tach troubles

[booeman]

I just put a tach from a 74 sport wagon in my 71 sport coupe (manta) and when I power up the ignition switch with out engaging the starter the tach jumps up to 3500 - 4000 RPM's. it's wired according to the manual except I don't have an oil gauge. (red/black from the tach posi to the posi on the oil gauge.) I don't know if it matters, I have a hot spark electronic ignition that uses the negative side of the coil with the tach. anyone seen this before?

[tomking]

Search this thread as it sounds eerily similar to my problem, now corrected.

[tekenaar]

Red/black wire is just sw12V (comes on with the ignition key) . . .