Tachometer signal erratic

[pdqford]

also, as far as the wiring is concerned... the way i had initially wired it was correct, where the gauge wants to see it's RPM information from the "ground" side (black/white) of the coil leads, not the battery side. which is confusing after this whole discourse, because the instructions say to use the "positive pole" but I tried to use the battery side wire (orange/white) and the gauge read 0 RPM while the engine is running.

That’s because the voltage at the + side of the coil will be battery voltage with reference to ground, while the voltage at the ground side of the coil will also be battery voltage when the coil is “off” (aka open circuit voltage), but will be near 0 volts when the coil is “on” as most of the voltage will be consumed by the coil. The gauge will be looking for the rising and falling voltage of the ground side to determine rpm.

[eil]

resistor plugs arrived in the mail yesterday, I installed them and also tested the digital tachometer, and everything works.

Excellent! Glad you got it all working and thanks for coming back to update the thread. (And I might add, it feels good being right once in a while!)

A lot of people underestimate the importance of those resistors. These days removing them means messing up nearby electronics in mysterious ways. As well as ticking off any ham radio operators in the neighborhood.

[CincinnatiKid]

Excellent! Glad you got it all working and thanks for coming back to update the thread. (And I might add, it feels good being right once in a while!)

A lot of people underestimate the importance of those resistors. These days removing them means messing up nearby electronics in mysterious ways. As well as ticking off any ham radio operators in the neighborhood.

it's ok to be right once in a while, but its also incredibly typical to be suffering woes caused by your own hand!

and i now have respect for the purpose of the resistors, but to be honest, the Captain Chaos in me was secretly hoping to be invisibly interfering with people's car radios while passing them on the highway. A former teenage anarchist can dream.