testing fuel temp and oil pressure left side cluster

[samboyellowsub]

I'm wanting to test a left section of a 123 instrument cluster so I pulled out an entire instrument cluster unit in a working vehicle and plugged up the test piece to its harness and I'm not sure that if this is a proper way to test it or if it needs to be attached fully in order to determine if it works.
The reason I ask is that I now notice two metal tabs on the right edge of that piece that look like they hook up electrically to the middle (speedo) section.

Without hooking it up fully, the temp gauge does move but it maxes out when I put on the brights, and the fuel gauge goes up to "full" position when I start the car (i don't recall what oil pressure gauge did). I remember it working when it was taken out but it's been in a storage room bouncing around for a few years. Nothing is broken or bent so I think it's been alright but just want to make sure.

Anyone with a super keen sense of the electronics on the car would be of great help.

Or if you know a way to test it with a multimeter.
Thanks