Thermopile, M14-P, Cylinder Head Temperature
Often attached under the rear spark plugs for cylinders 4 and 7 on a Yak 52, these Thermopile assemblies put out the low level voltage that drives the Cylinder Head Temperature gauge.
This low voltage output requires the total resistance of both the Thermopile and its attached cabling to be matched or very similar total values. For this reason the harnesses are made the same length for both cockpits.
Look at the rear plug on cylinder number four on the Port wing side of the engine compartment and you can feel this Thermopile through the insulation.
On the same Port side upper engine bearer, you'll see this harness for the front cockpit CHT folded up to store the extra length. On the Starboard side of the engine compartment this harness runs from Cylinder 7's rear spark plug directly to the rear cockpit.
The beauty of a healthy Thermopile?...it creates its own voltage when heated, providing a CHT reading even when all ship's power has been switched off.
If you start getting erratic or low CHT readings in the Front cockpit, suspect a ground somewhere in the bundled up section of the Port side wire harness - because these Thermopiles very rarely fail.
A short to ground from just a small break in the cable's insulation will reduce this low voltage signal to a meaningless CHT readout - not a number to be ignored in flight!
Your Thermopile can be disconnected as shown in the photos and tested using a DC multimeter across the two offset connectors. With the copper ring placed in heated water, if you do not see a climbing voltage that plateaus somewhere near 2v DC, your Thermopile unit is finished.