My Dad and I took on a project of replacing the blown motor in my 1986 740 turbo with one that has low miles from an 87 740 turbo...We got most of the wiring to match and it runs pretty good. But - the temperature guage is not working.

The wiring harness is a combination of both 86 and 87. I believe that the temperature sending unit(in the engine block) is from the 87 and has two connectors. One wire is black/yellow. The other is white/yellow. It may also be helpful to know that there is a black/yellow wire (as well as a blue one) from the 87 (?) harness that doesn't have a mate with the 86 part of the harness that runs to the inside of the car. ANy help to mate the two harnesses to get this solved would be greatly appreciated. Would this also have an affect on the coolant temperature sensor as the electric fan has been tested and works...it just doesn't come on under normal conditions - only when tested. Help! Thanks in advance for helping me with my latest challenge.