YM135/YM186 Alternator wiring diagram

[bmaverick]

Here's the wiring diagrams for the 3-wire regulator and the 4-wire regulator setup on the YM135. I found this diagram years ago, but haven't seen it on the Internet since...
View attachment 678851

We have this YM135 / YM155 Parts Manual along with the YM155F model schematics at the Yanmar Tractor Owners Group files location. Some of this was posted on the now defunct Yahoo Groups. We've migrated over to GroupsIO. Our goal is to complement the tractor forums on the web and help out where the community can.

 

[bmaverick]

Followup:

I installed the new regulator on the YM186D. Finally everything works as it should. No red light if the engine is running.

This is new. As long as I have owned it the charge light came on randomly as the engine slowed down but the battery voltage tested ok. Then recently the light was on all the time and the battery needed charging.

$20 for a 'take-off' regulator (obviously never mounted) from a Kubota dealer on ebay remedied everything.

I think I mentioned above that there was near-zero resistance between the alternator's two terminals so that wasn't the problem.

Thanks everybody for lots of good advice.

You have me leaning in the same direction too. Just tooooooo cold outside. In 2-1/2 months, I might have it warm enough to look at the issue. Till then, the trickle charger is our friend.

Really glad you have the issue resolved. Nice to just jump in the seat, start and go. :thumbsup:

 

[California]

You have me leaning in the same direction too. Just tooooooo cold outside. In 2-1/2 months, I might have it warm enough to look at the issue.

Tips for replacing the regulator: If you can get one of the old regulator's mounting screws out, measure it and buy replacements before doing this project. Get shorter screws if the new regulator has thinner mounting pads. Assuming you can get the old screws out the whole project should take a couple of minutes.

The Phillips-head screws holding the regulator to the firewall were badly stuck and so soft that the screwdriver just chewed up the slots. I drilled the screw heads, starting with a countersink then two drill sizes. Then lifted off the old regulator, and took out what were now headless studs.

I didn't have matching screws in my junk tray but I had new matching nuts, so I threaded them onto the studs and peened over the drilled stud tips to make 'bolts'. Due to thinner mounting pads on the new regulator the new bolts penetrate the firewall the same depth as before.

Mission accomplished. Good for another 40 years.