MT 372 dummy lights

[Ilikeurtractor]

Which one has the .5 ohms? The field or lamp coil?

 

[shags-72]

I am not sure so here is a picture and readings i get and from where I took them.

 

[Ilikeurtractor]

Something doesn't appear right on the wiring diagram in the manual page I uploaded now that you got me looking at it. The lamp relay should have a resistance around 22 ohms. The field relay will show near zero ohms until you open the lamp relay manually since it is normally going through to ground and this is where one side of the field coil attaches. Once the lamp relay switches the field relay will read 90-100 ohms, at least on the two I tested. Check that and see what you get. If I get a chance I'll draw up a new schematic based on the regulators I have. There is a resistor on the back side of the regulator that is around 10 ohms. I'm not sure where I got the 35 ohms in the diagram but I bet it was likely to represent the field coil value at the time I wrote it but that doesn't match what I'm getting now. Again, I only visit this when I have problems and I have no idea if there are multiple versions of the regulators used floating around.

 

[Ilikeurtractor]

Here is what I got using the regulator I have handy. I'm not going to guarantee the accuracy of my schematic but I'd say it's as least as good as the one in the manual :laughing: I made the assumption the plug wires are labeled correctly in the manual - is this too much to assume????

 

[shags-72]

Well I am not sure if I am testing the right things but I am getting those readings on mine too. .5 and then make the contact and around 100. I checked the resistor and it was around 10. the other coil is 23. Crazy man. I chased the wires to define the field coil and looks like I have it but I am just a hack so not really sure. I took some pics of what and how I am testing to be sure I am on the right path.

field coil test is 100 with contact closed by finger


light coil test is 23 and no difference with either contactor manipulation



Once again, thanks a million for helping me out.

 

[Ilikeurtractor]

Isn't this fun??? You're doing it right. Wait until you get to testing the solid state ones It will make the mechanicals look like child's play. The light solenoid coil is not affected by the position of the solenoids so it will stay at 23 ohms. It's starting to look like your regulator is ok. If your voltage goes to 18V that probably means your field solenoid coil is not getting energized for whatever reason but the problem is outside of the regulator. The fact your charge light comes on when the switch is off is very strange. It could be the switch or a short somewhere. Is the charge light on when the key is on? Both when the engine is running and not? You're welcome for the help, but I haven't really helped you yet as you still have a broken tractor Actually you've helped me (and others) by uncovering a problem in the schematic. All this time spent now will potentially save me, you, or someone else a lot of frustration in the future.

 

[shags-72]

well I guess I will have a spare regulator. :laughing: The light would come on when the key got turned on and went off when the engine started. It did come back on when the key was turned to off with the engine running. Could it be a burnt contact? Doesn't really look like it. I know the connectors at the alternator and the regulator don't look good. I could check the wires for a break I guess. I know it is boiling the battery if I leave the key on when it is running and lugs the engine horribly. So what would keep that from being energized?

 

[Ilikeurtractor]

I've had problems with the connectors too. They get brittle and break over time and can cause shorts and opens in the circuits. New replacements are out there. Since we've checked some things on the regulator and that isn't yielding an obvious cause let's go back to the charge light. We know that shouldn't be on when the key is off. How about the horn - does it operate when the key is off? I'm trying to understand why the charge light has power when the key is off and the horn, water temp, and oil lights are connected to the the same terminal that normally supplies +V to the light. What two wires did you work on going back to your first post?

 

[shags-72]

I will have to look at the harness when I get home.

 

[shags-72]

I've had problems with the connectors too. They get brittle and break over time and can cause shorts and opens in the circuits. New replacements are out there. Since we've checked some things on the regulator and that isn't yielding an obvious cause let's go back to the charge light. We know that shouldn't be on when the key is off. How about the horn - does it operate when the key is off? I'm trying to understand why the charge light has power when the key is off and the horn, water temp, and oil lights are connected to the the same terminal that normally supplies +V to the light. What two wires did you work on going back to your first post?

I replaced the female connector on the white/red stripe wire on the alternator connector, which looks to be the A connection according to the wiring diagram in my manual, and the female connector on the white wire on the regulator connector which looks to be the N connection on both alternator and regulator again to my original MT 372 manual I attached. I don't have a horn. The oil light just comes on as normal when the key is on and the engine not running.