I would first check to see if the lockout switch is there, but not hooked up (See attached picture for the location-It's a D-type OD, but I think they are all in the same place). There might be a plug (which I never seen before) there too.



If not, you will need to remove the transmission cover. I would pull the transmission to do it. You need to check to make sure that everything is correct like the gasket is on right-> best when you have it on the bench. Also, make sure you use a fiber gasket, and not cork one!

I added a switch to a M40 transmission cover because I used a '75 M41 with the remote shifter, I think I either have a bad switch (it was a used one) or I didn't screw it down enough. Sometimes when I'm travelling down the highway in OD and hit a bump, the transmission comes out of OD (I'm using a '81 240 OD relay, so it shifts to 4th gear). So, I'm going to have to replace the lockout switch with a new one I have.

Paul