There's an intermittent fault in a taillight socket, or its ground wire, causing the cruise module to think you're pressing the brake. Make sure you're using the correct bulb installed the correct direction (note the offset pegs) and check all the frame/body grounds back there.
Thanks for the advice and the link to diagnostic procedure.
If I may, I would like to ask a couple of follow-up questions. Since the bulbs for the brake light/turn signals are the same bulbs (undisturbed) that have been in the motor home for many years, I do not think that they are the cause of my problem. However, the intermittent ground fault is a distinct possibility. I did not mention in my original post that I recently also started having a problem with my E4OD transmission not locking up or not staying locked up. I know that it normally unlocks when the brake lights are activated, so there could be a common cause for both problems.
My first question: Is this intermittent ground fault likely to be a short from the turn signal circuit to
the brake light circuit or likely to be an open in the turn signal circuit which is back feeding the ground back into
the brake light circuit? For some reason I have in the back of my mind that the circuit which grounds the cruise control circuit to disable the cruise or the transmission unlock circuit is in the left turn signal. I took the left lens off, inspected the socket and cleaned the contacts of both the bulb and socket. I did not go any further in looking for a ground fault because I do not know what I am looking for. Any suggestions here? BTW, we tow a car and we always check that the turn signals and brake lights on the MH and car are operating each morning before we get on the road; they "appear" to be working properly. That does not rule out a relatively high resistance short some place.
My second question: The transmission problem started happening as we left Kansas City and seems to correct itself after 15-40 miles of driving, if I stop, shut the engine down, restart and continue on my way. At that point I did not know that the turn signals were also a problem. Since the transmission temperature was running at about 220°F
(normal about 180°F) at the torque converter output when unlocked and the engine is running 250-300 rpm faster than normal and the pan temperature was at about 140°F rather than it's normal of about 130°F , I stopped at a Ford garage in Springfield, IL on the Thursday before Memorial Day. They could not even do any diagnostics on it until late Friday and the Service Manager said if my transmission temperature did not get higher I would be alright to continue to our next stop just north of Indianapolis. BTW, we live in Rochester, NY so have another 600 miles to go to get home. Finally
my question, will any diagnostic codes which might be stored be in the OBD computer or in a special computer for the transmission? And would a ground fault show up as a code?
Since we live in our motor home for 7-8 months of the year, I would like to have any repair work that might be necessary done in Rochester after we unload the motor home and get back into our home. I can live with the turn signal problem, but do not want to cause either more damage or start causing damage to the transmission. Do you think it is O.K. to drive another 600 miles, especially if the transmission will not go into lockup and runs at the temperatures above. I always drive at 55 mph so I am not pushing it but there must be something in the transmission slipping.
Sorry for the length of the post and thanks for any advice you can offer.