SD speedometer woes
 

83 300SD. The speedmoter sometimes works, somestimes does not work and it is making me a little nutty. I have cleaned the contacts where the wire originates at the back of the trans and made sure that there is a firm connection. Likewise where the speedo plugs in at the back of the instrument panel. The speedometer might work correctly for several days and hundreds of miles. Then all of a sudden it works intermittently. Here is a possible clue. When the speedo in not working and I am driving along and then brake to slow down or stop, the speedo needle will work for a couple of seconds and then drop back to zero again. ??? Any ideas out there? By the way, this forum has been a great resource. Thank you.