The I/R (infra-red) switch on Series III FFR 24v vehicles is known for many problems. The best thing to do is bypass it. It has been known to burn out wiring harnesses. The relay also has been known to over-heat and cause other issues. In short, they dropped this system in later years due to its many problems.
With that in mind, how do you bypass it? Actually it is very easy but here is an in-depth explanation of all the parts. One side note, if you do bypass the switch, look at the bright side - you now have a free switch to wire to something else.
The wiring diagram says that there are 6 wires from the 6 way switch. They are Brown/Purple, Red/Yellow, Red, Red/Black, Blue/Black, and Brown/Yellow. The Brown/Yellow goes t the fuse box and is always hot. The Blue/Black goes to the IR switch. The Red/Black goes to the Tail lights (only hot when in correct switch position). The Red goes to the side lamps (only hot when in correct switch position). Red/Yellow goes to convoy lights (only hot when in correct switch position). Brown/Purple goes to the IR relay and is always hot.
For the IR switch, there are 4 wires. They are Blue, Brown, Blue/Black, and Blue/Orange. The Blue goes to the headlamps and has power when the switch is on. The Brown and the Blue/Orange go to the IR Relay. The Blue/Black goes to the 6 way.
To bypass the I/R switch, just disconnect both and join the Blue wire for the I/R to the BLue/Black on the 6-way (you can use a double male connector).
That is all there is to it.