[Fedup]

I may be out of line here but I have to question what it is that makes you sure you have a 5610s? Everything you describe and the photos you posted indicate you have a 5610. The only thing I see that shows otherwise is the paint color. The s models did come with the dark gray chassis color, not the standard Ford blue. There were some tractors that had a big black S on each side of the radiator shell. I'm not really sure what for. Could yours be one of those?

 

[Fedup]

Well whether it's a 10s series tractor or not is not important in this case. What you want is to make your thermostart active, right? All that needs is a fuel supply. I believe the fitting on the heater unit is just a compression tube type, I think it's 3/16". All you need is a length of tubing (steel maybe, also could use copper) with a compression tube nut and ferrule. Swing out the battery and look at the fuel return lines leading up to the tank filler neck. There should be two. One comes from the injector return, one comes from the pump/filter base. They may join together somewhere, or may each go to the filler neck separately. Probably plastic. You want the one from the filter. Pick an accessible spot ( hopefully above the level of the heater unit), add a tee fitting into that line and run another line to the thermostart. That's basically all there is to it. The hardware is your choice. If the line is flexible enough you can use a plastic vacuum line tee from a parts house. You can also use compression tube fittings if the line is too stiff for that. How complicated you make this is totally up to you. All you're trying to do is create a small supply of fuel under very little pressure that can more or less gravity feed the element. If the unit functions properly when power is applied, that's all you need.