towing light not working
 

I just installed the OEM tow harness on the 2002 ML 500. The turning light and the brake lights are not working, however, when I turn on the parking lamp and headlamp, all the lights on the trailer lites up but the turning and brake lamp still don't work when I press on the brakes. Could it be the harness or the 7pin to 4pin converter. I lost the original 7 to 4 pin converter so I bought an after market one, could that cause the problem?