I suffered a miriad of problems when I converted over to L.E.D.s on my trailer. Turn signals were terribly faint and running lights were strange. However, the problem turned out that I wasn't getting ~quite~ enough voltage to the LEDs. Apparently there is some internal circuitry in the LED units that has to have perfect voltage from a very good working 3 way adapter (for those with separate turn signal/brake lights) and mine was not. After a trip to Walmart, $15 later, I had a universal adapter that I soldered inplace of the previous unit on my truck and my new LEDs work perfectly and are brighter than ever.

If you want to test the units that you have, remove them from the trailer and connect the wires directly to the battery on your car. Simulate the turn signal by manually touching the positive terminal of your battery to the appropriate wire. Bottom line = they SHOULD work like you think they should and are blindingly bright when working properly and blinking.