Arthur, Thank you for the offer of schematics. I do have the MB Electrical Troubleshooting Manual. I agree with your diagnosis of a bad relay or an open wire. I forgot to mention that I jumped the temperature switch and the fan did not come on. Since both the K9 and K10 relays have the same part number, what role does the R15 auxiliary fan preresistor play? I do not remember seeing one when I traced and tested the wiring. Brutally hot and humid out and I do not think I will get back to troubleshooting this afternoon. I live across the border in MA. You know what I mean. Thanks for all the responses.