Trying to get the heater working

Very first question is, "do you have" a factory service manual? If not you should get one. We don't have a 74 to download, but there IS a 73, in the bottom end of this thread: http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617

Now, there were SOME wiring changes from 73 to 74, but most of it is the same If you get into the section on heaters / AC there's procedures in there to check the vacuum on the switch, etc and routing diagrams to show how the vacuum / doors work.

In the back of section 8, 73 was a HUGE change in how wiring was drawn. There's an index behind the diagrams to locate connectors Start on page 8-152 and notice the contents there, "connector charts."

Just below that, in the alpha index, find "Air conditioning blower motor, at D-36. Go to D-36. Make sure you are looking at the AC blower, not the heater blower. Notice the circled "CE-20" This means "connector, engine, no 20"

Now go to page 8-164. This is the start of the connector pictorials. Find "CE-20" This is simply a single wire booted plug, dark green. The wire no. on the diagram is C5-14DGN for "Dark GreeN"

Notice this is IN the engine bay, not under the dash