Are MTH Diesel shells exchangeable with the same shells in any year?

I would say as a universal comment, no.  I'm sure some (many?) are, but I have seen those that are not.

Thanks, as always, GRJ,  I appreciate your expert input.

The screw holes will likely line up. However, electrical connections are a completely different matter, especially if you are considering early production vs late production shells. MTH changed the wiring quite a bit.

Chris

LVHR

I have two experiences with this.

First is a PS1 premier GG-1 versus a PS2 premier GG-1.  The fit was perfect with the exception that the center screw holes did not line up unless I flipped the shell around.  Then all fit perfectly, but the F was in the wrong position so the engine started in reverse and the electro couplers were backwards.  Had to swap some wires to get it all right.

Next was a premier dummy GP35 vs a premier powered PS2 GP35.  Shell was similar but not perfect.  The headlights were actually different too. Screw holes lined up, but I had a tough time getting it on over the electronics as lehighline explained.

It can be done.  Just don't expect it to be perfect and easy.  Then you won't get aggravated if you have to do a little extra work.

Have Fun.

Ron

Another thing would be PS 1 and 2 shells had incandescent light bulbs whereas PS 3 has LED and will not swap out without electrical modifications.

The wiring not only being different, but the ones with spring pads for connections to the frame frequently change position or number, and even don't have them at all.  OTOH, you could get lucky if you stick with the same vintage electronics and have a drop-in replacement.

Great info here.  Thanks guys!  I was going to bid on a few on EBay but I passed.  You all helped me save money and potential frustration or failure.  I did not consider the wiring being different, and leds, etc.  Interesting...  because otherwise the shells look aesthetically identical on the exterior.  I was hoping any age PS2 engine shell would be able to exchange with another road name PS2 but the years between early  ones and later ones could be significant and I was thinking PS3 would work with them, too--but likely not.  Plus the early PS2 even uses a different battery (bcru)  than later PS2 -- and that could mean different systems.  Your experiences stated here solves those questions.