Improving blower motor performance

On 1984 to 1990 MJs and XJs, the blower motor’s factory grounding point is on the driver side inner fender under the sheet metal screw. This ground is shared with windshield wipers, front windshield washers, rear windshield washers, AC clutch relay, fan control relay, fog lamps, fan motor, headlamps, front turn signals, front side markers, and park lamps.

So your blower motor has its ground point 10 feet away from where it is located!!

What we’re going to do is leave that ground intact and also ground the blower motor on the passenger side inner fender much closer to the blower motor itself. This will also benefit the other components on the factory ground circuit. Take this opportunity to refresh the factory ground as a matter of course. Remove the screw, scrape the surface to bare metal and reinstall the screw securely.

Here’s what I do to get the ground much closer to the blower motor and add another ground point to this overloaded ground circuit.

Find the blower motor connector on the passenger side. Red and Black two wire connector.

Find a location where the black wire can be made to reach the passenger side inner fender, and cut the wire. You may have to do some rerouting of the harness to achieve this.

Take both cut pieces of wire and put them together into a yellow eyelet and crimp. Fasten the eyelet to a place on the passenger side inner fender with a sheet metal screw after applying OxGard to the contact surfaces. Be sure to scrape the attaching point on the fender to bare metal first.

Your blower motor will now turn faster and last longer, and the other electrical components on the circuit will benefit from a better ground path.Blower motor factory ground Blower motor new ground

Revised 01-31-2016

30 thoughts on “Improving blower motor performance”

  1. It should probably be noted that one of the easiest ways to improve a device ground is to simply use a “local ground” – read: “a mounting screw.”

    I do this as a common practise, as long as I can get at least one screw positively into the sheetmetal. Clean the contact patch (it need not be large!) down to BARE METAL, apply corrosion inhitibor liberally (something akin to Gardner-Bender’s Ox-Gard – there are specific products for this. Don’t substitute…) and reassemble.

    This is an effective solution for pretty much anything that grounds directly to the chassis, or any added accessories (when I add lights, I usually ground them through the mounting bolts.)

    The other advantage to this is that you really only need to run one wire to whatever – for power. Simplifies things…

  2. Hey – great to see another tip added to the list! FINALLY got your PM on CherokeeForum & added your website & the .pdf version to my site. MANY thanks for helping keep the old RENIX Jeeps alive!

  3. A note on crimp connectors.
    I crimp them well.
    Then I solder the visible end of wires.
    Don’t over solder and crowd the connector end. Just enough to insure the wires are well connected and won’t pull out of the crimp.

  4. Any ideas as to why a blower motor only works on high? I have replace the switch in the heater controls, the resistor twice and the blower motor itself.

    I have not done the ground wire mod but will when I finish my Kelley’s WIP install. Thanks for all the great tips and info.

  5. Hi Cruiser and thanks for your time and effort here.

    I have an ’87 Wagoneer and yesterday was the first time we had it out in single digit temps. The blower motor started only after the engine warmed up for awhile, a few miles and some idle time then it kicked in. I will do this mod but don’t want to get caught far from home and have it poop out on me. Is this a likely fix or should be looking for something additional?


      1. Made myself go check it today, mostly because we need it Thursday. 🙂 We were minus 44 here Friday night.

        I don’t doubt this is the realm of possibility, especially since there are no other wires close to like this but they are black and green instead of red. Have you seen this?

        The PO has worked them because both wires are taped. I will have my tiny hands helper open them up tomorrow and see what they look like.


          1. Yes, the POS is interesting. The neutral start switch clean job was worked around by running a wire from the battery across the top of the engine to a momentary switch under the dash then back to the starter relay under the relay cover for when the NSS didn’t make contact.

  6. Hi Cruiser, On ’87 XJ Wagoneer, 4.0, I get hot (have not checked with A/C) air from the defroster and from the rear seat outlet at the back of the console but essentially none out of the dash vents. Thinking it must be vacuum but not sure where to start looking.

    Also, can you point me on doing a new post on the Cherokee forum?


    1. It’s most certainly a vacuum issue. The storage container for the vacuum is inside the front bumper on the passenger. side. The hoses deteriorate over time or the container can be missing or cracked.

      Vacuum diagram

  7. Hi Cruiser… happy new year. I have some detailed questions regarding the a/c evaporator, and I don’t see a better place to post the question? I’m working on my son’s’ 90 XJ. We had to replace the heater core. What a PITA!

  8. I have done this mod, with excellent results. Quite noticeable, actually. I took it a step further, and ran a relay between the battery, and the fan motor that is activated by a separate switch. Yet another huge improvement. And with a black XJ with no carpet, or insulation, you need all of the A/C fan you can get!

  9. Hi Cruiser, I have couple of questions – one easy and the other a poser. The easy on is very short so i am including it here even though it belongs with sensors.
    I have a ’87 Renix Cherokee with over 300k on it. What is the sensor about midway along just above the oil pan flange on the driver’s side (below the manifolds)? Mine is crumbling but I can push the two conductors back into it and it seems to stay – don’t notice any difference though. Knock sensor?
    Now the puzzle: Couple of years ago I replaced the blower fan motor due to squealing and slow movement. Ran great for a bit then just had top speed. Replaced the resistor pack due to multiple suggestions that this is why just high speed. Wasn’t sure about the switch and so I replaced that also. (great to have cheap parts) Now it blows the 25amp fuse after just a few seconds any speed. Pulled the fan connector and checked ground and have approx .01ohm, then used an old 10 amp battery charger (no computer) and the 15 amp scale reads about 14amps with the fan at what sounds like full speed. I even tried a 30amp fuse (I know, not a good idea but I am running out of good ones) and same thing, popped after 3 or 4 seconds. Any suggestions? what am I missing here? Oh, and is there any reason not to go direct to the ground post on the battery for the ground upgrade, since it right there?

    1. That is the knock sensor.
      Going to the negative side of the battery is a great way to improve grounds.
      What happens if you disconnect the blower motor and turn the blower circuit on?

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