I am assuming that the 1083 has a relay for the horn because the size of the wire I don't think would support 12vdc or 24vdc very far on distance. There is no relay on the board for horn. I was using the 1078 schematic for reference and mode of thinking and since that is not pertinent to the 1083 I really am just running on assumptions.There is a flasher module behind the passenger kick panel. There should be a breaker for each circuit on the board though. That is the only breaker panel on the truck. There are 2 large relays on the underside but if your truck starts then they are working. Do you have a panel cover there is a diagram showing what relay/breaker does what.
The two large relays you mention earlier you said were on the underside, underside of what?