i bought an after market tach due to mine being way off...the shiftlight on the new tach works but the neelde isn't moving...is it possible i didn't hook the green wire on the new tach to the right spot...due i need to disconect the factory tach???.. it is a 91 rs 5.0 tbi....thanx....bobby

 

I put an aftermarket tack in my 85 camaro before it got T-boned.
The tack wire should be the inside wire in the two wires that hook up to the distributor.On one side you have four wires and on the other side you have two wires you are going to tap into the inside wire of the two wire set.
The outside wire is a 12v+.
I would not think it would matter if you had the stock tack still hooked as you are just using it for a signal.

 

problem solved...the needle was stuck on the stop pin ...i didn't think it had one...works now... roughly how many rpms are you stock motor guys turning when in 5th gear going 60 mph??? and 4th gear...that way i can see how acurate new tach is...thanx