Aftermarket Tach ?

[69C10@16]

Picked up a tach off a friend. He had it in his 88 Chevy w/a 350 all stock. It worked great. I hook it up to mine, 12V, GND, Neg on Coil, and it doesn't read at all until I rev the engine and then it seems like it's reading too low. Maybe by 750 to 1000 Rpm's. But I may just be misjudging the RPM's. It may read fine. But why doesn't it register at idle. I realize that his 88 is going to be HEI and therefore be higher voltage on the coil but I figured the tach would still work on mine. Oh, number of piston switch is in the correct spot,8 (I have a 307 btw). I know I hooked it up right or I wouldn't have gotten anything.

ANY ideas?????????

[corn]

What brand is it?

[69C10@16]

Honestly, I can't answer that question, though I would love to know for myself. There is an odd emblem in the middles of the face that makes out to an MW. It goes up to 8K RPM. Is a four wire tach:

Green - Neg on Coil
Red - 12V +
Black - Grnd
White - Backlight

That is all the info I have on it. Any help would be greatly appreciated!

[rodnok1]

did you try moving the switch around, i had one that evrey now and then the damn switch would act up and i think it defaulted to 4 banger...

[69C10@16]

wouldn't that make it read high?? B/c it's seeing twice the spark for what it thinks is less cylinders? I would think it t o read twice as high. I'll try it later tonight. just to see.