I bought a Raptor shift light, and can't decide if it would be better to put it on an injector signal or not. I have an OBD1 PCM, so I'm not sure if there would be any speed issues.

(also, does anyone have a link or can tell me how I would connect it to an injector, and which one?)

 

It will be just as accurate with an injector pulse signal as it would be with an ignition signal. You will see the shift light come on before the tach reaches the shift RPM in the lower gears due to tach lag.

 

Generally you take the tach signal off the coil. The coil fires 8 pulses per 2 crank revs, the injector fires on pulse per two crank revs (unless its a 93 and fires twice per two crank revs). There is no reason an injector would be any more accurate than the coil, or the tach output signal on the PCM. They are all based on the same source of data, which it the output of the optical sensor in the Opti.