You didn't say if fuel gauge works or not. all 3 thermal gauges operate on a single gauge voltage limiter. It is inside your rally fuel gauge. That's why your fuel gauge has 3 contact posts. Most owners wouldn't know which 2 of these 3 post to connect a tester such as this onto. Your fuel gauge also has a slither of metal on the back of it that grounds it to the inst' housing. Any inst' housing most have a chassis ground path back to battery negative to work. Hope this helps
