1998 White Onyx Jaguar VDP (X308) 4.0 without supercharger.

I decided I could no longer endure the exploding (leaking) interior rear view mirror. I've spent well over $300 repairing damages thus far and still need to get the black J-Plate, hopefully without purchasing an entire shifter assembly. So anyway, I replaced the factory mirror with a Gentex mirror that provides several other functions but NOT the Jaguar specific Auto Headlamp control function.

Assuming the factory auto headlamp control that WAS in the rear view mirror set a signal (presumably some voltage level) indicating the need for headlights to be on (while lamp control is in the Auto position), I feel that I could fix or set a "it's dark outside" signal permanently at the plug in the upper console and have the equivalent of DRL (Daytime Running Lamps).

What I am hoping to find is someone with knowledge of that signal and how it is presented at the wiring harness in the upper console. Thanks, Tom Howell

EDIT: Found the full electrical schematics for XJ Series 1998 and it appears as though the signal from the lighting stalk while in Auto position is placed on the YU (Yellow/Blue) to the mirror plug in position 5. This narrows my query to needing to understand what the actual function the light sensor in the mirror served and at what voltage level (presumably at battery voltage level). I am thinking that clamping this wire to the mirror ground may be the answer but a dead short would be very destructive if I am wrong. Again, your knowledge and experience is greatly appreciated.

 

Look at page 123 of 158 in the wiring diagram. It says that is a momentary ground for "headlamp dip request".

 

Thanks avt007. I noticed the GROUND (MONENTARY) so I traced the circuit back to the lighting stalk and noticed that DIP and SIDE are bound while in the AUTO position (Fig 11.5, page 65 Electrical Guide) and (wrongly) assumed that the momentary request was in support of a headlamp flash request as performed on the lighting stalk.

DIP and SIDE are bound to signal ground while in those switch positions leaving me to believe the mirror connection effectively did the same thing while in AUTO. The presence of the Active statement GROUND (MOMENTARY) is what has kept me from clamping that service line (YU) to ground. Silicon logic is my forte with current limits at a 5V level; not quite comfortable yet with the automotive 13V B+ logic.

My next step is to build an inline fuse (for trial purposes only) for small current limit and clamp that YU to the ground; go through the various positions and activities (flash, highbeams, turns signals, 4-ways, etc.) to see the impact (see if it works or pops the fuse).

Thanks for looking. Tom Howell