Don't forget the relays. Swap the up relay with the down relay and see if it suddenly goes up but won't come back down. If so, the relay is bad. There's a relay chart on my website under "Where Is It?"
Good luck!
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1987 928S4 Silver Metallic (980)/Navy (TP) 5-Speed
2000 Boxster Speed Yellow/Black 5-Speed
1966 Wife White/Brown Top
1986 Daughter White/Brown Top (Sold!)
1992 Daughter White/Blonde Top