If everything that only works when the ignition switch is ON (transmission shift pad, dash HVAC fan, gauges, etc) is not working the likely suspect is the ignition solenoid (more likely), ignition switch or wiring between the two.
Freightliner may be able to help you locate the ignition solenoid.
To test:
Will have two large lugs-- one reading chassis battery voltage all the time. The other should read the same voltage when and only when the ignition switch is on.
There will be either one or two small terminals. If only one, it will be the signal wire from the ignition switch. If two, the other will be ground. If only one, the ground is through the metal body.
If you do not get chassis battery voltage at the "other" large lug when the ignition is on, check for voltage at the small positive signal wire (should have 12 VDC positive). If that is what it has, but the other large lug doesn't have chassis battery voltage, the solenoid is BAD. Tapping on it may work short term.
If no voltage at the small signal wire with the ignition on, remove the small wire and use a jumper wire from the chassis battery large lug to the positive small signal wire. Small wire is fine-- it takes less than one amp to close the relay.
Emergency work around: Label all the wires on one large lug. Remove then and ADD them to the other large lug. All you have done is manually done what the ignition switch and solenoid do for you. Be sure to return wires to original position when you stop.
