Need some help/advice had a suzuki swift 1.3 since Jan, had a new clutch fitted last week due to slipping just before that I had been having a problem when coming to a stop once i pressed the cluth the revs dropped to 200 and the car shook, was hoping the new clutch would fix the problem but its still there, the garage that did the cluth said there were no vacumm leaks, and could not fin any other problems

I am stuck what to do next, when looking under the bonnet tonight on the left side of the engine below the brake servo I noticed in the wiring there was a connector that was not connected to anything it has 3 wires a peach one a red one and grey/red one I can not see anywhere this could of come from does anyone have any ideas on what to try next?