i have a 1990 full size blazer that i just recently bought and i was wondering if anyone could help me. I need to install a tachometer and i have no idea which wire i need to hook it up to. It says that it needs to go to the neg wire of the ignition coil but my ignition coil has four wires comin out of it.... If anyone knows which wire im supposed to hook it up to please let me know.... thanks

 

Welcome to the forum
Your distributor has 2 terminals close in at the cap and 2 further out. On the outer 2, one is a red (battery power) wire, the other is either not connected to a wire, or there is a brown wire connected. If you look closely, they are marked "batt" and "tach"
I have to go to work now and don't have time to look for or post pics. I'll check back tonight and see if you got it sorted out.
Hope this helps
Oops, it just occurred to me that you may not have the system I was thinking about (with the coil in the cap)
Is your coil mounted seperately on the intake manifold?