Cab switch ground works because HIGH works

Resistor block ground works because LOW works

There is no "Power wire" on cab switch or resistor block

The blower motor gets 12v key on, and that 12v passes THRU the motor and out on the orange wire, so you would see 12v on that wire IF that wire was not Grounded, grounding this wire "completes" the circuit and blower motor starts to spin


For Electricity to work it must travel in a "circle", the word Circuit comes from the word Circle
DC circuits require a fixed + and a -
AC circuits do as well but the + and - Alternate rapidly, i.e. alternating current

Electrons flow thru the circle powering a device, resistance in the circle slows down the electron's movement, they act like choke points lowering the flow, resistance can be on the + or - side of the circle, doesn't matter, flow of electrons is restricted so slows the whole circle, less electrons flow so less power available to the device being powered

Car makers try to use the Ground(-) side to restrict flow as much as possible because its safer, like with speed control on blower motor
If a Ground wire shorts to bare metal on vehicle the very worst that can happen is the device will come on and stay on, because the device itself is a Choke point so limits electron flow
If a 12volt wire shorts to bare metal(-) then electron flow is UNLIMITED, no choke point, so either a fuse blows OR melted wire and SMOKE SHOW, lol

So when ever possible control of relays or lights or fans is done with ground wires

 

Then I am confused. If my grounds are good, and the connections are good, why doesn't this thing work?

Please refer to my picture, where I numbered all of the wires under the hood. What connections should I connect to in order to do that 0 Ohm test you talked about?

 

I don't know why it doesn't work :)

KEY OFF
Unplug the resistor block
On the connector with the wires test black wire
Meter set to low OHMs like 200
Touch the 2 probes together, should see 0 ohms, this tests your meter and probes

One probe on black wire and the other on a ground, or battery negative
Should see 0 ohms regardless of switch in cab setting

Put switch in cab on med. low
Test that wire at resistor block connector, same way as above
Should see 0 ohms, that means switch and Cab ground are OK

Test next wire same way

Now test resistor block itself
Put meter probe on "black wires" terminal in block
Put other probe on Orange wires terminal in block
Should see high ohms, means there is a connection but thru the 3 resistors, if OHM Meter display doesn't change then resistor block is broken inside, disconnected

How did the Blower motor test go?

 

Ok, I did the following tests:

Started the truck. Put the blower motor on Low and turned it on. Low was blowing

• I connected wires 1, 2 & 5 together. NO CHANGE in airflow
• I connected wires 1, 3 & 5 together. NO CHANGE in airflow

I turned off the truck and took resistance measurements. The selector was on LOW

• With the grounds (1 & 5) CONNECTED, I took a resistance measurement between wire 2 and the negative battery terminal. 0.0 Ohms
• With the grounds (1 & 5) CONNECTED, I took a resistance measurement between wire 3 and the negative battery terminal. 0.0 Ohms
• I DISCONNECTED the grounds (1 & 5) and took a resistance measurement between wire 2 and the negative battery terminal. Got OL

What now?

 

I got it working.

When I started this project, I found that the resistor plug was not original, it has been replaced sometime in the past. The connections were just twisted by hand and wrapped in electrical tape. But it had the colored wires coming out of it. On the replacement plug I bought, all the wires were black. So I used the plug I was taking out as a template to show me which color each of the black wires coming from my new resistor plug should connect to on the wires coming from the cab

I kept the old resistor plug, and I was going to run some resistor tests on it, and as I was checking a resistor diagram, I noticed the Orange and black terminals were SWAPPED. IN THE PLUG. I confirmed it by watching a video that had a correct plug on camera. So when I followed the color coding of that plug, I was swapping mine as well.

I just went outside, popped the hood, swapped the orange and black connections going from the resistor block to the cab, and I have all 4 fan speeds now. I've never had such a sensation of humiliation and exaltation at the same time

Thank you very very much for all the help