Re: no overtemp light
Going to bet you don't. I had a '89 tower and I don't think it had one.
It's not rocket science. It's just a single pole single throw snap action switch that is activated by heat (like a frog clicker you probably played with as a kid, but activated by heat, not thumb pressure).
Come off your accessory connection on your ignition switch (12V as long as engine is receiving 12v) to a 12v lamp of your choosing. On the other side of the lamp run a wire to the temp switch. You should be able to order one from your local Merc dealer. Mine is set for 195F which is a good number.....'02 90 hp.
The switch only has one (brown) wire so you will have to get ground somewhere. I'm not explicitly familiar with the switch if you were holding it in your hand and looking at it (never had mine out and I'm in the house and it's in the garage), but in normal service (factory installation) the outer case ties to the engine block via the water jacket cover) and that is where the ground is made for the light if your engine overheats and the switch closes.
The switch is held, has to be held, in place with a screw (or two) which should go through a hole in the outer shell of the switch. Put a screw/nut thru this hole and put a lugged wire on it to make your ground. Run the other end of the wire to the engine block (ground) somewhere where it's clean and shiny (for a good connection).
The top, rear of #1 cylinder should be the hottest place to be concerned about overheating so that's where I 'd mount it if I were doing it. I would put it on the block, as far aft as it would go just infront of the flange that the water jacket cover attaches to.
I know steel isn't the best conductor of heat, but it should be good enough for what you want so I'd get some JB Weld (2 part epoxy with steel shavings suspended in it) and glue her to the block. If you can find an aluminum impregnated epoxy even better.
No reason why that wouldn't work for you and although it isn't in the water, it's close enough and alum is a great heat conductor so you probably wouldn't be 5-10 degrees off from a factory installation and that's surely a whole lot better than not having one. I lost an engine once because of a stuck stat and no bypass and no alarm.
Mark
