[TR] Overdrive solenoid

[terryrs at comcast.net]

I've driven the TR3A's Type A Overdrive for almost 15,000 miles now, but the OD now fails to engage.  Suspecting electrical, I was able to get it to engage intermitently.  Now not at all.
Tonight I disassembled the transmission housing to get at the solenoid, so I could be sure I was getting actuation.  Apparently not.  The solenoid was toast, melted on top with the upper wire no longer solidly connected (hence the intermitency).  
Clearly it overheated.  Since this was a brand new solenoid from one of the Big 3, it  was (ostensibly) set to correct tolerances from the factory.  Indeed, it did work fine for about 15K miles.  
What did I do wrong?  My guess is this thing was drawing the 15 amps all the time, instead of the brief moment to actuate.
Terry Smith, '59 Tr3A
New Hampshire