Ok guys I was in the process of switching bodies on my 76 when I realized the 71 body mounts are crap along with the floor. So now my plan is to rework my 76 body some and just use the 71 box. Anyway my question is my heater switch quit working a while back. I am not very good with the electrical part on these trucks and did not know where to start. I don't use it much so I hot wired the fan motor to a switch and had high speed anyway but I want to fix it right now that I have it in the shop doing other work on it. Is there a resistor or something I need to change? I really don't know and need advice.

My other question is the heater motor is almost gone completely out(makes horrible noise when on) and I was wondering if I can switch the whole box assembly under the dash. I would like to get rid of the ac box on the firewall too. I have the box assembly from the 71 and wanted to use it. I think I'd have to plug a whole in the firewall where the ac box was.
Any help greatly appreciated. Thanks

 

Well as far a plugging a hole, yes if you take out the a/c box you will have a BIG hole where the evaporator was.

No big deal can patch it pretty easy, especially if you have a patch panel cut out of the other truck firewall. That area is where you will bolt you blower fan and run your heater lines thru.

Sorry no help on the heater switch, hang in there I am sure some electrical wizard will chime in.

 

You can replace just the fan switch on the dash. Take the instrument bezell off and take out the heater control unit. The switch has a couple screws to remove & just plugs in. Take it with you to parts store cause there's different ones for different years. Found that out when I did my cab swap. The blower motor might need tightened up. Mine was making noise too til I remembered I didnt snug it up. Its like the blades on the squirle cage was hitting the housing. Hope this helps. Im no electrical genious either.

 

The heater box... 1967-1972 years, will not work with 1973-1979.

You need to get the right one for the right cab.

 

Thanks for the advice. Just bumping to see if someone can help with the switch problem. You say the heater box won't work, not even with a little modifying? How about a f150 box? Are they the same as the 250?

 

Not even with a little modifying. They are too different. With major mods, anything is possible. Not worth the effort, IMO.

Yes, those will work as long as it's 1973-1979. Remember that Factory A/C and Dealer installed or non A/C used different heater boxes, as well as High Output heaters.

 

thanks very much. might be getting a 77 150 soon so that is why I asked. (parts truck)

 

Today I took the complete heater assembly out of the 77 donor and put it in my 76. I took the AC box out from under the hood of my 76, cut a section of the firewall out of another 76 2wd donor I have and welded it in place. I had to use everything; defrost, heater box assembly, switch from dash, so on and so forth from the 77. I tore out a crap load of stuff from the ac setup out of my truck. All I had to do to mount the box was drill one hole for the furthest drivers side stud to go through. I hooked it all up and nothing worked. I then had to dig into the wiring and believe there is a resistor for the ac the way it was hooked. That somehow ran in the switch and I think that was burned out. Of course the donor truck didn't have one so I had to study the wiring diagram I have and just had to switch a couple wires by the switch. The big orange was hooked to a double red/black wire and run towards this resistor. I hooked it just like the donor and went straight to the fuse box with it. All I had to do was unplug the orange wire and plug it in to the existing wire running to the fuse box. After that I have everything working!!!! Had a good day working.

 

Yes, there are minor wiring differences between a/c and standard heater.

Mostly to add a safety accessory relay to run the fan blower, and a/c directly from the battery.

I could go into more detail, however it sounds like you bypassed it the way you were supposed to.

Glad you got it working.