[117236]

Heater motor Fix.

The problem:
Blown heater motor resister, melted speed switch, melted wires in steering column

The Fix:
Adding relays in the heater circuit. You will also need to replace your blower motor resistor, and selector switch if you have not already done so.

Parts Needed:
4 relays
10 feet red 12 gauge wire
2 feet black 12 guage wire
assorted crimp connectors
1 fuse holder (30A)

Background:
When I got my jeep the heater resistor was blown, so I replaced it. Next, whenever I would Use the A/C a wire near my ignition switch would begin to heat up and smoke. I then discovered that the blower speed switch was melted. I replaced that, but the smoking continued. I then began to research a solution.

Basically, as the blower motor ages it begins to be less efficient and the motor draws more amps. When that happens, the resistor blows, and typically the blower motor switch begins to melt. The factory wiring for this particular circuit is marginal at best, and just simply overloads as the motor ages.

With that in mind, I hit the junkyard to find a new switch pigtail as it seems the connector melts. I looked at 10-12 cherokees in the yard (every one they had) and all the switches were melted. What does that tell you?

That's when I decided to fix the problem. I didn't want to need to Plan on a new fan ($30), switch ($30) in the future.

Reference:
http://www.jpmagazine.com/techarticles/electrical/154_0710_jeep_fire_prevention/index.html
http://www.naxja.org/forum/showthread.php?t=88091&page=2&highlight=blower+motor+relay
http://www.jeepforum.com/forum/showthread.php?t=564106

How the circuit works:
(simplified version)
When the key is turned on, the circuit is energized at the ignition switch. Power then flows from the fuse box to the blower mode switch to the speed selector switch. Once the speed is selected, power then flows to the appropriate wire in the blower motor resistor, and finally to the blower motor. What I chose to do was to put relays inline between the blower motor switch and resistor.
Here is the relevant part of the diagram:

We will basically be adding relays to the following 4 wires located at the blower motor resistor:
Yellow/brown, Tan, Light Blue, and Green.

I used relays already wired with a pigtail from summit racing this makes wiring easier and everything is color coded:
http://store.summitracing.com/partdetail.asp?autofilter=1&part=VIA-80237&N=700+115&autoview=sku

First, locate your blower motor resistor underneath the passenger kickpanel, you will see all the wires we need:

Then, you need to cut each of the 4 wires on that connector, and wire in the relay:

Basically, all 4 relays will share a common ground and power. Then they have a
"signal" wire, and a "load" wire. The signal wire needs to be wired to the wire coming from the switch, and the load wire needs to be wired to the part of the wire going to the blower motor resistor.

The only problem here is the Dark green wire in the harness there are actually 2, which are spliced at the resistor connector. 1 comes from the selector switch, 1 goes to the blower motor. You need to put a relay on the one coming from the switch. To figure out which one this is, I snipped one (lucky guess) turned on the blower motor to high, and used a voltmeter to determine that the one I snipped was getting power, which means it is the wire from the switch. If you snipped that one that is not powered, splice it back together and snip the other one.

All relays have numbered terminals, the terminal numbers, and wire colors from my relays are below:
Pin Purpose Color
38 power blue
86 ground white
85 signal black
87 load red

Note, if your relays have 5 terminals, one will be numbered 87a, simply do not use it.

If you would like a tutorial on what relays are/ do, please read here:
http://www.naxja.org/forum/showthread.php?t=933445&highlight=relay+wiring

Once you have all the relays splice in, you will need to solder together the 4 power wires, and then the 4 ground wires. You now need to find a power / ground.

For the power:
Solder it to the 4 soldered power wires, and then run it under the dash to the drivers side, right above the fuse box you should find a hold in the firewall. Run it through there, across the engine bay, and tie it into the auxiliary power post. Be sure to put a fuse in this circuit (30A):

For the ground.
Once again, solder a ground wire to the 4 soldered ground wires. Then, I pulled the passenger side kickpanel off. Use a self tapping screw to drill a hole in the sheetmetal. Crimp a ring connector on your wire, and tighten it down:

Tape, everything up, then shove all the relays up under the dash. There is plenty of room:

Once your done you won't even see it. Full Power will be restored to your blower motor, and no more burnt wires, switches, resistors. And best of all, no chance of fire.

