From what I remember, I could barely see if the lights were on during the day when my gauges were brand new. How do your's look at night? It's a relatively low intensity amber light. You sure you aren't chasing a ghost?
Look at the ground wires for the gauges to make sure they are clean and tight. If memory serves, the grounds for the speed should run to the tach which will run to the key switch, which connects to the 10-pin main engine harness...or something like that.
Also, are those your only gauges? If so, your problem may be in the running lights circuit (that's what they should be wired to). Are your running lights working OK? Get access to the back of your switch panel and look for loose wires running from the gauges to the running lights switch and/or breaker, corroded connections, etc. Probably wouldn't hurt to reterminate those wires anyway just to be sure.
I used to have wiring diagrams for those gauges but gave them to the new owner of the boat. Hope that helps.
