Hi everyone,
I recently purchased a 1990 XJ40 Vanden Plas Majestic. I love it and it drives great. However, in the past day, it's developed a quirk. When I start the car, it seems like the security system triggers. The car will honk and the headlights will turn on. It has happened three times. Two times, I turned off the car after a couple of honks, waited 10 seconds, started the car again and it was normal. Once, I turned it on and it only honked and lit up the lights once. It was normal after that and I proceeded to drive. Does anyone know what may be the cause and how to fix it? Thanks for your help.

 

Hi dursted13,

Welcome to the Jaguar Forums! It's great to have you with us.

My first question is whether the security system is factory or aftermarket?

I don't have enough knowledge of the security system operation to have a definitive theory. My one thought is that I believe the Central Microprocessor (CPU) is involved in the horns and lighting and that water ingress of the CPU due to clogged drains below the A/C evaporator in the dash is known to lead to various problems. When the drains become clogged with deteriorated insulation foam, water pools under the evaporator and sloshes out onto the CPU.

Another possible cause is a door or trunk lid that is not securely closed. Is there any indication of this on the instrument cluster?

You can download the Electrical Guide at this link:

Jaguar XJ40 Electrical Guide 1990

Hopefully other members will respond with more specific ideas.

Cheers,

Don

 

Hi Don,
Happy New Year, and thanks for responding.

As far as I know, it's the factory security system. As far as your A/C theory goes, my A/C doesn't blow cold, so I haven't used it since I bought the car a few weeks ago. Could pooling still occur despite that?

The trunk and the doors were fine when I checked, and the instrument cluster doesn't indicate otherwise.

I've started the car nine times since posting, and this problem occurred once more.

Thanks for the help!

 

Sorry, I meant the problem occured one time.