tach help/advice make waves instrument corporation super pro

first off thanks in advance

1970 dodge dart swinger original slant 6 car and now a v-8 and all stock electrical/ignition stuff was swapped over from the 74 swinger parts/swap donor car.

i have looked online and here and cant seem to find much relating to current problem. it is a super pro 1288 tach and have it wired as instructed.it is a new install and i have checked all my connections including the coil to engine ground and also tried another coil.


white-light switch
green-negative side of coil
red-switched power direct to the fuse box
black-to negative side of battery
switch set to 8 cyl

at an idle the needle stays on zero until i rev it up and it jumps from zero to around 1000 then seems to work nornal from that point up. and when when let off the gas and rpms settle to less than around 1000 it drops directly and fast right back to zero

i hope i included enough info for you to help

thanks don







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