I got a question. I have a 94 Civic DX, the edition that does not come with a stock tachometer. I put a 4 inch tach in there, and the other day, I had my 2 12" subs on and my RPMs would jump according to when the subs would hit. This isn't supposed to happen, is it? Any ideas? Should I go buy a more powerful amp?

 

try to connect the tach wires to another 12v source and see if works.check for false contact on wires.

 

also, if you have a hard hitting system. you tach is prolly bouncing to the bass....aftermarket tachs are usually more sensitive to out side force than stock guages..but i had a similar problem with my speedo...it would move about 2-3 mph during bass hits if it was turned up. but i would check what the other guy said too.