this post will be if you have an 87 to 91 truck and want to fit OBS heater control panel in. for reference I used parts from a 97 f250 diesel with factory A/C. the truck that the parts are being swapped into is a 91 f350 diesel with factory A/C. I will do my best with pictures and directions to help anyone successfully perform this swap. the first thing you will need are the parts from a OBS truck. such as, - control panel - blend door cables - black 4 wire square plug for the blower motor speed. you don't need the wires, they will be swapped over. - small 2 wire plug for the lights. you will need to cut the wires for this plug and reconnect them to the truck. - vacuum hoses. you will need the rubber plug that goes to the controls. you will latter separate that piece from the plastic connector. - you will need some tools but I think it will be all pretty self explanatory. this is what the end result will look like. I will be editing this tread with pictures and details.