Okay to start from the begining. In 08-09ish my heater core went bad, i have AC and as much fun as it is to take the box apart i got a new blower motor as well. In 09 i put the supercab on, used everything out of my single cab. Worked great (well as great as a 79 heater is) until last December. Started cutting out. Fan on high, it sounded and only moved air as if it was on low. Sometimes it wouldnt work at all. I replaced the switch, no change. I checked wires, nothing.

So today, its getting cold again. I have the air box split getting ready to take it out and see what i can see. I guess im just wondering if anyone else has had a similar problem and what the cure was. As of right now i have no fan... at all.

If someone has a wirin diagram for this that they could link, i would be more than grateful. There is a round female terminal on the engine side of the firewall that when unhooked means i get no juice to the blower motor, im not sure, but i dont think thats where it should get power from.

I know the subject has come up in the past, but has anyone found anything that actually works to make our heaters actually move some air? Going through all the trouble to fix this thing right, might as well make it so it will get warm inside not just "not cold".

If this doesnt work. I think i may look into swapping in a whole new air box out of something like a 2000 F-150 or similar. If possible i would like to add vents to the back seat area, just something like floor heat that goes under the front seat to get the back of the cab warm. EIther that or vents throught the roof liner like econolines and suburbans. Whichever way, i need a better than average heater, tired of getting where im going before it gets over 50* in the cab.

 

That terminal on the engine side is the correct one. If its the one in the top left of this picture with blue tape:





I had problems with that thing too. Try cleaning the terminals with some emery paper and packing that terminal full of dielectric grease. See if jiggling it, having it in the middle or towards one end of the connector makes it better. Just a WAG but I think the reason it gets power from the engine side is because if it came in from the front of the box they'd have to have a funky connector so it wouldn't get caught up in the squirrel cage.

As far as the mehhhhh heater, when you replaced the heater core did you replace the surrounding foam? I didn't at first and my heater sucked, check this thread... https://www.ford-trucks.com/forums/1...r-problem.html

 

Thanks for the speedy and excellent reply. That is in fact the wire. And best i can find its dead. The other terminal there, what does it do? I touched the black w/yel wire to it and heater kicked on, then i think i blew the fuse to that wire. So i wired the wire to the battery.... WOW, thought i had a hurricane in my dash, blew all sorts of dust and crud out of the defroster, i can say it has never blown like that. It also was high only, so i must have been bypassing the switch and resistor.

I have 4 wires coming out of my air box. Ground- grounded, black with yellow (no longer has that connection, it has a different one spliced in) connected to the correct blk/yel wire (dead). a black?- apparently goes to AC pump, and a female plug with a male spade inside it cant remember the color, but is not hooked up and hasnt been hooked up ever that i can tell. Also, the harness on the firewall has a round female 2 hole plug that is not used either. Ill take some pics, but i cant remember how to get pics from my phone to the internet.

 

Ok heres the pics, hope you can see them.

The blower motor power wire- blk/yel Plug on the left side is grn/red i think, same you have, electric choke maybe?


The plug coming out of the air box assem. - gry/wht


And the plug more towards the center i was talking about, has a brown wire in it, so i wonder if its under hood light, or an accessory light.

 

I guess at the risk of sounding lazy, any tips on where to start looking for the lack of voltage in the blower motor power wire (blk/yel) ?

 

By the other, do you mean the green one coming out of that harness or the black coming off the blower motor? I'm not near my truck right now, but according to my '78 diagram, if that green wire has a white stripe, its for the A/C evap. thermostat. I have no A/C, so that's why its not plugged into anything.

If you connected the BLK/YEL wire directly to battery, you were in fact bypassing the resistor and switch. When you have the BLK/YEL connected to the non-ground wire (orange in my case, idk if that's a splice or not), it is hooked up to the switch. Hook up a voltmeter and see if you have a different voltage drop for low/med/hi. If not, then it could be a number of things, short to ground, bad switch (which you replaced), or bad resistor connections (connections because high bypasses the resistor coils, if it were just the resistors high would work and the others wouldn't)

 

Arrgh ya beat me to it ya scurvy dog...

Pics didn't work

I have a manual choke, so could very well be.

Which brown wire are you talking about? The one hanging by the valve cover? My dad ran to get some sheetrock with my truck, he should be back soon and I should be able to look.

Try the pics again, I'm not sure which gry/wht you're referring to.

Hahaha, I'm lazy sometimes too. Look to see if it's shorting out where it comes through the firewall. Insulator rubbing on bare sharp metal edge for 30+ years = short. Otherwise check for voltage drops back at the splice by the resistor and the connector after the switch.

 

Pics are uploaded to and linked via my album so im not sure why theyre not working for you, i can see them when im on the thread.
Brown wire is in a 2 wire round rubber type plug above the right valve cover, i dont think its related to this mess, but wondered what it was.

I have 4 wires coming out of the air box: 1 Blk/yel- motor power, 2 black ground, 3 black/wht? goes to AC, 4 grey/wht goes to??? plug is a female with a male spade in it. Its been unhooked and has had leafcutter bees working on it since i seen the truck 4 years ago.

 

Hmmm, not seeing any pictures anywhere...

I'm guessing electric choke or CA emissions sheat.

Those wires you're talking about, they don't match my '78 shop manual info or my '79 haynes manual.

Time for the old fashioned way. What happens when you jump the switch on high to the blk/yel wire after the resistor? Only do it for a couple seconds, don't wanna blow the motor there. This is ruling out any problems with the circuit after the resistor. Just to make sure you know, because I didn't know this till I had it apart, the plug into the air box actually has the resistors directly on the other side inside the plenum.

 

Not seeing any pics here and only two in your gallery?

 

Wondering if i fixed the pic problem...

On the other hand i made the pickup problem alot worse... not sure exactly what i did do, but i dont have my radio or dome light now. Only thing inside i can verify that is working is the fuel gauge.

 

None of the fuses or fuseable links are blown that i found. The green wire in the plug next to the fan power plug is green with YELLOW not red i found. When i jumped the fan to it and burnt it out i wonder if thats what took out my my power to everything else.... now find out where and how its burned out and what is causing it. Oh blinkers still work when the key is on.

 

Now i remember why i was putting this off... see me and wiring have a mutual, hate-hate, relationship....

 

Do your hazards work?

Yeah, direct battery power may have not been good. Me...multimeter...blower motor...87 grand am... been there done that haha.

According to my haynes, I know why you don't have a dome light. GRN/YEL goes to the door switches.

Tracking down the radio now...

 

Where are you getting switched 12V to your radio? What color is the wire?