New post and hello. Electrical questions like you have discovered are not always cut and dry. My first guess is. it could be a black wire. Well that's no help.
Help is the road map of the HumV electrical system. To get the "ROAD MAP" look here>
TM9-2320-280-20-3 and TM9-2320-387-24-2 both have full schematics at the end of the manuals. Google them or at the top of this HMMWV forum at TM's TM's are going to be your HumV buddy when the internet goes down LOL Technical Manual, The owners manual you didn't get with the truck.
Without it one would be a bit lost and there's a good chance to go in circles or changing parts willy nilly.
The wire numbers are the little tags attached near the end of the wires. Think street number with a name like 15A light circuit. starter or glow plugs.
The direction I would take (no short cuts and others may have a back road) Start.... 24 volts leaves the the batteries and enters and passes thru the controller box (smart or dumb start systems) For this situation it comes out on body connector pin "F" wire 15A and on to the lighting switch Pin "F" 15B wire. With the drawing one will see it connects to an internal circuit breaker. Not a lot one can do here... BUT the real test is to check for voltage along the way. This circuit is always hot to the lighting switch (factory). SO this will verify power to the switch. With every positive connection there is a negative, so there is a two way street going on with a ground. That's another question.
This light switch, while mechanically a mess of contacts, simply distributes 24 volts to the selected lamp/s selected and the horn. Why the horn in a light switch you ask? The horn is disabled in the 'BLACKOUT" position has to not wake up the bad guys when tippy toeing around and night.
Gota get the map / a voltmeter (compass) and one will see how easy it is to make the connection and never be lost. Hope this helps, Good luck
Now where did I leave my reading glasses, CAMO
