Blower High Speed Relay Mod (Prevent Blower Switch Failure)

Having found my blower switch is starting to show signs of the high speed terminal getting hot I've come up with a mod to prevent this common issue of the blower switch melting the terminal for the high blower speed by running the ground through a relay directly to ground instead of through the switch.

On high the blower draws around 18-20 amps which is alot to run through a small switch.

Example of what early signs of the switch overheating look like:




Do this mod at your own risk, if you mis-wire something or use inferior parts you could damage something or end up with some melted wires.

This mod will not address the issue of the blower resistor and/or blower motor connector melting but those are relatively inexpensive and easy fixes should they be needed whereas the switch and it's pigtail are not easy to get or cheap.

Time required: 1-2 hrs

Tools Needed:

10mm socket & ratchet or 10mm wrench
Wire cutter
Wire stripper
Crimping tool
Very small flat blade screwdriver
Butane lighter or other heat source
Cap light or other light source (optional)
Soldering iron (optional)

Supplies Needed:

Electrical tape
A few zip ties
3x 12-10 Ga (Yellow) Butt connectors (preferably heat seal type) or solder and heat shrink if you prefer to solder
1x 12-10 Ga (Yellow) 1/4 in ring terminal
A couple pieces of heat shrink (one aprox 5/16 in dia and one aprox 3/16 in dia)
1x 5 pin relay connector with 12 Ga wires (Standard Motor Products HP3810 or equivalent)
1x 5 pin 30A Bosch style relay (Standard Motor Products RY116T or equivalent)


Start by removing the glovebox and floor duct to the left of the glovebox for visibility, the vent can be a bit tricky to remove but a little wiggling gets it free.



Unplug the blower & resistor (circled in red), remove the wire from the white clip (circled in green) by unlatching it, and remove the black wire retainer (circled in orange) by pressing the tabs in with a screwdriver or other suitable tool.




Untape the section of blower and resistor harness circled in red (you may want to wear some gloves to do this as the tape Toyota uses is very sticky and gooey).




Cut the White/Blue wire that goes to the blower resistor near the spot shown.




Slide the small piece of heat shrink over the wire on dash harness side and use your heat source to shrink it then pinch the end shut while it's still warm to seal it.




Here's the relay connector for reference, the pins are also labeled on most Bosch style relays.
The wire colors I'll be using match the connector I have but wire colors may vary so be sure your using the right pin on your relay.





Crimp the ring terminal onto Pin 87 (Yellow) of the relay connector and attach it to the stud behind the upper right corner of the glovebox as shown.




Using a butt connector connect Pin 87a (Orange) of the relay to the White/Blue wire coming from the blower resistor and seal it (always make sure to give butt connectors a good tug after you crimp them but before you seal them to make sure the crimp is good and the wire doesn't pull out).




Cut the White/Blue wire about 2 inches from the blower connector.

Connect the end coming from the dash side of the harness to Pin 85 (Blue) of the relay connector.




Connect the White/Blue wire at the blower connector to Pin 30 (Red) of the relay connector.

Using a small screwdriver carefully pry out the latch on the blower connector.




Using a mini screwdriver or other suitable tool carefully push back the tab (circled in red) to release the Black/Yellow wire terminal from the connector.




Carefully strip a small section of insulation off of the Black/Yellow wire (take care to not cut any strands of the wire) a couple inches away from the blower connector and connect Pin 86 (Green) of the relay connector to the Black/Yellow wire as shown. I soldered mine but it would probably be fine without it as the relay draws very low current.




Slide the larger piece of heatshrink over the wires and seal it. Re-install the pin into the connector and insert the latch, it should look like this when you are done.




Plug your blower motor and resistor back in and test everything, if it's good then re-tape all the wiring and put it back in the proper places.




Tuck the relay up next to the harness by the PCM and secure it with a zip tie.




Re-install the floor duct & glovebox and your done, now when the blower switch is on high ground will be supplied through the relay instead of the switch.


Here's a wiring diagram of the mod.

 

Nice work.

Thanks for the excellent DIY

 

Ditto. !!!

 

The burnt connectors are from a weak connection it's not caused by the blower. With the industry trying to save money cheap and easy to install and plug in it's not just a Tacoma issue. In the winter more than anything my heater is on full speed ahead kind ah gets that way up north. The various speeds are controlled by the resistors for each speed, the resistor resistance is what lowers the speed, the greater the resistance the slower the speed.