XJ6 electrical gremlins,check the bullet connectors first

Jaguar used Lucas bullet connectors throughout the XJ6 wiring loom and they corrode over time, causing intermittent electrical faults that drive you mad. Before you start chasing wiring diagrams, pull apart every bullet connector you can find and clean the contacts with fine emery paper and apply dielectric grease. Focus on the engine bay loom where heat and moisture do the most damage. I've fixed more XJ6 electrical problems with a pack of emery cloth than with any diagnostic tool.