from the alternator and the tachometer converts it to another type of signal, I can't remember exactly what. Anyway once I had it hooked up I had to calibrate it to the engine. I used an optical tachometer to get a reading off the crankshaft pulley, then using the calibration screw on the back of the tachometer dialed it in. Actually pretty easy. I think due to the way the tachometer receives the signal, it probably won't work.

 

Dakota Digital makes adapters which will work with our sensors and standard tachometers.

The signal coming out of the factory IDI tach sender is a small AC signal at 53 pulses per rev.
So your adapter must be able to handle 53 pulses per rev and divide it accordingly.

 

Thanks guys. Guess I'm just gonna put it back on the alternator and recalibrate it. Just figured I would give it a try since it would probably be more accurate than the alternator.