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1977 New to me 4386 - Needing help with electrical demons for display

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3 hours ago, J-Mech said:

The single electrical plug switch is either for a light or a gauge.  You can't tell by looking at them, so make sure you know which is which.

The sensor near the oil filters with multiple wires is for the tach. 

Should be another switch on it, right side, for the gauge.  It seems the light runs through the multi wire switch.  Sorry I can be more definite, but I can't remember and I don't have a book for them here at home. 

Why not tell the op to test with an ohm meter? You can certainly tell that way. Often the switch is physically smaller too from what I have seen. 

So the switch for the light will have no resistance from the terminal to the metal case if you measure it with a ohm meter at zero psi and most will switch to open at around 10 psi if you wanted to connect to a pressure regulator and use air pressure. The sender for the gauge will read around 240 ohms from the terminal to metal case at zero psi and if you would connect to a pressure regulator and take it up to around 100 psi the resistance would drop to around 33 ohms. This is also how you would test your original ones to determine if they are functional or not.

Most DT applications the oil sender for the gauge is just in front of the fuel filters and is in a tee with the lube line to the fuel pump if I remember correctly.

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Thought I’d share something for future readers, while reading my service manual I came across these schematics for the display and low and behold the one for the early serial number tractor matches what I was measuring on the pins and shows the oil pressure switch. So including that schematic plus the one for the newer display 



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