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Hi Steve. Delayed reply, but I've been out of town for a few days.
Yes, I thought through the two relay system pretty thoroughly as well. Aside from the extra complexity and having all the extra wiring, I want to actually sit and diagram it. However I'm in agreement, a second relay is required so that the ...shall we call it the power relay? for the fan is controlled by a second circuit for the OD fan cutout. The main reason I did not pursue this is because regardless of the "default on" position of the OD solenoid, there is also the issue that in regular driving, the bloody gearbox can actually upshift to OD 4th at a very low speed, or well below "highway" speeds. That is what really stopped me from pursuing it. Point being that I don't want the fan to cut out at 25, which is a speed that will regularly find the car in 4th. Up here our surface street speeds range as high as 60 (we are not very congested). However, if it's hot out, which it is at this time of the year, and the car was tooling along at 35 in 4th, I would still want the fan on (since it might be 105 outside). I want that fan running until the car hits, say, 50. In other words, unless the car is traveling at or near highway speed, I want the fan on. It occurs to me that what the second relay might need to trigger is is a sail switch or an ambient temp switch. Properly position (someplace, don't know exactly where) an ambient switch might be cooled enough by sufficient airflow to kick in the second relay, or just break the ground to the first one. A friend in electronics recommended a "track" sensor. This is conveyor technology. A proximity type switch that does not require a reflector which measures the speed at which a surface is passing. That type of switch could literally point at the roadway and measure velocity. Another possibility is a driveshaft sensor like the aftermarket cruise systems used to use. My goal is to find something that I can install right up front, near the relay I have right next to the mail terminal junction (by the battery) so that all my wiring is right there. By the way, I fused my circuit by installing another weather-tite fuseholder right next to the main system fuse on the "rail". I had the local trophy shot heat-emboss "FAN" on the plastic cover and "MAIN" on the other one. Do you remember Rover sedans? If so, you may recall "Icelert", the box on the front grill that measured reflectivity of the road service to warn of glare ice. The controls for this were mounted on the left of the dash. A rheostat and warning light. When I pulled my Rover engine and swapped to Nissan power I put in a big electric fan (for idling for hours crossing the border in Mexico). Though the fan had a temp sensor in the radiator,I used the wiring from the Icelert to put in a manual overide toggle switch in place of the dash rheostat. That way I could just turn on the fan when I wanted. I might just do that, though it's not the solution we are looking for of course.
I have my nephew, who works for a conveyor manufacturer in Switzerland, getting me some information on proximity sensors. I'll let you know what I find out. By all means do lets keep in touch as this is a neat project. This week's task is to finish fiddling with my new remote filter setup using the 740 Turbo thermostatic remote filter boss and additional 90 degree adaptor from Ford Racing (Ford parts....never thought I'd do that, but how apropos).
Dave
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