Components and "how to" for a CJ temp gauge dipstick by Murray Bowden
Firstly, you will need to measure from under the head of the filler plug down to the full mark on the dipstick. This is important because the oil level is measured with the threaded portion of the plug removed from the case and the plug resting on the surface of the engine case. I add this because I made an adaptor which meant I had to adjust the full level mark.
The temp gauge has a 1/4bsp thread and screws into the top of the adaptor. I threaded the adaptor to fit the filler hole in the engine case. The gauge has a 1/8"probe which was the same diameter as the CJ dipstick. I found an extension spring which slipped nicely of the probe and dipstick.
I soldered the gauge probe into the spring, going halfway down the spring's length. Make sure that the inside of the spring and end of the probe are really clean. Be sure to use soldering flux so that the soldering process is really quick and can then be quenched in water immediately to prevent damaging the gauge by getting it too hot. I added this because I don't know what gauge you will get.

The gauge I used is not ideal as there is too much information on it. The numbers are small. The rider needs to be able to glance at the gauge quickly and get the temp. My bike has hit 100°C once on a 30°C day on a hot tar seal road, so I don't know if it will ever get hotter than that. So, if you get a gauge that reads 200°C maximum, then the 100°C graduation will be at the 12 o'clock position and easy to see that the temp is OK from a quick glance.
Once the spring was attached to the gauge I inserted the end of the dipstick into the spring so that it butted up against the end of the gauge probe.
Before you solder it in though be sure to have the correct dimension from the underside of the adaptor to the full mark on the dip stick. Again make sure the end of the dipstick to be joined is clean. Repeat the soldering and quenching process. I found another spring that was slightly bigger than the one holding the two pieces together and wound it over the spring joint to stiffen and strengthen the joint a bit. I did this because the wire gauge of the spring was quite thin. If you find a fairly sturdy spring then one will do.
The last thing was to use a piece of electrical shrink sleeving to cover the joint and stiffen it some more. I didn't know if the joint was going to hold together so I probably over compensated. If I was to do the job again I'd use a 1mm or 0.40" spring. It would be one spring and nothing else.
The heat is transferred from the dipstick to the probe of the gauge very effectively by the spring which also gives it the flexi action required to get it into the engine without hitting the tank.