I am just re commissioning a 1965 Series IIA with a diesel engine. As part of this process the engine was replaced with a series 3 model in standard configuration.

Question is how do the heater plugs operate on this motor. I have not yet had it in cold weather but I cannot trace power to them. It has the standard diesel ignition switch and there is no separate switch to operate the heater plugs.

Is there some sort of thermal linkage in them where they will not operate unless it is cold?

Thanks,
Steve