Originally Posted by BagusJeep
The S post connects to that purple with tracer wire back to the sensor.
The + terminal is a +ve feed. As John Strenk pointed out it could go to the back of the speedo housing and join on to the red wire that used to feed the temperature and fuel gauges.
The other terminal surely must say - but it looks like +. this is a ground, depends on how your instrument panel is being grounded. If just through the metal of the panel etc it is will be uneliable. You may debate how to ground all your instruments but look at how the other gauges are grounded.
That black wire from the bulb also goes to ground.
This is exactly right.
Looks like the Meter can be used on either + ground or - ground vehicals.
Looks simple enough to attach the black wire to the - post and then run a wire from the - post to a ground screw on the dash. Either make your own grounding point with a self tapping screw or the speedo mounting bolt on the back of the dash.
Run the + post to the "I" terminal on the back of the fuel gauge like Bagusjeep mentions.
Run the red wire on the light to some orange wire on the back of the dash like 82JeepCJ7 says
First time I ever saw a gauge with metric and English markings like that though.