Total cost was about $35.

special thanks to balloo93 who helped me understand this circuit when I was troubleshooting my original problem.

 

[crosschecker]

Thanks for the write-up. Hopefully, when I get home the pictures will show up as I'd like to check this out.

 

[117236]

and for those that don't believe me, here's photo's from another thread:

melted blower switch:

melted plug:

Literally the 10-12 jeeps that I looked at were this bad or worse. If you have blown a resistor, you have a problem.

I didn't take a picture of the melted wires in my steering column, but I think you get the idea.

 

[havasu1]

Just curious. If this has not happened yet to an XJ, what's the best fix. Just buy a new blower so the amps don't start to spike?

 

[117236]

Just curious. If this has not happened yet to an XJ, what's the best fix. Just buy a new blower so the amps don't start to spike?

Since you have an 99, I don't know. I know the blower motor switch was re-designed but I don't know about the rest of the circuit.

As for the rest of the guys, the best thing to do is go ahead and put in relays. Even after I put in a new blower motor and switch I was still having problems. The circuit is running at capacity, and any little bit of resistance causes a problem.

 

[kiwicowboy]

A lot of Chrysler vehicles of the late 80's thru mid 90's where wired with minimal sized wire. There has been a lot of recalls because of vehicle fires from the small guage wire melting. I've looked at a lot of Cherokees (88 - 95) that had melted connectors on the steering shaft under the dash board. Take a look at your connectors and you might be surprised to find your's have melted too.

"Nothing wrong with being frugal, but you'll get burned being cheap!"

 

[Djmack]

lesson learned.... if you want to relay just 1 wire, such as your high(dark green) wire, it doesnt work... because your low setting(yellow,lightbrown) wire bypasses the switch and goes straight to the resistor.. therefore creating a relay loop, and the only way to turn the relay off is by manually disconnecting the power.

So as far as this write up goes, From experience... Its all or nothing... and by nothing, i meen burnt wires..burning jeep..nothing left..

 

[Djmack]

 

[delkancott]

A couple questions

Where do the 4 power wires and 4 ground wires come from? Are they existing (if so to what part? the switch?) or part of the relay? Pictures? I would really like to attempt this as my BMR blew twice this week and while I can/will replace the motor, I don't want it to be a reoccurring problem. That said, knowing my electrical shortfalls, I will need to be 90-100% certain of what I need to do before I start cutting/splicing/soldering.

Thanks.

Once you have all the relays splice in, you will need to solder together the 4 power wires, and then the 4 ground wires. You now need to find a power / ground.

For the power:
Solder it to the 4 soldered power wires, and then run it under the dash to the drivers side, right above the fuse box you should find a hold in the firewall. Run it through there, across the engine bay, and tie it into the auxiliary power post. Be sure to put a fuse in this circuit (30A):

For the ground.
Once again, solder a ground wire to the 4 soldered ground wires. Then, I pulled the passenger side kickpanel off. Use a self tapping screw to drill a hole in the sheetmetal. Crimp a ring connector on your wire, and tighten it down:

 

[ergolarry]

Its an admirable write up that you've done for a work-around on replacing the actual faulty part (the blower motor). Certainly looks like you've put the effort into making the wiring work with a worn out blower motor. My concern is that you are asking the wiring to carry more amperage to power the blower than originally intended.

Will it work? Most definitely...for a while. What happens generally is that the bearings in the blower motor wear out, the amperage draw spikes through the roof, the resistor and switch can't handle the heat generated and melt. Your fix will address the amperage draw from the standpoint of feeding the resistor from the battery not the switch temporarily, but what happens when the amperage goes up further? Are you prepared for the wiring and relays to melt, ground out and catch on fire under your dash?

