I've hooked up a cyberdyne fuel gauge, its got the for wire setup like so:

==Red -- Live
==Black -- Ground
==White -- Sending unit
==Purple -- Dimmer

The dimmer wire in all actuality, only serves a link to its configuration mode. When you put 12v to it, the gauge will flash prompting you for the size of the gas tank. Their is a screw/potentiometer in the back that you must twist left and right (VERY SLOWLY) to change the fuel tank capacity (6G-55G).

Basically, you set the gauge when the 12V is connected, leave the value their for 30 seconds or more, and then turn of the gauge. That is supposed to maintain the setting. Well when I unplug the purple and connect the sending unit, the gauge will drop itself to 12G-14G (which is inaccurate)

Has anyone else had this problem, and does anyone have any recommendations on how to get the gauge to stay at its specified setting ?

Let me know if you figure it out- I plan on getting one soon. This makes me really want to make my own though.

It seems pretty accurate, however that potentiometer in the back that is used for adjustment is extremely sensitive. I'll post if I find a resolution to this.

Have you tried to hook up the sending unit without unplugging the purple wire? BTW, the fluid capacity for the 87 tanks are as follows.

Fuel injected = 58.7 liters or 15.5 gallons
Non- Fuel injected= 60 liters or 16.2 gallons.

Actually yeah, thats how I ended up setting it. The damn gauge would change when I had the sending wire connected. I set it to 15G (does not allow for major accuracy, so i'd rather err on the side of having more gas than it claims) . After I turn off the gauge, disconnect the dimmer and reconnect the sending unit, all seems good for a while. Then when I turn of the car, and turn it on again, the gauge will have a different reading (claiming that it is full), and upon going into the config mode again (with the sending unit disconnected, it is down to 12G or so. Its really annoying.