I noticed today that I have hot exhaust steam coming into the engine compartment from where the wires for the stern light pass through the hole in the transom. It had condensed on the flame arrestor, distributor, and wires. anyone ever see any thing like this before. wondering if impeller is going bad and water exiting into the silent thunder platform is way to hot from lack of flow. temp guage read 150 degrees though.

The hole for the stern light is on the top of the transom between the sun pad and the swim platform, correct? I wouldn't think that could even be possible, is it coming through the hole for the ski eye as well? I'd be looking at the exhaust hose to thru hull connection.
If it's not coming from there then check your donut gaskets sandwiched between the outside of the transom and the swim platform. The gaskets are known to go bad and leak from age but it will leak out the top between the outside of the transom and the swim platform.

On my boat the tailpipes had loosened up and were leaking exhaust into the engine compartment. I never ran with the drain plugs in the platform but if you are perhaps the water is leaking in through the area around the tips? The platform has to be removed to fix this. I through bolted mine when I had it apart and resealed the tips.

My light is 2 inches round on the platform. If you remove it, you can see through it into the engine compartment. You can also put you fnger in there and feel the gasket running a 1/2 inch above it. I ran it on the hose and saw some steam entering from there. Also how hot are the exhaust maniflds and risers supposed to get? Can you place your hand on them?