Warning light mystery.
 

I'm working on a 86 XJS VDP. When I step on the brake, or turn the headlights on I get a bright yellow indicator on the speedometer gauge which I can only assume means that there is a bulb out somewhere.
I put all new bulbs in the tail lights and they all work properly. I also verified the running lights and headlights are all working. All the interior lights except for one map light are working. Also, this light will eventually go out after about ten minutes with the headlights on. Anyone know what I might be missing here?

To clarify a bit, it's normal for the bulb failure unit to come on whenever the lights are switched on. However, if the bulbs and circuits are good it should extinguish within 15 seconds or so....not ten minutes.

The bulb check circuit will also "test" the brakes lamps by applying the handbrake and stepping on the brake pedal. If the warning lamps glows the brake light bulbs are OK. Weird, I know, but that's how it works.

So, in your case, the parking brake is applied when you touch the brake pedal or the circuit "thinks" that the parking brake is applied. If the parking brake isn't applied it could be a faulty parking brake warning switch which stays closed even if the parking brake isn't on.

The warning light staying on so long could be a faulty bulb failure unit (there are several) or incorrect bulbs have been installed. The system depends on heat from the various lamp circuits to operate properly. If a bulb fails, or if a bulb does not have enough current draw, less heat is created in the circuit and the warning light glows.

Cheers
DD

@ Doug Your knowledge of the electrical system is amazing! Thanks for explaining how this alarm light is meant to function. I poked around on some of the connectors and wires on the bulb failure units. Not sure what fixed it, but its working okay now. The light goes out after about five seconds. :icon_razz::icon_razz::icon_razz::icon_razz::icon_ razz:

Probably loose/dirty/corroded connections....the root cuase of most of the ballyhooed and infamous "Lucas, Prince of Darkness" horror stories.

Spend a Saturday cleaning every fuse, connection, and ground that you can put your hands on. It'll go a long way towards happy Jaguar-ing :-)

Cheers
DD