Possibilities... I'd be looking for a wiring fault or a fault in the CECU or mismatched programming between the CECU and the instrument cluster node.
if the speedo is also not working it could be a vss problem or an issue with the gear or square shaft where speedometer hooks to tranny/ if speedo works just no overdrive there is a temp sensor on the tranny that can keep od from working or may be wiring issue with factory od on/off switch
Of which low pressure switch are you speaking? Engine oil pressure switch? If you're checking that, remove the oil pressure sending unit and temporarily put in an oil pressure gauge. If you're checking the AC low pressure switch, pull the switch from the AC low pressure line, Jumper the switch socket and see if the AC compressor comes on. If it does, you either have low refrigerant pressure or a bad switch. If you KNOW the pressure is up and everything else works, you have a bad switch.
The brake light switch is not air actuated.
An isolation switch
Isolation switches can be closed with loads connected. The isolation switch should not be opened under load unless the switch is load rated. This information can be found on the isolation switch's cover as to the amount of current that can be safely interrupted.
On the bottom of the transmission with a set of wires going to it from the speedo assembly where the speedo cable is connected for a manual tranny
The in-out isolation is the attenuation between input and output ports of the switch when embedded in a circuit, when the switch control voltage corresponds to the "OFF" state of the output port.
No it will not.
To adjust the pump pressure switch for optimal system performance, locate the switch on the pump and use a screwdriver to adjust the pressure setting. Increase the pressure if the system is not working efficiently, and decrease it if there are issues with overpressure. Test the system after each adjustment to ensure it is functioning properly.
Some bulbs may be burned out, or a blown fuse or the dash light dimmer/brightness control switch is turned off.
To adjust the pressure switch on your water pump for optimal performance and efficiency, locate the switch on the pump and use a screwdriver to adjust the pressure setting. Increase the pressure if the pump is not turning on or off at the desired levels, and decrease the pressure if the pump is cycling too frequently. Test the pump after each adjustment to ensure it is working properly.
check to see if you have enough low side freon pressure and/or if the low pressure switch is working. bypass switch by crossing the wires of the switch with a paperclip to apply trigger voltage to the coil on the compressor,also check to see if there is voltage going to the low pressure switch,if these measures don't work,disconnect the high pressure switch to see if that switch is stuck and shutting off power thru the relay.