Tach Problem

[snoboardcore]

Hey guys my tach jumps all around from like 3000+rpm when u really hammer into it. The tach will go to 5 then 2 or 3 or 6 then to 3 anyways it jumps all over the place. I look at my monster tach and thats does the same thing. What do you guys think it could be? Possibly my coil?

 

[95opal]

sounds like you have a bad ground somewhere.check ur ground wires its more than likely your culprit

 

[seijirou]

Hey rather than making a new thread I might as well post my quesion in this one.

My tach reads too high. The car is an 86, but the interior is from an 87. I think somewhere in the wiring something is missing, crossed, or something.

The best way I can describe the problem is if you can imagine what would happen if you put a tach calibrated for a 4cyl car into an 8cyl car. It just reads way too high, and sweeps way too fast.

I do know that the 86 tach has a selection switch in it for 4,6,or 8 cylinders. The 87 doesn't have this feature. I think maybe there is supposed to be resistance in the tach signal wire that I don't have, but I'm really only guessing. And I don't know where the tach signal wire actually is.

 

[snoboardcore]

where are the ground wires located