Autometer Speedometer to TKO Wiring Question

[TTimmy]

Hi folks,
Do I need to wire up both the green (signal) and grey (return) wire to my Autometer gauge?

The prior owner had trimmed back the grey/return wire and the wiring diagram seems to indicate that it is NOT needed. I have TKX if that matters. Obviously, I would like to confirm this before I button everything up!

Thanks!
TTIMMY

[BUDFIVE]

TTimmy,
I found the gray wire needs to be grounded. See pasted text below from post #51 in my build thread:

Speedometer Debug, Clutch &Gears
-2 wires in RF harness and connector to TKX electrical speed sending unit.
-Obvious RF green wire labeled “speedometer signal” goes to speedometer “sig” input. -Not obvious what to do with gray wire labeled “EFI-speedometer signal return”. With it left disconnected (I have a carb’s engine) the speedometer doesn’t move (after its initialization) with driveshaft spinning. After reviewing Forum posts —The gray wire must be grounded.

Now the speedometer works although I haven’t calibrated yet.

[Nigel Allen]

I would be inclined to connect the gray wire from the speed sensing unit only to the ground wire that enters the speedometer. This prevents interference from stray ground currents getting into the speed signal circuit.

Hope this makes sense.

Cheers,

Nige

[nashuanuke]

hmm, I just noticed my speedometer had power but wasn't changing while go carting. I guess I know why now.

[Blitzboy54]

Yup, grey wire goes to ground.