here is some more info. Apparently the electrolytic capacitors (elko's) start to dry out, short circuit, and cause the resistor to burn up.



I've been wanting to update this thread for a while with my experience repairing my CWS. I want to give a shout out to brian928 with helping me track down the proper parts.

Here's the back story: I had a bad CWS out of a friend's car (an '87 S4) that was completely TU. No lights, no nothing. I had swapped into my car with a good CWS (an '86 S, same part numbers on the boxes) and nothing came on. So I opened up the bad one to see if I could find out what was wrong. I found the burned resistor. Since I couldn't tell what the proper resistor value was because the stripes were burned off, I decided to open up my good CWS. That is the first picture I listed above. The value came out to 3.32 ohms. Then the capacitors had their values listed on top of them. I replaced them with ones of the same capacitance, but higher voltage on brian928's suggestion. I used a 100mf/50V (originally 100/16) for the large one and a 100mf/35V (originally 100/10) for the smaller one. There were 4 capacitors on my board so I replaced them all. I was able to find all the parts at Mouser.com (no affiliation). They cost me about $2.50. The resistors were 10 cents each with a minimum purchase of 10 of them. The shipping cost was more than the parts. I bought extras just in case.
I pulled all the capacitors and the burned resistor, put it all back together, and voila, everything worked perfectly. The second photo is of the new capacitors and resistor installed. So then I decided to do the same to my still functioning CWS to avert future problems and it still works without problems.

On a related note, seems like Porsche must have gotten a great deal on these electrolytic caps because they used them all over the place. I had repaired my odometer a couple years ago with a new gear when that failed, but it stopped working again about 6 months ago. Thinking the new gear had gone bad I pulled the speedo apart again, but the gear was still in good shape and the speedometer needle was moving so I suspected an electrical problem in the circuit board that controls the odometer stepper motor or the stepper motor itself. I tested the motor with a 12v battery and it worked fine. So I decided to replace the two caps on the little circuit board. Again, got the parts from Mouser for a couple bucks. Soldered them in and I am back in business.

So I hope this gives other folks out there some courage to try to fix their own boxes. All it takes is a couple bucks in parts, a soldering iron, and some patience. If you fail there are always professionals out there that you can send your parts to for a professional repair.

Central Warning ecu before repair (it shows the still ok resistor and the two capacitors that cause the burned resistor problem)

Central Warning ecu after repair