I don't see an electrical schematic diagram available on WHALER.COM for the 2000 DAUNTLESS 16. Here is a diagram for a later model, c.2010, which might be useful as a guide:
http://bostonwhaler.com.s3.amazonaws.com/resources/180-Dauntless-Wiring-Diagram-and-Parts-List-2010.pdfIf a circuit appears to have no power, the first element of the circuit to check is any sort of current protection device, like a fuse or circuit breaker. You mention you see 12-Volts at the switch, so that should indicate the fuse or circuit breaker is in a normal state.
Generally Boston Whaler wiring insulation colors follow the color coding scheme described in an article in the REFERENCE section. See
Marine Wiring Color Codeshttp://continuouswave.com/whaler/reference/wireColorCode.html#BWThe wire colors for the positive circuit are as you surmised: gray for the combined sidelight lamp, and gray-with-white for the white-all-round lamp.
Generally the positive circuit feeding the lamps passes through a switch so the lamps can be controlled. The negative circuit of the lamps generally is wired to the the negative power distribution bus at the helm area.
B.E.Coyote wrote:Is there a ground connection that the [combined sidelight lamp] and [white all-round] lamp share that is not at the dash panel switch?
The negative circuit should be on conductors with black insulation. Note that in a typical wiring arrangement the black negative conductors from the lamps will NOT run anywhere near the switch that controls them. If there is a black conductor at the switch, that conductor is probably part of the LAMP GROUND circuit of the switch if an illuminated switch.
It is often seen that Boston Whaler will use a paired flat cable with gray and black conductors (often called zip cord) for wiring of the navigation lamps.
When you attempt to make a measurement of voltage at the lamp sockets, connect your voltmeter positive lead to the GRAY or GRAY-WHITE conductor, but connect the [negative] lead of the voltmeter with an extension cable back to the secondary power distribution panel bus. If that measurement shows NO power at the lamp, there is an open in the positive circuit. If that measurement shows power at the lamp sockets, then re-check with the voltmeter negative on the socket. If that measurement shows no power, there is an open in the negative circuit somewhere.
There is a schematic diagram that shows the typical navigation lamp wiring in older models of Boston Whaler boats at
Navigation Lamp Wiringhttp://continuouswave.com/whaler/reference/navLightSwitch.html