Welcome
Not much to go on, I know of but have never encountered the Koso gauges.
The "extra" wires - are they from the gauge or from the SV harness? If they are from the harness, Suzuki's colour code is red for unswitched +12V (ie: live all the time) and black/white stripe is for ground.
I think black is for left turn signal.
Orange + any colour stripe is for switched +12V (comes on with ignition)
After a quick google the
koso dl-03s also uses red for +12V which implies you have disconnected its power.
Have you measured the voltage on the red wire (between it and battery neg)?
I read that Koso used to use the 3m splice connectors and wires can pull out of them if they weren't crimped sufficiently.