I have no lights, wipers, heater fan, radiator fan, horn, or anything else that should work electricly. I've unpluged all the harnesses to the various light systems and, when powered by an independent power system, they all work which eliminated the harnesses as an issue.It would appear to be in the cab somewhere. Everything that is supposed to have power to it with the key off, does. But, when I turn the key on, the bulb check relay clicks and nothing has power. For instance, the head light switch has power to it with the key off, but, when the key is turned on, the bulb check relay clicks and the switch no longer has power. When the key is turned off, the power comes back. Also, with the key off, the head light switch has power to it, but, if I pull the switch on, the same relay clicks and there is no longer power to the switch. When I push it off, the power is restored. The same is true of the rest. This happens with the horn and brake light switches. They have power to them untill they are accuated, and then the power is lost untill they are de-acctuated at which time the power returns. Does anyone have an idea what is going on?