1977 F250 4x4 Ranger XLT.

My blower motor never turns off. Looking at the wiring diagram there is low, med, high but no off, also the switch says low to high. The only "OFF" on the panel is through the vent selector.

So my question is; Does the vacuum switch somehow turn off the blower or does the blower switch?

Thanks

 

I believe the way it works is the blower switch controls the speed of the blower.
There's an electrical switch mounted on the lower vacuum switch that turns the blower on/off through a relay mounted behind the glove box.

 

The blower switch only goes to low, but if you slide the selector switch to Off it will kill the blower motor also.

 

What Mike said. If yours never shuts off even with the vent selector, make sure somebody hasn't bypassed the relay with a jumper wire. While searching the wrecking yards for a replacement relay, literally every truck I checked was missing the relay and had a jumper installed. Not sure how they kept the battery from dying. I think they were pulling the jumper when the truck was off.

 

Guess I need to track that relay down, I cant find it in any of the wire diagrams I have

 

It should be under the dash on the passenger side. It is plainly visible on the edge, not deep underneath. The relay is only on factory AC models, but then I think the vacuum switch portion of the vent selector is as well, so I was assuming you have AC?

 

Do I need to remove the glove box or can I get to it from under the dash. Yes Factory AC. Lastly is it a normal SPST/SPDT relay?

 

If it's the original, it buried up behind the glove box. If it's been replaced (common, these went bad fairly often) it could be in a more accessible location.
If you have the factory wiring diagrams, Ford calls it an "accessory safety relay" and it's shown in the schematics, location 3E.

 

D2LY-14512-A .. Relay Assy. / Marked: D2LB-14C690-AA or D5AB-14C690-BA or CA / Obsolete

1975/79 F100/350 with factory installed integral A/C / 1975/76 F250 Camper Special & 1977 F250/350 Camper Special before serial number O00,001.

Misc. 1972/79 FoMoCo two door Passenger Cars with automatic seat back latch / 1975 LTD from 12/1974 & 1976/77 LTD w/power windows / 1975/80 Granada/Monarch & 1977/80 Lincoln Versailles w/power windows.

1972/76 Torino & 1972/77 Thunderbird & 1977 LTD II (not an LTD!) with auto seat back latch, and/or with power windows, and/or with power door locks / Ditto 1978 LTD II/Thunderbird before 3/1978.

CARPENTER NOS OBSOLETE PARTS has 27.

GREEN SALES CO. in Cincinnati OH has 34 = 800-543-4959.
-------------------------------------------------------------------
D5TZ-19B888-A (replaced D3TZ-19B888-A) .. A/C Vacuum Selector Valve Assy. (Motorcraft YH-285) / Obsolete

1973/79 F100/350 & 1978/79 Bronco with factory installed integral A/C / 1973/77 F100/350 with dealer installed A/C & Hi/Lo Comfort Vent System.

This valve also includes the "kicker switch" for the A/C compressor.

CARPENTER NOS OBSOLETE PARTS in Concord NC has 293 = 800-476-9653.
---------------------------------------------------------------------------------------
D5TZ-18502-A .. A/C-Heater Temperature Regulator Valve (Motorcraft YG-164) / Obsolete

1975 F100/350 from serial number V80,001 & 1976/77 F100/350 with factory installed integral A/C

CARPENTER NOS OBSOLETE PARTS has 215.
--------------------------------------------------

 

Can you shoot me 1-9 I have the 79 schematics and they are completely different, Ill PM my email. Thanks Brother

 

Number: is that the same relay for horn, seat belt warning etc?

 

Go here for the wiring diagrams. They don't have the '77 yet but the '76 diagrams are basically the same.
You're correct, there were major changes made in the '78 model year.
1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net

 

The D2LY-14512-A relay is not listed for the horn or seat belt warning lamp.

Here's the horn relay (I memorized this number decades ago). I'd have to look up the number for the seat belt warning lamp relay (if there is such a thing), because I haven't a clue what it is.

D6TZ-13853-A (replaced D3TZ-13853-A) .. Horn Relay (Motorcraft HB-112) / Obsolete ~ Available NOS & from auto parts stores.

1973/77 F100/350 / 1975/77 Econoline / 1978/79 F100/350 & Econoline with factory installed Speed Control.

1978/79: No factory Speed Control, no horn relay!

 

Looking at the schematic it functions exactly the same. It is a SPST relay so easy part to get since Im more worried about functionality rather than originality. Thanks everyone