JD 850 electrical trouble shooting

[Niji]

Hey fellas,

I'm grinding through troubleshooting an electrical problem with my mid-1980s JD850 (made by Yanmar 3 cyl diesel--4 wheel drive model).

It has stopped charging the battery--also the three dash indicator lights no longer burn when the key is turned on. Fuel guage, however, fires up when the key is on. I have removed and cleaned up the terminals on the ignition switch--it seems solid, and that did not fix it. I have the old school voltage ragulator; I have checked it per the diagram and instructions provided here: https://www.tractorbynet.com/forums...identifying-electrical-part-850-regulator-jpg

It checks out, although it does state on those directions that if the test runs okay, the VR still may be bad, but if the test does not come out clean then the VR is defitiely bad--so not conlusive that the VR is indeed good.

I have 12v+ to the field post on the Alternator, and I even used a jumper to excited the field manually to be sure, and still nada for charging.

No bearing noise or other apparent issues with the alternator.

Tractor cranks and runs fine--I have been limping along by charging the battery, jumping it with a truck, which gives me a start or two worth of juice, then rinse and repeat.

I would think brushes or some other alternator issue at this point except that the dash lights deal is making me think ignition problem, not alternator. Does anyone have details on checking the ignition swtich with an ohm meter to see if it is working for sure? I doubt it is the problem, but just want to cover all the easy bases first. Since there is an Ignition aspect to the Voltage Regulator, I still suspect it. My next thought is to pull that and pop the top for a look. If there's a way to avoid replacing it with a $70 solid state unit, I'm all for it.

So here's the symptoms in a nutshell which I hope may trigger an obvious problem y'all might know of for sure:

-alternator not charging
-cranking and starting fine when jumped
-not illuminting the three dash lights when key is in on position, or glow plug indicator light when key turned backwards for glow plug engagement
-alternator field wire does have 12v+
-Voltage Regulator checks out okay per the ohm meter test (see link above)
-All fuses are fine
-I have been steadily cleaning every connection I come to

I think that about covers it. Any insights are much appreciated!

Thanks!

 

[WranglerX]

I would look for loose or dirty connector or a blown fuse.....IF you have wiring diagram and the time a trouble/test lamp can be very informative....

I have 4 different meters, two analog and two digital, and I usually grab this first....

Alligator clip to ground (chassis) and probe to circuit, lamp lights you have power (12 Volts ?) lamp doesn't light 12 volts missing or you are on ground wire...

Part of alternator problem maybe lack of 12 volts to trigger the initialisation of charge cycle caused by missing voltage on other instrumentation.... Some vehicle get initialization through voltages from ALT indicator lamp... Anyway just a thought...

Dale

 

[Niji]

I've been poking and prodding for a couple of days--took the old school Voltage Regulator off and went through it. I took some fine grain sandpaper to the relay contacts and made sure everything was moving in there. I went through everything again this afternoon, hooked the VR back up and it started charging. My best guess is it was crusty contacts inside the VR, but I cleaned up other connectors, so I can't rule one of them out. The dash lights still don't come on when the key is turned on--so that must be a separate issue. Going to go check those now--the service manual says temp and oil press lights can be checked by taking their wires loose and going to ground with them--should light their lamps.

Anyway...it's alive! Alive!