Which wires go where?, RPM Gauge...only 2 wires? Options

[jcambo7]

So I am finally trying to figure out why my rpm gauge doesn't work and I discover I can only find two wires...which makes no sense to me because their are 4 places on the back for wires. So I am just wondering if anyone has this gauge in their 914 and if they might know the answer to my wire predicament?
Here is the front

Here is the back

[Larry.Hubby]

I have a tach just like that in my car. It's a tach from a 930, and the small gauge at the bottom was originally a boost gauge that read either 0-1.5 bar (1977 only) or 0-1 bar (1978 and later). Someone has had North Hollywood Speedometer, or someone with similar skills, re-do the face, and perhaps the movement, of the small gauge to turn it into a gas gauge. The way to hook it up is with the red/white wire going to "+12" (the connection on the original 914 tach that this wire goes to would have been labeled "15"), and with the black/red wire going to the "TD" terminal (on the 914 tach, this would have connected to a terminal labeled "1"). The "G" terminal goes to the small gas gauge movement, and the other connection is a ground. If you want to use the small gas gauge, the green wire that used to go to the gas gauge in the combination instrument should be hooked to the "G" terminal.