Power tilt problem

I have a 140 evinrude outboard

I have a 140 evinrude outboard 93 vintage that the power trim will engage automatically after the engine has been running awhile. It sounds like the motor engages and dropps the engine to its full down position. It also sounds like the motor trys to continiously run in this position. When i raise it up it may stay up for awhile but then its starts downward on its own. im afraid the tilt motor will overheat or damage the wiring. usually the engine runs about an hour before this occures. i have twin 140's the other tilt works ok. any ideas's

"That condition is usually due

"That condition is usually due to having an intermitent short in one of the PTT switches.

Disconnect the PTT power wire at the PTT switch which is on eht engine. If the problem ceases to exist, replace that switch.

If no change, do the same procedure with the other PTT switches.

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc"