No trailing spark no tach
 

I am currently working a 90 GTU turbo swap with turbo EM harness turbo ECU with RTek 1.5 upgrade, S5 auto trans and ignition harness. I am having somewhat intermittent trailing spark and tach issues now its getting to be more often than not. start the car tach falls out immediately and no trailing spark out of the coil sometimes it the tach will stay and drop out after few seconds. I have not been able to check for spark while the tach is working. I have tried a known good trailing coil a known good CAS with no result. I have done 1 basic check both wires in connector F34 the 2 pin connector have power key on which is correct. as for the 4 pin connector im not sure what I should have on 3 of the 4 wire yellow w/ blue tracer goes to tach the other 3 go back to the PCM im not sure which or how many are triggers powers and grounds. another piece of helpful info in a momentary lapse of intelligence I connected the battery backwards and popped the main fuse which has been replaced and I believe this problem existed before that happened but cant guarantee it. the car has only had the motor and harness hooked up for a week or so and maybe 50 miles of driving. any help or thoughts info known problems would be great.

The coil/igniter needs to bolted to the fender properly for the unit to work properly as this is how it receives its ground. You might want to clean the surface where the coil mates to the fender. Also, low voltage in the charging system can cause the coil to cut out. The tach gets its signal from this coil so if the tach is working then the coil must be working. You also might have a bad spark plug wires or spark plugs as this could cause the coil to cut out.