… the auxiliary cooling fan.
My tech bud tried shorting the thermostatic switch yesterday, as suggested, and the fan came on and ran very smoothly and quietly. However, I would point out that before that happened he could only get a faint “click” from somewhere in the engine compartment each time he tried, until he hunted the sound down to one of our famous Jag “multipurpose relays” which was purposed in this particular case for the thermostatic fan. He pulled another m.r. from the relay bank to swap out temporarily and the fan started right up (his multi-meter check of the relay showed later that in fact it - an OEM Jag one, btw - had bit the dust).
The only thing that worries both of us about the fan, being that neither one of us had ever heard one of them run before - is that when shut off, just before it stops rotating, there is a faint “tick tick tick” sound. For some reason, he seems to think it may be normal for that fan. Is it?