Your engine has two high-temp switches. They are not a temp sender, but two on/off switches. Each head has a switch. The switch is under the head cover and nests in the head. To access, you only need to pull the head cover-not the whole head. The wire that goes into the head is brown. Both wires connect to the horn in the control box. When a (or both) cyl heads hit 212 degrees, the switch goes to ground. That ground goes all the way back to the horn and sounds the horn. Once the cyl head cools back down to 175, the horn quits. That 175 is still way to hot. Normal operating temps for both heads is between 143 and 155 at idle in a warm lake. Once the engine gets up on plane, there is extra cooling and the cyl head temps could go down maybe 20 degrees. This is normal. If you have a laser temp gun, you can easily check the engine temps. Oh, another thing, with those heads and the compression, I'd be running premium fuel. I do on my high compression crossflows.
The 76 200 Johnson/Evinrude engines were a really unique engine. They had tons of low end grunt but did not breathe well at top end. Also, the very early 1976 production engines had very high compression heads. The were so high in compression that they had warranty problems early on. The factory took all the heads and ground them so that they did not make as much compression. Kept the original part number. 
Few of these "good" heads still exist. Here is a picture of one of the early (good) heads. If you ever pull a head off your engine, compare it to the one in the first picture. The second picture is a factory head which had some of the pillow machined away to reduce compression.
