My solution is to remove an electric temperature gauge from a Saab combination gauge unit. I trimmed the gauge face slightly and mounted it on an aluminum plate, as shown above. Making the gauge fit the mount plate and the mount plate fit the speedo module....let's just say that part took the most head scratching.
Once you get one of these suckers apart, you have quite a few pieces. I've cleaned them all up here, and have repaired the inoperative odometer in this one, and it's ready to go back together. That's another the tricky part, as you might imagine...
Go back to the first photo [bottom] to see how the electric gauge looks when it is installed. It is a good "fit" and a good "match" for the other original gauges. This photo shows the back of the module, with the electric gauge mounted. The tan wire is marked "tank", but that's my mistake--I changed it to correctly read "temp sender".
All electric gauges--except an ammeter and a voltmeter--need 3 electrical inputs: 12 volts for reference, an input from the sender unit, and ground. The latter is the black wire in the photo. So you see, the head scratching worked!