In the interest of safety, its a better idea to replace components that can cause your rig to go up in flames rather than to try to save $30 and 10 minutes to switch out the blower.

Again, good job on finding a solution to the problem. As someone who has had to watch his vehicle burn to the ground over something simple, I urge you to consider the safety built into the factory design. The resistor and switch melting is a symptom of the problem, not the problem itself.

 

[burby]

The resistor and switch melting is a symptom of the problem, not the problem itself.

So I'm really trying to get a handle on this situation before I go re-wiring, etc. Are you suggesting to replace the blower motor, then the melted out wiring, relay and switch?

Thanks,
Mike

 

[Kevin108]

My experience has been that when the resistor goes it takes the plug with it. Is there an aftermarket replacement for that plug yet? My dealer wanted over $100 for that section of harness and the local junkyards here only ever have 84-96 XJs. I took the resistor to Radio Shacked and matched up some insulated spade connectors to the individual connectors in the the resistor and that's worked great for over a year now but having the real connector is probably worthwhile.

 

[vabeachtennis]

and for those that don't believe me, here's photo's from another thread:

melted blower switch:

melted plug:

Literally the 10-12 jeeps that I looked at were this bad or worse. If you have blown a resistor, you have a problem.

I didn't take a picture of the melted wires in my steering column, but I think you get the idea.

What did you use to replace the melted plug? Every XJ at the JY i checked out had burnt/corroded plugs that were basically disintegrating.

 

[burby]

...I took the resistor to Radio Shacked and matched up some insulated spade connectors to the individual connectors in the the resistor and that's worked great for over a year now...

This is basically what I have done as well, but do you remember how many wires there are? My switch was melted pretty badly and I could only see 4 wires to connect. Are there 4 or 5? Thanks.

 

[Kevin108]

I remember 4. I have since acquired a proper plug but if it ain't broke, don't fix it so that plug is sitting in my toolbox next to my soldering iron until it's needed.

 

[burby]

Thanks for getting back to me. After studying the wiring diagram a little better, and with your response, I feel pretty good about it, especially since there is no "off" just low, 2, 3, and hi. Now it looks like I need to replace the blower resistor. Thanks for your help!

 

[Kevin108]

Bear in mind that there are some significant differences between our two XJs and I really don't know anything about your body style. On the 97+ the off position is on the blend switch.

 

[burby]

Ah, good point. Well the original poster has a '95, so if his wiring diagram is from a 96 then I should be in good shape. But yeah, I believe your fan speed selector switch is a dial, whereas mine is almost like a rocker switch.

 

[burby]

Blower switch wiring

So does anyone with a '96 or so know how the blower motor switch is physically wired? I can see on the back of the switch there is an "L," an "H," a "B," an "M," and an "AC." From the wiring diagram at the beginning of this post, I believe that the "low" does not get a wire which meant that I had it wired incorrectly. I'm at a loss since my original connector was melted beyond all recognition. If it helps, my Cherokee has a light blue, a light green, a yellow w/ brown stripe and a peach colored wire. The switch, when looking at it from the back, has 3 prongs on the right, and 2 prongs on the left. The top left has the "L," and the bottom left has the "H." Starting at the top right is "B," "M," and "AC." Any help would be greatly appreciated.

 

[JeffDeWitt]

Yes but...

Its an admirable write up that you've done for a work-around on replacing the actual faulty part (the blower motor). Certainly looks like you've put the effort into making the wiring work with a worn out blower motor. My concern is that you are asking the wiring to carry more amperage to power the blower than originally intended.

...

It IS a very good write up, but I think you're missing the major point. The idea here isn't to band-aid a problem that should be fixed, it's to work around a design defect. The real, proper way to fix this is to redesign the switches and wiring to carry the amount of current they have to carry (which is apparently exactly what Chrysler did in later years). We don't have those kinds of resources and so have to get more creative.

If the system had been designed properly to begin with we would have these problems... and the proper way for a system to fail when a part is drawing excessive current is NOT to burn out switches and connectors, but to blow a fuse!