Left high beam problem

I have an unsolved high beam problem on my XJ40 Daimler MY 1992 VIN SAJDKALD4AK657378 with normal square European lights.

Both headlight is working fine at low beam but when I change to high beam the left high beam is not working while right high beam is working fine.

All other electrical items seems working normal.

All other electrical items seems working normal.

When I open the left front realay and bulb failure module and mechanicly operates the left high beam relay the left high beam lights up. Conclusion: electrical relay operation is not functioning.
High beam relay

Can I power the relay with a 12V from any other source to check operation? A normal 12V battery charger? or must it be a much weaker voltage.
Has anyone a solution for my problem. The Haynes handbook only seems to shows a general layout "Typical healight system. Has anyone a solution for my problem. I think I also need a circuit diagram för MY 92.

Lightning Logic Circuit unit shows no obvious defects.
Light logic control

Have you checked to see if there is a dry joint in the hi beam circuit on the board feeding the signal to the relay?

Well, I checked all the diods and they are fine. Couldn´t see any dry joints on either side of the pcb,
Is thera any special things to look for or to mesure?

Does the relay get a signal?
You can operate it by hand and it works, so either a relay (coil) failure or something in the PCB that is after the point where both high beam relays get their signal from. I would guess 12V and run through everything with a voltmeter. Maybe even a small test lamp.
I wouldn’t try powering it directly.

Yes, the relay lights the high beam when forced to engage the circuit manually (pushed by by a plastic pen).
Du you mean that I can use 12V from an extern wire to check which leg on the relay that operates it? and than follow that wire to the broken point?

No, I wouldn’t try that. I would worry about frying something. But I would look for voltage at the coil of the relay. Multimeter woulld be the best way.

If you have voltage, I would put in a new relay (likely a standard type) and if not, look for dry solder joints and hope to find one.

I agree to that. I am also afraid of frying some circuit.
Do you know of a source for a circuit diagram specific for MY92?

When measuring the voltage of each pin in the round black connector it is not the same on left and right side. And wire colour marking does not 100 % match the Haynes handbook circuit.

I don’t, I never had an XJ40, but I think this can be figured out.
There is of course

  1. a signal from the stalk to the board, where the relay is actuated
  2. and then the current passes to the lamp via the failure unit.

Is the round plug in 2.? Then it shouldn’t be a concern since we know that 2. is working (from the relay, as you found out).
If it is before the relay, in 1., assume relay and board to be working.
I would think that working backwards there must be a point in the circuit 1. where, after the stalk, the signal splits up. Left and right beam have individual relays, correct? Where is the other one, where is the signal split in two?

The “relays” in the bulb failure modules are NOT replaceable units. They are soldered into the boards inside the bulb failure relay modules. I have repaired these modules by resoldering suspect solder joints. To find these bad solder joints sometimes requires a VERY strong magnification. Another option is to purchase another used relay module off ebay or similar. However you are not really guaranteed to get a 100% working module that way either.

Are you located in the USA? If so perhaps you might want to consider shipping the module you have off to an expert top take a close look at the boards.