Wiring In Rear Mudguard

My 2003 America has a rear mudguard from a Triumph Adventurer. The rear indicators are bolted through the mudguard (I've not looked at the stop/tail light yet as i'm not feel brave enough). The wiring passes through the indicator stem and water has also passed through and corroded the inside of the lamp. The whole area inside the mudguard is covered with what feels like a cloth tape which covers the nuts holding the indicators and the holds the wiring to the inside of the mudguard. Does anyone know what this tape is called and where it can be obtained? Alternatively has anyone got a better idea how to protect the indicators and wiring from water and prevent the wiring falling off the inside of the mudguard onto the rear wheel? Thanks.