Gauge box for 1987 Nautique

That sounds like a pretty classic low voltage problem to me.

There's no such thing as a gauge box on an 87. Some of them had alarm modules, but that doesn't even come into play here, and wouldn't help your problem.

You'll want to add a new ground wire from either the battery or the engine block. Then, have that wire go to a bus bar, and tie in all your grounds to that bus bar. Or, if there is a ground bus (or ground strip as it's called in the schematic) already there, just run your new ground wire from your engine to it.

Then, you're going to want to run a new, (in parallel with the original or replacing it) hot feed from either the fused side of the engine breaker, or the battery positive. If you use the battery positive, you'll need to fuse it.

Check out the 87 wiring schematic from our reference section:
http://www.correctcraftfan.com/downloads/1987_dash.pdf

Also, check this thread on re-enforcing wiring, the 93 is a little different layout but the principal is the same:
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=21901&PN=1&title=added-new-dash-ground-to-93-with-pics