Blower Motor Variable Speed Malfunction (not the resistor)

It's been a really long time since I have had to log into here. Some how I am still limping along in my 05 tacoma I rebuilt back in 2010. The latest issue now is the A/C blower motor will only work on high.

1. I know, the first response is did you replace the resistor...? yes I tried three different ones, either Amazon, napa, and auto zone, all sold me a defected resistor or it is something else.
2. Then I replaced the connector at the resistor, it was a little toasty looking but overall it looked useable, but I replaced it anyway. Soldered and heat taped.
3. Then I got serious, I tested the selector switch, wire connectivity between the resistor and the selector switch, connectivity between the selector switch and the relay, replaced relays, checked all fuses under the hood. then finally I replaced the blower motor.
4. not really sure what else to do or replace.

My understanding is this circuit is not that complicated so this one is driving me a little crazy. I uploaded a screenshot of the wiring diagram, if I missed something please let me know.

 

It sounds like you have done a pretty good check of all things.
I didn't see where you tested the resistor ground.

I take a test light and see if it lights up when I probe the black and white wire on the resistor connector.

 

See my post here from a few weeks ago. Look for the 4-pin harness in left side of passenger footwell

https://www.tacomaworld.com/threads/2007-trd-sport-hvac-fan-light-issues.841464/#post-30109669

 

thanks, I have not checked this yet!

Can you be more specific, are you talking about the 4 pin harness that plugs in the resistor? I read your post and it sounds very similar to my issue, at one point I even had weak power going to the other speeds, but now it is completely off. I’ll get under there and start moving things around when I go check the ground to the resistor. Maybe I’ll get lucky.

 

Well I caught some luck. I started moving the resistor harness around and things started intermittently working. I even had everything working as it should but then after I put it all back together, the same issue came up. I think I narrowed it down to a bad connection between the aftermarket connector I replaced and the resistor. I started bending pins on the resistor to make better contact with the connector and that worked until I put it all back together. Then it didn’t seem to matter how well the connection was so I took the resistor and tested it with my ohm meter and it was way out of spec. So maybe by messing with the pins I screwed it up too? Anyways I ordered a matching Dorman set with the resistor and connector, I’ll see if that works better for me.

 

AC fan circuit carries some decent current which can cause heat buildup at the connector. Over time it takes the temper out of the female parts of the connector which causes disconnects as it heats up, that's the reason wiggling the connector will make it start working for awhile. A loose connector creates additional heat which compounds the problem.

Have you ever stayed in a hotel and plugged something into a receptacle and have the plug fall back out or be loose? Same issue, no temper left in the metal parts of the outlet from frequent heat cycling. I doubt you damaged the resistor but it's quality might be an issue.