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.

 

[Ilikeurtractor]

I'm not a 100% sure on this (maybe 90%?) but it looks like you swapped the A and N wires on the alternator plug during your repairs. Swap those back and I think you'll be in business. I should have zeroed in on what has changed the first time around. For some reason I was drawn to the regulator. If something was fine before a "repair" then breaks, it almost always is associated with what was done and I missed the obvious.

Anyway, the A wire is supposed to be battery voltage and the N is about half of that when the engine is running and essentially at ground value when the engine is off. So if N is feeding the field solenoid coil (because A is energizing the light coil) in the regulator it will not pull in and reduce the field to the alternator by causing its current to go through the resistor which causes the alternator go to full voltage potential and that is the 18V you're seeing. When you turn the key off, A is still supplying voltage to the light solenoid keeping it in a pulled-in state. After that though I can't explain why your charge light is on when the key is off. I measure around 1.5V off the N line on a working circuit when the key is off (engine on,) but that doesn't seem like it would be enough to power the light. Plus, I don't see a good ground (unless the acc line in the switch goes to ground when off) going back through the light.

It's up to you whether or not you want to switch the wires back. Check them against the plug diagram attached and see what you get before swapping. Remember the plug end will be mirrored from the diagram on the attached page (A will be on the right side of the plug and N on the left looking directly into the plug)

 

[shags-72]

I don't think that is possible as I only had one wire out of the connector. Pulled the female spade out, attached the new one to the wire and shoved it back in. That goes for both. I looked at the wires connectors and the alternator. The A is definitely connected straight to the battery as it has 12+v just sitting there. Now according to the diagram it should be a white/red wire and it is. I will admit that this is the wire I fixed. I did trace it and it does go into a yellow wire as it should but when I check resistance in it that wire it goes into both coils. And holy crap it sounds when touching the body of the regulator. Not supposed to do that is it?

 

[Ilikeurtractor]

Ok so the wires shouldn't be crossed at the plug but we're getting somewhere. I'm thinking no on your question. Unplug your regulator and check for continuity on the A terminal to ground (use the regulator body for ground in this instance) in the regulator plug. It should be open/no alarm. If that checks ok, then I would take the + terminal off your battery and check the tractor side plug of the regulator A line to ground for continuity. Use the "-" terminal of the battery in this case for ground. It should be open also. If it's not, unplug your alternator plug and test it again. As a last check while your alternator and regulator plugs are disconnected, check the continuity between the A and N lines at either the alternator or regulator plugs on the tractor side. They should be open also. We've got to be getting close!

 

[shags-72]

Ok according to my diagram the IG (black) goes to body with .5 ohm and the A (yellow) wire goes to body with 23 ohms. I did this from connector to the regulator body. These are with the regulator off of the tractor and only testing the regulator wiring.

 

[Ilikeurtractor]

"A" should not show 23 ohms to the ground/body. It is going through the light solenoid and the light solenoid should only be supplied by the N wire. What reading do you get checking continuity between A and N on the regulator plug on the regulator?

 

[shags-72]

I show open between the A and N. But if I close the coil it show 100+ ohms.

 

[Ilikeurtractor]

What is the value of N to ground?

 

[shags-72]

I am checking the white wire which in my diagram is N and it shows no continuity, but if I close the coil again it is 100+.

 

[Ilikeurtractor]

A and N are swapped at the regulator apparently. I don't know how or why but that seems to be the problem. So a new regulator will fix your problem but swapping those should make your old one functional. How long have you owned the tractor? What were the symptoms that caused you to replace the connectors? When was the last time it was working correctly?

 

[shags-72]

the wires were broken at the connectors and this is the first I have noticed the problem with the lights and charging. I will give this a try tonight when I get home from work. Is there an easy way to get the female spade out of the plug? I had a hard time with this on the one I replaced.