Need wiring description for the back of blower switch

Tiny
MTOMEK
  • MEMBER
  • 1992 FORD E-SERIES VAN
  • 7.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 235,000 MILES
Went to replace the blower switch on my E350. Some time prior to me purchasing the vehicle, they cut the plug that attaches to the switch.
My problems is that I don't know which colored wire goes on which terminal on the back of the switch.
It is a four way switch, and there are four wires that need to plug onto the 4 terminals on the back of the switch.
Any help please?
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Monday, January 13th, 2014 AT 5:57 PM

6 Replies

Tiny
CARADIODOC
  • EXPERT
Sounds like you have a three-speed switch and an old one burned up and melted the connector body. You aren't going to hurt anything by mixing up where the wires go because there is no ground wire there. You can find the 12 volt feed wire with a test light or voltmeter. It will only have 12 volts when the ignition switch is on. If you can identify the common terminal on the switch, that's where the 12 volt feed wire goes. From there, trial and error will tell you if you have the other three wires in the right places.

If you can't tell which switch terminal is the common one, you can use an ohm meter to find out. Regardless which switch setting you pick, there will always be continuity between two terminals. That will change depending on the setting, but you will find that one of those terminals is always one of the pair. That's the common one that gets the wire with 12 volts.
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Monday, January 13th, 2014 AT 6:24 PM
Tiny
MTOMEK
  • MEMBER
I took a look at the wiring. There are four wires for the back of the switch which includes a black wire that I'm assuming for the ground.
I have no power to the switch. I'm guessing one of the wires needs to be hot, but none are.
Checked all fuses inside, and under the hood, and all are good. I don't have any power to the switch.
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Tuesday, January 14th, 2014 AT 4:24 PM
Tiny
CARADIODOC
  • EXPERT
You are right, and I messed up. As usual, Ford is doing everything backward compared to everyone else. The closest service manual I have is for a '96 van, but it does indeed show a ground wire at the switch. Everyone else feeds the switch with 12 volts, then the different switch positions send current through a different resistor, then to the motor and to ground. On yours, the 12 volt goes right to the fan motor, and from there to all the resistors, then one of them is grounded by the switch. The common terminal on the switch goes to ground, and that is shown as a black wire.

In my diagram, current starts at a 60 amp fuse which will be under the hood and it will feed other systems. Next, it goes to a blower motor relay, then to the motor. It looks like all of those components are under the hood. From there, there's a lot to describe related to tests and observations, and rather than cover everything, start by listening to the fan motor. With the switch totally out of the circuit, the fan should still be running on the lowest speed with the ignition switch on and the heater mode switch on any setting other than "off". If it does, everything up to that point is working and you should find some voltage on the orange / black wire at the switch. If there's 0 volts on that wire, suspect a corroded connection at the firewall connector. You can verify that by checking for some voltage on that wire at the resistor assembly. The voltage should be the same at both places. For this type of suspected problem, a test light is much more accurate than a digital voltmeter.

You can also check the voltage on both motor wires. The orange / red must have 12 volts. If it doesn't, we have to go to the relay to see if it's turning on.
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Tuesday, January 14th, 2014 AT 9:11 PM
Tiny
MTOMEK
  • MEMBER
Appreciate you help. Started to get frustrated.
I work better with a light than an digital voltmeter.
I will try this, and see where it gets me!
Thanks Again!
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Wednesday, January 15th, 2014 AT 10:21 AM
Tiny
MTOMEK
  • MEMBER
Could not figure out why? I followed all you steps, and I still was not getting any power. Finally swapped it out for one at a salvage yard, and I got it to work.
Thanks for your help, and looking over the old, and the new, I discovered that the lever that switches from A/C to vent, heater, defrost, and so on, was broken off inside the vacuum switch.
A little piece of broken plastic was the culprit! Kept the fan from turning on.
Thanks for the help.
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Wednesday, January 15th, 2014 AT 2:27 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. I helped solve one in a row!
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Wednesday, January 15th, 2014 AT 5:06 PM

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