Not satisfied with that, I decided that an additional manual switch to turn on the fan would be useful. I thought for a bit about the least obtrusive way to do this, and hit upon the idea of using the rear windshield wiper switch. The car used to have the rear wiper when I bought it, but when I ditched the tail, that went with it, leaving me an extra switch.
In order to do this, what you essentially have to do is ground the fan relay by means of the switch. I looked around for a way to do this near the relay panel, but couldn't find an easy way to do it without splicing into the wires themselves, and one of my electrical mantras is never to touch the factory wiring if it can be avoided.
The first actual interruption in the wiring from the relay to the t'stat is in the front right side of the trunk near the spare:
I reasoned that if I could find an identical connector, I could just fabricate a short connecting piece with an additional branch to run to the switch, and that would leave the original wiring intact. After a bit of searching around at my friend's shop, I discovered just the thing. Here's the connector I made with the yellow wire as a take off to the switch. The covered blue spade connector joins to a wire running to the switch. Underneath you can see the black bakelite connector for the fan's actual power supply and ground wires:
Here you can see the itinerant yellow wire making its way rearward behind the relay panel and back behind the dash:
Here it is emerging from the hole in the dash. The rear of the switch becomes much more accessible with the removal of the wheel and the oil temp\press gauge:
