Hi All, I have recently got my 1 owner XJ6 on the road and am happy to say she runs great and everything works… except the horn! If we’re being technical, neither does the alarm, but I haven’t found that yet!!
After a bit of fiddling, I found that the two horns were not connected and the wires for doing so, were dangling right there… A very convenient fix… except of course things are never that easy.
Once the horns are connected, when I attempt to start the car, she won’t turn over and the horns just wail as if the alarm were set and tripped. When I disconnect the horns, everything else works as it should.
Crazy thing is, I can’t find the alarm system. I assume that the easiest fix is to disconnect and remove that… you know, if it wasn’t so stealthy hidden.
Anyone have any suggestions on where the systems were attached? This seems to be a pretty high end install, but I’m just guessing due to the information I have on hand. Any insights greatly appreciated.
Minor detail, but I’m selling the car and want to fix as much as I can before listing.
Phillip,
No Series III saloon left the Jaguar factory with a security alarm installed. So you are dealing with an aftermarket installation of unknown origin. If you post some pictures of the alarm equipment others may be able to help.
Thanks Paul. I’m certain the alarm is aftermarket, I just can’t find it! Was much easier in the E-Type. The only tell tale signs that there was an alarm are the red light indicators on the door sills.
I’m going off what the original owner told me. I can tell you this, aside from the horn blaring constantly, I couldn’t keep the vehicle running when they were connected. The oxygen sensor light would come on and the car would just die after a second or two.
Maybe it isn’t the alarm… maybe there’s some other short somewhere. All I know is that it originates with the horns being connected.
Phillip,
To find the aftermarket alarm equipment you will have to think like an aftermarket alarm system installer. Where would he put it? Why under the dash on the driver’s side near the fuse box and ignition switch where he needs to hook up his equipment.
It’s possibly an alarm system feature, Philip. The alarm system, armed, prevents cranking, and uses the horn as thief warning/repellant - a common feature. Somehow; disconnecting the horns ‘disarms’ the alarm system - which would be most unusual.
Most alarm systems have a ‘hidden’ override feature - allowing the driver to disarm/turn off the alarm. The trick is to find it - and it might, somehow unusually, be associated with the horn circuit. Cannot really advice on that; the alarm type, and then features installed, depends on locating the ‘black box’. And the whim of the installer would require tracing wire colours and comparing it to the car wiring…
As the car operates OK with the horns disconnected; there is no hurry. Except that the alarm system does not work(?) - which most of us make do without.
For some elimination purposes; with the horns connected; do they ‘blare’ as ign is turned ‘on’ - or only if the ign key to ‘crank’? In the latter case it’s likely part of the alarm feature - in the first case; it may be related to a short in the horn circuit…
As anyone dealing with (aftermarket, known or unknow) systems knows; sorting it is an uphill battle - and possible faults in the system adds to problems…
Thanks Frank, it’s definitely the latter, and while I have no desire to use the alarm, not having a horn in Los Angeles is treacherous! I have found what I think to be the override button, so that will be the starting point for my next foray behind the dash!
Indeed, Philip - alarm systems generally have an ‘on/off’ function; not everybody wants it on at all times.
But my 89 Toyota have a ‘crank inhibit’ ‘alarm’ function, with a fob with a button, like modern cars - only it arms automatically as the ign is turned off. Required ‘push the button’ each time for cranking…
With only one fob for two drivers, no extra available (Japanese used import - ‘alarm’ fitted in Japan.), I looked for solutions. I found a dangling wire with a tiny spring loaded button which I taped ‘in’. What’s yours…?
Look at the horn relay. It should have 4 wires green (from ign key/fuse #11), purple/black (to horn button/ground), brown/purple (permanent power, from inline fuse) and purple/yellow (to horns).
Unless you find more wires at the relay; I suspect that brown/purple is connected through the alarm ‘black box’ - to sound the horn when alarm is ‘on’ and triggered. With horns disconnected, the alarm is either inactive, ‘off’ or simply faulty.
There is another/further possibility for the horn ‘problem’. the purple/yellow is connected to a ‘finger’ to an insulated slipring on the steering wheel shaft - connecting the relay to the horn button, via a complex set-up, giving relay ground when the horn button is pressed. If there is a short in this set-up; the horn will sound when ign is ‘on’. Disconnect purple/black from the slipring ‘finger’ - and ohm finger to ground. You should read break (‘1’) - if make (‘0’); you have a horn problem, separate from the alarm issue. Some different action is then required…
It’s a bit complicated; if the (connected) horns is silent with ign ‘on’, but sound when horn button is pushed - it’s an exclusive ‘alarm’ issue. If horns sound with ign ‘on’; measure ohms as described as an initial step. The question is if the ‘alarm’ is triggered when ign key is turned ‘on’ - or some other way…
Of course, if your override button restores normal function; car cranks and horn only sounds when horn button is pushed - all is well. You have ‘solved’ the problem, having both alarm and horn function…
But there should be an ‘on/off’ switch/button somewhere - and it might be your override switch…
Frank, this is immensely helpful. Yesterday I tried to connect the horns again. This time, they didn’t go off, but I couldn’t start the car to save my life. It would crank, but wouldn’t catch. All the electrical worked, but I did notice that while all the gauges were activating while cranking, the volt gauge didn’t.
I gave up and disconnected the horns and the same result. Scratched my head and tinkered for a couple of hours but couldn’t fix it.
I looked under the hood to see if I could find the kill switch or anything that looked out of place. The only thing I noticed was the wires connected to the coil were very brittle and one in particular was connected loosely to another. (The casings on all were cracked and gappy). When I lightly tugged on the wire it broke in my hand. I was fortunate that it was long enough for me to strip a new piece and I wedged it into the connector on the wire it was previously connected to. Low and behold, the car fired right up.
I’m not sure if it’s two separate issues, but I’m working up the courage to try the horns again tomorrow!
I did learn, through searching through the service records, that it once had an alarm system called “Derringer.” I also learned that it was subsequently removed at a later point so I don’t feel as silly for not being able to find! Onward and upward!
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…I’m not sure if it’s two separate issues, but I’m working up the courage to try the horns again tomorrow!
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Indeed, Philip; your symptoms are perfectly explicable with three (or more) faults appearing simultaneously and possibly intermittently. It’s just that we seldom encounter such coincidences - and we just have to mend what we find wrong, one thing at a time…
The failed coil wire will of course not prevent cranking, only starting - and the relationship between horn wires and ‘no crank’ remains mysterious. Which, with an aftermarket alarm system, makes that a prime suspect. Even if removed; the removal of it may leave unknown ‘residue’ if improperly done - hence more testing is required…
The ‘Derringer’ alarm is unknown to me, and may not exist anymore - so sorting it’s sensors and intended actions ‘difficult’. However, clarifying if horns work as intended when connected is a step on the road…
Where would he put it? Why under the dash on the driver’s side near the fuse box and ignition switch where he needs to hook up his equipment. 
