I've got an '87 Z-28 with the 305 TPI, with the 4-wire (2 plug) style of ignition coil. It has an issue with the tach wire grounding out the coil and preventing the engine from starting. If I disconnect the power/tach connector and jump the power (red) wire to the coil it runs fine. I've removed the tachometer and the problem persists, leading me to believe the problem lies between the instrument cluster and the coil.

According to my wiring supplement manual, there should be a tach filter consisting of a pair of capacitors that will smooth out the signal from the coil, but for the life of me I cannot find the darn thing. The wiring manual says it's located near the tach, and my parts manual doesn't even show that style of ignition system, only the coil-in-cap type. Searching on the topic got me a couple threads saying the TPI cars didn't even have a tach filter.

Any suggestions?

 

here is the location

https://www.thirdgen.org/forums/elec...ch-filter.html

 

So my car actually doesn't have a tach filter, the problem turned out to be a sloppy solder job along the tach wire by the P.O. that was shorting to another sloppy solder job on the battery wire. Fixed that up and the car fires right up, tach works great.