2005 Dodge Sprinter Blower motor blowing weak

Its a five cylinder by the way not four. The heater air conditioning blower motor blows weaker than normal on all four speeds. If I remove the insulation under the hood exposing the blower motor and plug into the blower. If I wiggle the plug it operates at full normal speeds for a while then returns to weaker blowing power on all four speeds. Is it the plug and or blower motor or other.