1990 K5 5.7 TBI with no stock tachometer installed. I am going to buy an aftermarket one at autozone or checkers or whereever.....But, the question I have is I read that the signal for the tach comes from a lone white wire off of the ignition coil. I looked tonight and found a white wire that leads from the coil and goes no where. The wire has a connector to it, but nothing to plug into and my guess because my truck did not have a stock tachometer?? true? So, is it that simple?? in regards to aftermarket tach...red wire to 12 volt ignition source, white wire to dash lights, ground to ground and i think green to tach signal at that empty white wire off the ignition coil?

 

dumptruck1990, your assumption sounds correct. But if your truck didn’t come stock with a tach, it may not have any dash light for the tach "white wire to dash lights". I’ve attached a schematic for a 1997 CK-truck for your reference, sorry I didn’t have one for your year, but the 1997 schematic does match up with the information you provided. Hope this helps.