Part 1: Background and Description Part 2: Building the Tester Part 3: Demonstration of Testing Build a Gauge Tester Part 1 Testing the dash gauges has come up a few times here and on the Wagoneer forums. I look at the TSM and its obvious to me how to test using some clip leads and fixed resistors. The TSM was written for the dealership mechanics (called technicians today), and they had no qualms reaching into the dealerships' wallets by specifying a "Jeep Corporation Special Tool" for this task, regardless of how simple the tool might be. Here's the tool: Impressive looking. Likely a hinged steel box with storage for the captured test leads. The clip in the lid likely holds an instruction card or pamphlet. Of course, it has to stand up to long, rough usage, and be understandable to even the greenest line mechanics. Pretty sure all the figures and values came from my digital copy of the 1975 TSM. I'm sure that the '70s models are all the same (the Wagoneers got a redesigned dash in the '80s which changes the gauges, but the CJs should be the same to the end). Don't assume though - compare to your TSM. Here's the gist of what this instrument does, from elsewhere in the TSM. For the temperature gauge, there are some standard resistance values that substitute for the sensor/sender immersed in the hot coolant: For the fuel level, there are different resistance values: Here's the gauges' circuit: The tester connects to the dash at points T1 and T2, with the associated "sender unit" disconnected. I thought I might just demonstrate these tests with clip leads and resistors. However, one could build the J-24538 tester rather easily, so that's what I've done.