I am NO EXPERT, but since you have already said you replaced the upper wiring harness, I would lean towards the ETA deterioration and shorting out the wiring. On Ebay, search for a Throttle Actuator and you will find an outfit out of Alabama that will rebuild yours for $269 or so. I plan to remove mine from my '95 SL500 and ship it out. I have already replaced upper and soon the lower wiring harnesses on mine and they were "shot". There is no reason to assume that the remaining wiring for the ETA is intact. Let us know what you find out and Good Luck finding the cause, Steve