Hello, a new member, just found the forum while searching for info on the horns, read a great post regarding it from here but my problem is slightly different. As this forum looked to be active, thought I'd join.

The car is a 1985 V12 Coupe, I am not sure if the horn has ever worked in the short time I've had the car but it must have a few weeks ago as it passed the MOT! Right, press horn, nothing happens, checked all the fuses - fine and other stuff on fuse 11 works perfectly. So then with the bonnet up, when I press the horn, I can hear the relay clicking away happily. I checked the horns themselves and with 12volts to them, they work a treat (loud!) also, with 12 volts fed down the wire from the relay to the horns (separate source) the horns again work. So, I surmise that the wiring to the relay is working and the wiring from the relay to the horn is working, but no horn! I did grab another 4 pin relay and that also just clicked with no firing of horns.

I am not the worlds greatest when it comes to electrics, in fact, I can get confused wiring a plug but I have a multi-meter and a power-pack so can blow up most things! ANy ideas chaps/chapesses?

 

its best to be systematic about electrical diagnosis. Put your meter at the horn terminals and check voltage and work your way back until you find out the space where you do and do not have power to locate the problem.

I could be missing something, but it sounds like you take the relay clicking as working, but didn't actually check to see if it is closing the connection. You also make is sound as though you checked voltage to one side of the relay, but perhaps not the other, so my guess is the relay isn't working or the feed to the horn side of the relay doesn't have 12v.

 

Thank you for the response, I shall check tomorrow. But I also seem to have a less than steady supply on the constant 12 volt, sometimes as low as 2.5 volts! Is there a separate fuse for this feed?

 

The horn relay is under the plastic cover, inside the engine bay, behind the LHS headlight nacelle. There are three there and the horn relay is/should be the black one. The top one is the headlights and the red round one is the auxiliary fan.
Unmarked on all jaguar documentation is the fact that the horn circuit has TWO fuses. The fuse you have checked, and also the fuse in the engine bay, inner LHS wing, under a plastic cover, front-most fuse. This is marked as the auxiliary fan relay, but it also does the horns. Check that, replace the fuse and clean up the contacts.

 

Check the other horn fuse that's under the hood located on the left inner fender well. There are 2 fuse boxes right together, one with a white cover and one with a black cover. Fuse #6 under the black fuse cover has a brown wire that is the 12 volt high current source for the horns themselves, turned on by the horn relay itself. On my '88 XJS, fuse #6 under the black cover is the fuse closest to the firewall. ..........Mike.

 

Thanks guys, I will check all these points. Seems odd that everything works, but the horn doesn't!

 

Yay! Horn now working! Seems to have a been a bad connection, fuse or the wires that go to the relay, not sure as I just cleaned them all *****-nilly. Topped up the coolant (after thermostats were changed) and slowed the idle speed back to 750 when warmed up. Bit difficult as the gauges are in a state of 'approximation' rather than actual but the gauge was off the stop which is about as high as it ever gets!

Clocks next but I may just clean the car after its mammoth session of being 'fiddled with' and do the unthinkable: use it!

Oh yes, also made good use of the previous post on this problem by 'Greg in France' which helped loads