So I've searched for hours on this forum and others to hopefully find someone who has already fixed some of these issues with no success, so here is the general problem and my "diagnosis" (I would consider myself a novice so I'd appreciate any help)

I bought an 89 5.0 TBI 5 spd last summer and over the course of the last year put a lot of work into. It had a check engine light and in trying to get rid of it replaced a lot; TPS, Map sensor, EGR valve, O2 sensors , ECM, Cat converter, you name it I probably replaced it. Now a year later the check engine light is gone. Problem now is that I think there is a short somewhere that I can't find, because the engine starts shaking and feels like the knock sensor(replaced) is retarding it, UNLESS I have both the fans blowing from the heater, AND the headlights on. I've looked everywhere for the short but cant find it, and it isn't a bad ground either as I've placed a few grounds from the engine to the body. I'm not sure if it's related but the tach isn't working either. I've read those are notoriously bad but usually they are just off. Mine is just dead.

Anyone have any ideas as to what it could be?

Sorry for the novel and I appreciate the help