2008 wiring diagram below

The Blower motor gets 12volts when selector is in ANY position except OFF, this closes Blower Motor relay in engine fuse box

The Fan Speed switch is the GROUND for the blower motor

You have to keep that in mind when testing with voltmeter

So Resistor block routes Ground thru the 3 resistors, all 3 resistors is low, then 2 resistors is med 1, then 1 resistor is med 2, then no resistors is High
High by passes Resistor block

So if High doesn't work then check Blower Relay or Blower fuse in engine fuse box, it is possible the GROUND in the cab for the fan switch has come loose but a real long shot, and this wouldn't effect low or mediums, because they use a different ground, as seen on diagram

If high does work, but not low, and mediums, then resistor block wiring is most likely issue, check its Ground, pin #3 in diagram, if this wasn't good then no lower speeds would work

 

This post made me finally go fix mine a few minutes ago. Been meaning to for months now. I wrapped sandpaper around a mini-screwdriver and kept sanding the rust off of both sides of the male terminals inside of the resistor unit. I'd already replaced my wiring harness connector a couple months ago with a better looking unit from a parts truck as well as the resistor pack. Filled it up with dielectric grease and no-go. Wiggled the connector into another position and it worked on all speeds. Looks like I've got a little more sanding/cleaning to do on my connectors/terminals... but I ran out of daylight.



GB :)

 

Heads up on dielectric grease, it does NOT conduct electricity, which is the point of using it on electrical connectors, but not INSIDE the connectors, if you get it on the metal contacts then..................it does what its suppose to do, prevents water from coming in and PREVENTS electricity from flowing

 

 

 

Good work, thanks for the update

Hope you don't hit a DIP(opposite of bump), and is stops working again , lol.

 

I use it heavily in everything, from all sorts of bulbs, connectors, and even plug wires. In and on the terminals. Never the slightest problem.

The male terminals on my resistor pack were dark brown with very heavy rust so that's where my continuity/conductivity issues lie.



GB :)