Tachometer Problem

[dbettner]

I have replaced my crossfire with a edelbrock high rise performor intake , holly carb and Mallory Unilite Dist. and Pro Master Coil. The Tach did not work so i replaced the circuit , it still did not work so I traced the neg. coil wire back from the coil and found a round cylinder type thing that looks like a resistor or something when i by passed this item the Tach worked perfect.
I drove the car all night with no problems.
In the morning when I started the car the tach. needle was on 2000 rpm and would not move.
I took it out and the needle move freely and had no burn marks on the circuit board so I hooked it up under the hood using jumper wires to make sure it had good signal from pos. , neg. , and coil neg but still did not work.
Do I need that resistor looking thing and if so what is it and where can I get one that works properly.
Thanks ,
Duane

 

[Robin7TFour]

DUANE, check with mallory ,you may need a signal adaptor. i am guessing, had the same situation when i put a digital ign on my harley and wanted an electronic tach.

hope this helps

robin

 

[Big Fish]

The resistor looking thing you are referring to is most likely the tach filter. This link will help you with that part: http://my.execpc.com/~rodney1/corvette/ The filter is supposed to remove the spikes that otherwise could damage the tach circuit board. It is very possible your new ignition system is not compatible with the original tach, I agree with the other reply, check with the mfr or vendor.