Boxster 986 - No high beams, really strange symptoms.

[Shandy]

Ok, this is a strange one. Last night both of my high beams stopped working at the same time. No high beam light on the dashboard using the high beam selector, pushing either forward or backward on the stalk. I thought it would either be a fuse or a bulb and that if either side stopped working the other side must be disabled too. So this morning I checked the fuses, both are fine. So I pulled the headlight units and tested the bulbs. All OK (tested with multi meter and with a 12v source, they lit up). This is where it gets really strange:

- With both headlamp units removed from the car the high beam indicator light on the dashboard lights up when I use the high beam selector stalk.
- I tested the female connector socket for the headlamp unit and confirmed there is 12v both sides with the headlamp units removed from the car when the high beam control is activated.
- As soon as I refit either headlamp unit to the car there is no longer 12v to the other side connector socket when high beams are activated. The fitted headlamp high beam does not work either.

I really don't get this! Anybody have any idea what to check next? Fuses all OK, bulbs OK and the switches seem to be OK.

Thanks in advance, Paul