Early A body Fuel Gauge Instrument Cluster Question.
I installed an external regulator on my 3 Mopars. Did the cluster on my 1965 C-body a few months ago. I wouldn't use that old thermo-regulator shown since you can buy an adjustable electronic regulator which is much better. Many suggest RTE. Its main advantage is a quick heat-up of the fuel gage, which was an artifact of the old thermal regulator, but costs >$50. If you can tolerate ~1 min for the cluster gages to settle, any 5 V voltage source will suffice. Photo for my 1964 Valiant cluster. I used to find by searching "voltage limiter" with "Plymouth" on ebay, but this year nothing showed. I did find generic 12 V to 5 V adjustable regulators for <$10, which looked like what I had bought for $30 previously. I might buy a big lot and flip them as "Mopar limiters" on ebay. The voltage adjustment lets you get either fuel or temperature gage to read perfectly, but not both. I had to add 10 ohm in parallel with the fuel sender to get both zero and full correct on the gage. Also, test the temperature gage while the cluster is on the bench, using test resistors (chart below). There are slots in the gages to insert a screwdriver and twist to change the zero and range, but likely only done by the gage manufacturer in final testing, so "not advised" though I did tweak mine a little.
I think the TS-18 temp sender I put in my 1965 Dart has 185 ohm at 201F and 3400 ohm at 70 F, but info is sketchy. Since your gage has just tic marks, you can "calibrate yours in place." If you know your thermostat installed, its setpoint should be about the actual temperature once it reaches steady-state, so the corresponding needle position on the dash gage is about 180 F or 195 F, depending. But, the T-stat doesn't control to a perfect setpoint (proportional droop, read an engineering text on control theory), so will settle a bit high if a high heat load (driving up the mountains in summer) or a bit low if freezing outside. You might also use an IR gun reading on the engine block.
I installed an external regulator on my 3 Mopars. Did the cluster on my 1965 C-body a few months ago. I wouldn't use that old thermo-regulator shown since you can buy an adjustable electronic regulator which is much better. Many suggest RTE. Its main advantage is a quick heat-up of the fuel gage, which was an artifact of the old thermal regulator, but costs >$50. If you can tolerate ~1 min for the cluster gages to settle, any 5 V voltage source will suffice. Photo for my 1964 Valiant cluster. I used to find by searching "voltage limiter" with "Plymouth" on ebay, but this year nothing showed. I did find generic 12 V to 5 V adjustable regulators for <$10, which looked like what I had bought for $30 previously. I might buy a big lot and flip them as "Mopar limiters" on ebay. The voltage adjustment lets you get either fuel or temperature gage to read perfectly, but not both. I had to add 10 ohm in parallel with the fuel sender to get both zero and full correct on the gage. Also, test the temperature gage while the cluster is on the bench, using test resistors (chart below). There are slots in the gages to insert a screwdriver and twist to change the zero and range, but likely only done by the gage manufacturer in final testing, so "not advised" though I did tweak mine a little.
I think the TS-18 temp sender I put in my 1965 Dart has 185 ohm at 201F and 3400 ohm at 70 F, but info is sketchy. Since your gage has just tic marks, you can "calibrate yours in place." If you know your thermostat installed, its setpoint should be about the actual temperature once it reaches steady-state, so the corresponding needle position on the dash gage is about 180 F or 195 F, depending. But, the T-stat doesn't control to a perfect setpoint (proportional droop, read an engineering text on control theory), so will settle a bit high if a high heat load (driving up the mountains in summer) or a bit low if freezing outside. You might also use an IR gun reading on the engine block.