The oil pressure light is controlled by a switch in the ground side of the circuit. To work your gauge needs to have a light that is connected to power and lights when you connect its wire to negative.

In my cheapos I used the parking brake light for that because they didn't have oil lights. It worked OK but I always wondered what they were designed for that has a parking brake but not an oil light or neutral light.
The Danmoto has an oil light and a neutral light that work perfectly.

Did I mention that almost every wire on the Danmoto matches Honda's colour code? The cheapos had different colours between otherwise identical looking units...

 

Ok then it looks like this gauge won't be able to detect an oil light in that configuration. The only ground coming off of it is a main ground and to I interfere with that would interfere with the rest of the gauge. Luckily I can simply attach a bulb that takes 12v and bada boom not fancy but works, right?

Sent from my HTC Desire 510 using Tapatalk

 

If it has an oil light it should work the way I described. That's a pretty standard way for them to work....

The switch finds ground by being screwed into the engine block so it wouldn't need aseparate ground wire.

 

This is the same gauge I use on my GN400. Works great. You can also hook the fuel indicator up to most temp senders and use it for a temp gauge.