This is how I replaced the HVAC blower motor resistor in a 2005 Tacoma.
Symptom of a bad resistor for me has been that the AC/heater blower will only work on high. At first this is intermittent, then later pretty much constant.
First let me say that this is the 3rd resistor for this truck. They seem to last me about 18 moths. The first replacement was under warranty, and after they checked everything else out they decided to replace the resistor. Once they decided it took the guy 15 minutes or so to replace it. A few days ago I called the local stealership, the service estimate was 1 to 2.5 hours labor and $38.17 for the resistor (MSRP $28.89). That's why I decided to do it myself.
The first problem is finding where the darn thing is. By looking at the service manual it appears to be next to the blower motor, actually it sits right next to the firewall a little to the left (drivers side) of the blower motor. Now a skinny little guy could get to it rather easily, but for a big old fat guy like me (59, 6’6”, 325lbs) that isn’t at all limber - not so easy. I tried to get up under there but just couldn’t my head and shoulder jammed in enough get a good view.
I ended up pulling the front passenger seat for access. It still isn’t easy - but at least do-able.
Now that I know where it is I believe that I could change it without removing the seat.
First step after you find it is to disconnect the wiring harness, it comes off pretty easily, next there are 2 screws holding the resistor in. There is one on the left as you look at it, there is a second one on the right in about the same position - but on the back of the unit and pretty much not visible. I couldn’t see it no matter how far I got under the dashboard.
You can feel it though. You will need a 5.5mm socket on a ¼” drive ratchet. It needs to be a ¼” drive because anything bigger won’t fit on the back screw and in the space available. As it is I had to pull the carpet out of the way to get on the hidden screw.
Remove both screws and the resistor falls out in your hand, put the new one in, making sure that the little catch on the resistor for the plug is facing you.
Start both screws, and lightly tighten, connect the wiring harness AND . . .
That’s it you are done.