Please tell me where to find the hidden inline fuse for the horn. I have found the one in the fuse block and the relay, both of which are fine but I am advised that there is a hidden inline fuse for the brown wire that feeds the horn relay.
please tell me where to find it on a1985 left hand drive XJS V12. I’ve checked by the brake servo and by the battery but it’s not there. Please send detailed instructions and a photo.
thank you.
Charles

 

There is no hidden fuse; BUT there IS an extra fuse in the system that is not on any Jaguar diagrams.
On the inner wing LHS there is a fuse block with four or five fuses. The frontmost fuse is on the diagram as fusing the auxiliary cooling fan. It ALSO fuses the horns. Check this fuse and the fuse holder.

 

I know this circuit well as I spent part of yesterday getting my horn to work again. If you pull the horn relay are you saying you have power at terminals 86 and 30?

 

Good mornign Greg,
Thank you for your reply.
I WAS aware that the horn shared its second fuse with the auxiliary fan, and I had already checked that fuse twice and it appeared to be fine. So I was looking for another inline fuse.
However, after rethinking this logic, I decided to check all of the fuses with a continiuity tester, and I found that the auxiliary fan fuse had no continuity even though the link inside appeared intact. Aparently, the metal bar must have detached from the metal end cap which was not visible through the glass tube.
I replaced that fuse with a fresh one and my horn now works.
Ironically, all of the other fuses are 7 year old British fuses and they are fine but this one was a much newer American replacement and it had no continuity, so that was the culprit.
Now on to the next problem!
My "bulb out" indicator still comes on whenever the lights are activated even though all of the lights are now working properly.
Any suggestions or ideas for that fault?
Thank you,
Charles

 

Good sleuthing on the faulty fuse...which pop up from time to time


It's normal for the bulb failure warning to come on for 15-30 seconds whenever the lights are switched on. Then it turns itself off.

If the warning stays on, post back

Cheers
DD

 

Yes, the “Bulb out” indicator stays illuminated as long as the car is running with the headlights or parking lights switched on.
Curiously, I had diagnosed a faulty trunk (boot) light switch that allowed the boot lights to stay illuminated with the boot lid closed.
Initially, I had removed the boot light bulbs to preserve my battery and then the “bulb out” indicator performed as intended. It would illuminate initially when headlights or parking lights were activated, but it would go out after 15 seconds.
After I repaired boot light switch and reinstalled boot light bulbs, “bulb out” indicator illuminated when headlights or parking lights were activated, but now remains illuminated until headlights or parking lights are turned off.
Any ideas?
Thank you.
Charles

 

The bulb out gizmos for the rear side lights are in the boot VERY close to the boot light units, tucked up under the boot side lip. Perhaps you have inadvertently left a connector undone or somehow otherwise caused it to stop working when you did the job on the bulbs. Maybe take a look in that area and check it out?

 

There is another bulb out module under the centre console lid, accessible by removing the ski slope. I've seen them fail a couple times. I'll admit, I don't know how it works and I don't know how it fails, but both times replacing it resolved the same issue. If I had to guess it's probably a relay that turns the bulb out light on when it senses an open circuit. It looks like this:

 

That is the brake light out unit.

 

Ah yes that would make sense as my issue was the bulb out indicator coming on when all the brake bulbs were functioning. Just recalled that- it was years ago.