I have a ls-3 in my 61 Corvette with a GM harness and I need to find the trigger wire on one of the ign. coils to power my Speedhut tach. There are 4 wires to each coil harness, does anyone know which one is the trigger wire. my tach is programmable so all I need is the trigger wire from one ign. coil. For some reason it won't read the tach signal from white tach wire on the ecm. Thanks, Bob

 

Pin c on the coil is usually the right one.

 

How do I know which one is pin C on the coil, is it marked. Thanks, Bob

 

What ECM are you using? The E38 ECM is tried/tested to power factory and aftermarket tachs with some settings and a pull-up resistor.

http://www.hptuners.com/forum/showthread.php?t=36611

IMHO, stay away from cutting coil wires. I've seen several systems code when trying to tap them for a signal.

 

The connector will be marked with tiny little letters.

 

Thanks, I will take a look. Bob