Well I did some stumbling around on the net and there may be some good info for you on the attached hyperlink, with some older partial schematics (2001 F53). They may not be of much help but it might be a start. If you scroll down the link page there is also another link to a 1999 F53.....which may or may not be of value.
No low beams headlights F53 1999 - iRV2 Forums
Odd that you say when the headlight switch is disconnected you still get headlights? A previous owner doing some fixin' perhaps?
Thor Forums
