Originally Posted by
bradrs
Doing the tach swap might be simpler then, since the AEM doesn't seem to support it. Looks like it is mechanically correct. It would make sense if they were the same electrically, with only a change in scaling. But I'd probably still want to at least do a pin out and make sure I wasn't shorting something to ground or going to accidentally damage the cluster or tach. I'm going to search craigslist and see if I can get a 2g tach to inspect.
I just looked up the EMS instruction sheets, and the relevant pin (58 on the 93- ECUs) is not wired according to their instructions. Not even to a spare output. Yep, that's what I thought when looking at the instructions also.
The reason I was asking about the coil/PTU is you could still use it to trigger the tach since you kept the stock one. If you hook up a coil(just to test it) to the 3rd channel then get the AEM to fire that channel, it should get the correct pulse generated back to the tach. And if that works, then remove the coil and swap in a small inductor. That would basically be a tach adapter, like many CDIs use to work with the OEM ignitions. Lost you there:D