999 Headlight switching by the dash

Hi. I am trying to diagnose a problem with the headlights on my 999. The fuse and relay are fine, the wiring seems ok (with good continuity everywhere) but the light doesn’t switch on. If I earth the correct relay connection it switches / clicks and the headlight lights. It appears to be a problem around the dash, which should earth the appropriate pin other than when the starter is running.

Has anybody else seen this problem? I’m wondering whether a transistor has failed in the dash, but I’m also going to try to sniff the CAN bus to see whether the ECU is instructing the dash correctly. Any suggestions would be welcome. Thanks.

There’s a wiring diagram in the owners manual,if you PM me your e-mail address I can send it over.
Or look here:


Thanks Kevin. It took me a few more days of head-scratching before I realised that one of the wires to the ignition switch connector had corroded and broken. The voltages at the headlamp relay looked OK but presumably the extra resistance was a problem.

Those type of fault can be difficult to find, especially when you can’t get into plugs and sockets.
Must have been trapping water, that’ what usually rot copper wiring.