These switches are another of the things where "the more I try to learn, the more I realise I don't know".
As far as I can tell, there are six variants of these toggle switches.
In the Ford Spare Parts List Wadeproofed Equipment they are listed as:
C49Q-10999-A, Toggle used for dash lamp, tail lamp, or stop lamp (2 additional switches used on KL welder truck)
C49Q-10999-B, Toggle fuel tank
C49Q-10999-C, Toggle, ignition and instrument
C49Q-10999-D, Toggle, RH Headlamp isolation
C49Q-13239, Toggle, clearance & tail lamps or clearance, tail & headlamps
C49Q-13746, Toggle, no "off" position, tail and stop lamp selector.
Comments:
The ones I have seen are C29Q or C39Q rather than C49Q.
Although several of the switches look similar to each other, they function differently due to the internal components.
10999A and 10999B have three wire sockets on the back (same style socket as shown in Brian's photos).
10999A seems to be SPST with 2 terminals common.
10999B seems to SPDT, no center off position.
10999C, 10999D and 13239 have six locations for sockets in the rear, not all spaces actually have sockets in all styles. When I first noticed the missing sockets on samples I recovered from Chevrolets, I thought the sockets had been ripped out during dis-assembly, I now believe they were not needed and were not installed. Depending on internal design, these units could be anything from 3PST to SPST with multiple common terminals. See also
http://www.mapleleafup.net/forums/sh...t=single+throw for more on the wiring of these switches. Naturally, an ohmmeter would let you determine the connections without opening up the switches. Although the switches aren't very hard to open (or re-assemble), there are a few fiddly bits inside (springs and sliding contacts) to be careful of.
13746 has 4 terminals arranged in a diamond pattern. The two central terminals are common and can be connected to either of the end terminals.
I would also comment that the Chevrolets I found these switches on didn't show particular signs of having been wadeproofed but the Ford parts list referred to shows the 10999A, 10999B, 10999C and 10999D switches as "peculiar to wadeproof vehicles" while the 13239 and 13764 are not designated as peculiar.
Some of the panels had a mix of the 13239 switches with more conventional SPST and SPDT switches - which fits with the above "peculiar" discussion.