Can anyone help me interpret a wiring schematic? (PIC of wiring schematic)

[KYKub]

The temp gauge on my G1900 has not worked since I bought it second hand. Never moves off the bottom peg. Cleaned all the grounds I can find, replaced all 3 fuses, and replaced the temp sender. No improvement. Fuel gauge, status lights, and hour meter work fine.

If I ground the temp sender wire a warning horn sounds (loudly!). Just about came out of my skin when the horn sounded since I didn't even know it had a horn! Needle didn't budge,although something must be working if the horn sounds.

Wondered about combination box, but from what I can gather it has nothing to do with temp gauge. Is that right?

Thinking I must have a bad gauge, I replaced the instrument cluster. Still nothing!

So, I now believe there is a problem in the wiring between the temp sender and the harness that connects to the instrument cluster wiring. I don't really know how to read an electrical schematic so I would appreciate any help. My specific questions:

1) Does the "Y" wire run from the temp sender directly to the second position, right side of the instrument cluster wiring harness? (see schematic) The one directly under the top position with an "X" (unused, I believe). it looks that way in the schematic, but then where and how does it connect to the horn?

2) Does anyone know what "I", "E", and "U" labels on wiring stations on the back of the temp gauge stand for?

3) In testing wires for continuity, would I check between the temp sender end and the harness end connection of the "Y" wire?

4) Do I need to test the "I", "E", and "U" wires? If so, can anyone help me understand where they go? I don't understand the schematic.



Thank you for helping me wade through this quagmire!

 

[MinnesotaEric]

The temp gauge on my G1900 has not worked since I bought it second hand. Never moves off the bottom peg. Cleaned all the grounds I can find, replaced all 3 fuses, and replaced the temp sender. No improvement. Fuel gauge, status lights, and hour meter work fine.

If I ground the temp sender wire a warning horn sounds (loudly!). Just about came out of my skin when the horn sounded since I didn't even know it had a horn! Needle didn't budge,although something must be working if the horn sounds.

Wondered about combination box, but from what I can gather it has nothing to do with temp gauge. Is that right?

Thinking I must have a bad gauge, I replaced the instrument cluster. Still nothing!

So, I now believe there is a problem in the wiring between the temp sender and the harness that connects to the instrument cluster wiring. I don't really know how to read an electrical schematic so I would appreciate any help. My specific questions:

1) Does the "Y" wire run from the temp sender directly to the second position, right side of the instrument cluster wiring harness? (see schematic) The one directly under the top position with an "X" (unused, I believe). it looks that way in the schematic, but then where and how does it connect to the horn?

2) Does anyone know what "I", "E", and "U" labels on wiring stations on the back of the temp gauge stand for?

3) In testing wires for continuity, would I check between the temp sender end and the harness end connection of the "Y" wire?

4) Do I need to test the "I", "E", and "U" wires? If so, can anyone help me understand where they go? I don't understand the schematic.

View attachment 453844

Thank you for helping me wade through this quagmire!

Key on, at the temp sending unit, you should have voltage on the disconnected yellow wire between your volt meter's red (+) lead while grounding the black voltmeter's (-) negative lead.

No voltage? Then at the instrument cluster and back probe the yellow socket with the red lead while grounding the black lead. You should have voltage.

No voltage? Bad circuit board or bad power passthrough on circuit board.

Voltage found on back probe test? Ohm out looking for resistance or and open on both ends of the yellow wire. Prick the yellow wire progressively moving from one end to the other end until you've found the open or bad part of the wire.

If no voltage is present you heed to check the U pin of the gauge for power and confirm power and ground on the I and E pins.

The U pin is where the gauge sends out a reference voltage signal to the sending unit through the yellow wire.

I and E are power and ground.

 

[KYKub]

Thank you, Eric, for the quick, concise, and detailed response. I'll follow your advice and let you know what happens.

Any idea about where in the circuit the warning horn is, and whether or not that might be an issue?

Thanks again!

 

[KYKub]

I have voltage at the yellow wire connected to the sending unit. Also at the "U" terminal at back of gauge (when key is on). I ran a jumper wire direct from the gauge to the sending unit and the gauge never moved when I ran the tractor. I was in the garage and could only get the engine temp up to about 160 degrees since I wasn't moving or engaging PTO. Could it be that the gauge doesn't begin to register until above 160 degrees?

I tested the sending unit by taking it out and heating it with a flame; the gauge shot up quickly so it seems to work correctly, at least at very high temps.

Maybe the wire going directly from the "U" terminal on the gauge to the sending unit bypasses the crazy warning horn and eliminates a wiring problem somewhere along the way?

I still have an aftermarket temp gauge installed so I think I'll let it rest until spring and then see what happens when I mow and get the temps up around 180.

Thanks again for your help, Eric.