I need some help. I have a 1990 IROC-Z with the 5.7 350. The person that owned the car before me had installed a aftermarket tach and now I am wanting to do the same. I believe there is some wiring left over from when he had installed it and I have included a picture. Could anyone tell me what wire goes where or what I need to do to get it hooked up? Thanks!

 

well...without instructions i can't be 100% but i think the red and black are hot and ground, the green is the trigger off the dizzy and the white is for lights off the dimmer.

 

Yes thats what the instructions say, but what about the wires that are already in the car the gray and black? Can I use those is one of them the one that attaches to the green?

 

Grey and black are for lights controlled by the dimmer (dash lights, shift indicator light, etc.). I'm pretty sure that what's in your picture is a light that goes in the bottom of the dash, just below the center vents. It points down to illuminate the ashtray, climate controls, etc.

In the motor compartment, the trigger wire from the distributor is brown. It's probably the same in the dash, but I'm not sure.

 

I think you are right about the brown wire for the trigger under the dash.