Mystery wire.
So this leaves the unattached mystery wire with the straight connector. There doesn't appear to be any more unattached sending units on the engine remaining. The oil pressure guage needle responds so I assume its plugged in in the rear of the engine in the vicinity of the glow plug controler module. Upon closer examination, this mystery wire may be something I was trying to rig up for some forgetten reason (it was close to ten years ago). It'll be up to me to trace this one down.
Well, as long as I have the warning, temp and pressure indicators working properly, I'll be happy. I'll have to dig up some troubleshooting procedure to verify the engine sending units/guages are operating correctly. I hate to find this out 90 minutes west of Denver.
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As the saying goes, there are three things that go bad as you get older: One; Looks. Two; Health;