Starter lockout switch
 

1984 300D, was having trouble with starter not engaging at times in park, works okay in neutral, checked adjustment procedure in the transmission manual, check pin does not line up with detent in housing. Manual says loosen the two switch mounting bolts, at this point the manual doesn't say how to make the check hole to line up, with the mounting bolts loose, are you supposed to be able to slide the switch housing to make the holes line up?
Thanks
Jerry

switch might be bad

sometimes worn shift bushing can cause this as well

I had the same issue on my '79 300d

replaced the switch, all is good

bonus...now my reverse lights are working as well...

Also known as the neutral safety switch.

The white plastic ring needs to be rotated to remove the electrical connector. I can't remember what locks it in place.

While you down there you may also need to change the linkage bushing which are cheap to replace. With the red sort of circle.

There is some sort of alinement you have to do when installing it, but I cannot remember the details.

Ichanged all the bushings about a yead ago, I recall I didn't adjust the switch to the shift linkage until the car started not starting in Park without jiggling the shift lever. The book says to put a 4mm pin in the black plastic hole in the split of the lever on the side of the transmission and that the pin should mate with a hole in the switch housing. If it doesn't, loosen the two mounting bolts and I guess move the housing until the pin lines up. My question is , is this correct, don't want to start jacking the switch housing around and screw something as, y'all know, there isn't much room to work under there.

For the alinement pin.

If you have an industrial hardware store you can buy a single 4mm drill bit.

Some cheapie tool stores have like small set of metric bits with 4mm in them. Often, they are only suitable for wood working but they can supply the size for an alinement pin.