When I stuck my 60mm Apexi rip off tacho on my 87 Brumby it read way to high and bounces a lot. I tried buying a brand new condenser and placing it between chassis and coil negative, no luck. Tried a 10k resistor in series with the sense wire, no luck. Tried a in4004 diode in series with it, no luck. But when I hold the coil negative and ground (feeling what feels like 30 to 50v AC tingles) the tacho goes steady and accurate... What gives? Is there something other than a condenser I need to absorb this AC current?

Is the coil on its way out?

Car runs great. I tried another coil, a Bosch, and it made the tacho read even higher but with the same amount of variance jumping around

probably a dumb question but is the tach designed for a 4 cylinder? I know some are specifically for 8 cylinder engines. or maybe and unsufficient ground.

Edited April 5, 201412 yr by Mykeys Toy

It is adjustable for 3, 4, 6 or 8. I've tried it on all settings, the position of the needle changes but still erratic and well above where it should be bouncing more than a 2000rpm difference

sounds like an issue with retailer I have had that tingle off the back of my L tacho green tacced on my Brumby steering column - not a sensation the body wants to continue with - but I'd say is normal - how long did you hold it to keep tacho read nice ??

You'd think a dicky HT lead may cause this - if you also had a miss. Got any leads to swap in one by one just to see if any change?

I held the lead for about 10 seconds, wasn't comfortable but as soon as I held it the revs read right and continued to until I let go. I swapped all the leads with another set, but not sure if they were ok or not. One thing to note with the other leads is the tacho reacted exactly the same, reading between 2 to 4k at idle.