On my 1975 258 there is a red wire w/wht. tracer that is on the back right corner of the head as you face the Jeep. I believe thats it, because every time I unplug it to do a valve cover gasket, the coolant gauge doesn't register. Hope it helps.
'84 CJ-7, 6" lift, 33" BFG's, I6, .030 Over, Comp Cam, 400cfm Weber, K&N, T-18, 4 Core, Snorkel, D60 Detroit, Custom CV Driveshaft, 1350 U-Joints, D30 True Trac, Alloy shafts, S.R.S. w/ buggy springs, Custom Folding Shackles and Spring Hinges, Custum Tire Rack, Designed On Board Air, Optima's. Sneaky Jeep Owner #3.