i have a tachometer and i got it hooked up to my pontiac sunbird?

[Dylan]

i hooked to the coil it has an electric coil but when i start the car in revs up to what it should and then the meter starts jumpin but the engine is at a constent idle and when i slowly step on the gas pedal the tachometer drops to the actual rpm reading and when i shift it jumps to

 

[melsg5]

how many wires are on the tach and where did you connect them specifically. You said coil but didnt say which side.