I've done more than I can remember.
Vertically on one end of the truck.
Super glue, silicone, or hot glue.
Just try to get the main body and not the top and bottom plates.
I use the round ones that come with Phoenix, sometimes grind a small flat on one side.
Wires will go though the same hole as motor/power leads if you put them on that end.
Just leave lots of extra inside so you can pull the truck down for maintenance.
I've seen folks put them inside the fuel tank, but that only works on straight track.
No experience with diesels, but I always mount mine under the trucks, horizontally. That puts the reed switch down where they should be (just over the top of the rail) and out of sight. This usually requires some sort of minor mounting bracket made of styrene or wood. Then I glue the reed switch to that.
We have mounted all of our small glass reeds on USA and Aristo recessed in the fuel tank. We used a Dremal and grooved out a slot in the fuel tank for them to set in, then put vinyl tape over them and painted.
Like Curmudgeon said.. Glass reed will get busted if now protected. We found out the hard way and had to change them out and now we recess them.
Reason for installing them on the fuel tanks is that we use both outside of the rails with a small mag and one in the center of the rails.. This give us the key for the Bells & Horn on outside of tracks.
The Dynamic brake is the center reed. This works great when going down hill and drifting.
Our Steam Eng. have Reeds set up on end. (They look like ADT door enclosed package SW.reeds.) We mount them on the tender trucks, between the wheels..
Anyway just an idea.. We don't like to have anything showing so that's why we recess them in the tanks to give them protection when derailing ..
"Course we never derail .... We're just not use to all of the hp . and wheels jump up off of the tracks with all of the torque with touchy heavy hand throttle. " ya right. laf.