there is no 'junction block' under the cab - there are 3 harness connectors about under the driver, and there is a stop light switch where the pedals go thru the floor, those are the wiring involved in the rear lights along with the main light switch ....
here's the signal installation info, the connector setup is shown on pg 4 and there's a schematic of it at the end ... main switch wiring
shown here ... sounds like you have possible wrong connections or broken wires, the signals should use the same wires as the brake lights to the back and the tail lights are a seperate wire direct from the main switch [via that group of connectors]
Bill
