Per what I was told when mine went at about 39k, the reason the "card" resistor was abandoned for a thicker design was because of premature failure. The one I put in is still working great at 160k.

 

First off, thanks for this quick, down and dirty, help guide. Now for the bad news. I pulled my old resistor out and its in perfect shape BUT the wiring harness connector had one wire that looked a bit corroded and loose. Actually, loose is an understatement. It came out the minute I touched it. It looks like it has overheated the connector on both sides (resistor and harness). Has anyone else had this? How hard are the wiring harness connectors to buy, install?

 

Ouch! It's hard to say what the availability of the connector will be, I was able to buy a headligh switch connector and pigtail for a Cherokee at the dealer, but it's fairly common for them to develop bad grounds and overheat the switch. Definitely check before hitting the salvage yards

Also, if it looks like it was melted, check the grounds for the switch and fan, and replace the resistor anyway. If something did overheat it, it'll happen again if the primary issue isn't corrected.

 

I got my resistor at Parts Source in Canada (A Canadian Tire Company), for $27.00. It was like changing a fuse, but you have to get the panel off that is UNDER the glove compartment on passenger side. They even sell them for $12 on internet but shipping cost dont make it worth while.

I did NOT have to file the new unit, it just popped in and looked exactly like old one. The only concern is, the unit smelled a bit like burning for a few days. Nothing was touching, so not an issue. When you take the old one out, it can be repaired, the 'resistor' at the TOP of the unit just pulled out, is called a varisistor(a transistor solderer across the top). It acts a a current surge protector, to avoid the other resistors from burning out. This can be replaced like a diode, and costs pennies to buy on ebay, however I have not been able to get one for around the 13-16volts. The varisistor has to go in one direction only, like a diode. If you want to jimmy the unit, just solder a paper clip across the top and fan will work on ALL speeds. I do not advise this, as if and when you do get a power surge, you have no protection! Just good to know for testing purpose.

So why does the resistor burn out? Well there are several reasons. Only read on if you have REPEATED burn out issues, otherwise dont bother worrying about it.
1) The Alternator is putting out too much voltage and creating a surge on engine startup etc, causing resistor to burn out. To do a simple test I put a volt meter inside the cigaret lighter, plug in type with LED read out ($5.00 on ebay) and start engine and read out should not surge past 14.5 approx or fluctuate that much. If it does flactuate a lot, then over haul alternator. See Youtube video on alternator.
2) The heater fan brushes are worn or fan motor needs replacing. I don't think on these new motors one can change the brushes.