Hi L.Lynn,
Once again thank you for your email and your always helpful comments. I have changed out the 50 amp in-line fuse above the battery. I agree with your comment about the new fan motors, they may be pulling more
current than the OEM fan motors did, time to measure the amperage. I ordered several extra 50a fuses from XKs Unlimited as most people I have spoken with have discovered that fuse to be blown.
Many thanks again for your contribution. Onward and upward.
Cheers!
Mark Short
Hi Harvey,
Mark Short here from Jag lovers website. I still have a horn issue with my Series III 1974 E-Type which I have yet to solve. I finally located the horn relay, behind the battery on the passenger side. Three
other locations had been suggested by club members, and finally the shop manual. The shop manual was correct, but almost impossible to access!
I have ordered a new relay from XK’s Unlimited, but in the interim I have traced the wires one by one to their sources, cleaning the horn button push, cleaning both horns and confirming they work, replacing
both fuses in #7 fuse location behind the in-dash gauge panel. The 50 amp in-line fuse has been replaced, so here we are at the relay. I have checked brown wire power, perfect, then green wire (fuse #7) and no power, even though I replaced both fuses. Finally
I checked condition of the relay, and all I hear is the “click” but no evidence of current flowing.
What do you think? Is it the relay?
Thanks for your time, always most grateful.
Jagguy Mark
It’s really quite simple.
There are two circuits
The first circuit powers the relay
The second circuit then powers the horn
The first circuit uses a green wire to provide 12v to the relay and a purple/black wire to ground the relay winding through the horn push
(The green wire is a fused white wire; the wire is an ignition switch fed brown wire.)
The second circuit is another different fused brown wire into the relay (fuse on the rh frame rail) and if the relay fires, this continues the 12v via a purple/yellow wire to the horns, which are then grounded to the picture frame by a black wire. To complete the circuit, there is a ground strap above the rh bonnet catch on the frame to the bulkhead and the big thick battery black wire bolts onto the bulkhead close by.
You have two tasks:-
1/ check relay function
Lucas relays work when w1 and w2 have 12v applied across them (for relays without a w2, use c2 for w2). When you do this, c2 and c1 connect. With the relay disconnected, try this test and measure the
resistance between c2 and c1. It should be open circuit if the relay doesn’t have 12v across w1 to w2. It should be zero ohms when you have 12v across w1 to w2.
2/ With the battery disconnected, measure the resistance of all of the jumps outlined in the two circuits. It should always be ~zero ohms. It may be a simple lack of grounding (i.e. a high resistance) because the black wire doesn’t return to the battery negative properly or there may be a high resistance because the fuse holder is faulty or a connector may be corroded.
kind regards
Marek
EDIT :- you seem to be describing a fault on the green wire. check you have continuity (zero ohms) from the fuse board green wires to the green wire at the horn relay. (Do that with the battery disconnected or ignition turned off.)
I can’t argue with what Marek said 
MarekH,
Your email was most helpful in sorting thru our electrical issues concerning the horns. Thank you so much for taking the time to send over this information. I will be back under the bonnet tomorrow to go thru
all of your suggestions, step by step. Excellent explanation of the entire process. I will return with the results of my testing.
Thanks again,
Jagguy 74 Mark
Dear Mark,
A couple of points to consider:-
1/ the horns have a very low resistance themselves, so pull a lot of current when they sound. This is why they are activated by a relay, to protect the rest of the car from high currents in the wiring through the ignition switch and everywhere else along the path the current takes. This also means that any build up of corrosion on connectors is quite significant as that splits the available power between the horns and harnress, which is why I pointed you to look and clean all along the circuit.
2/ Your post suggested that there was no 12v on the green wire at the relay. This means the relay won’t ever fire even though you are grounding the other half of the first circuit through the horn push. If there is no 12v on other green wires from the same source, then you have a common problem to solve. If it is just that wire, then it is either a broken connector/corroded connector or frayed wire.
If this is the case, and you can’t repair the green wire so as to supply 12v to the relay winding, then a workaround would be to disconnect the green wire and supply the relay winding using the brown wire in its place. This means the horns will be available to be used anytime, rather than just when the key is in the ignition. Not ideal, but not a disaster. The easiest way to implement that is to use a Lucas relay with no W2 contact, i.e. only W1, C1, C2 contacts where the brown wire would go to C2, purple/yellow to C1 and horn push W1 via purple/black.
There is a full s3 wiring diagram on the xkedata.com website.
kind regards
Marek
Good morning Marek,
This is more information than I ever dreamed available. Thank you so much for your time and effort to send it over. Later today I will be back in the engine room with more on the horn saga.
Thanks again for your immense information and help.
Much appreciated.
Jagguy74 Mark
Interested in all comments here and the outcome. My 1971 Series 3 2+2 horns work just fine, but it’s with a separate button under the dash added by a previous owner. My question is how to get the steering wheel button to work. Do I run the horn wires up inside the steering column and connect them to the steering wheel horn button terminals? Seems there might be a brass shaft running down inside the steering column to a switch at the bottom. Having trouble getting the true arrangement.
Dear Fenner,
The steering column rotates, so the wire from the relay winding will have to mate with an insulated connector which will have a slipring connection onto the rotatable steering column. From there a brass rod will make a metl to metal connection to the chassis through the remainder of the steering column.
Your extra switch will be there because the slip ring connection isn’t working so you can never earth the wire coming from the relay winding by “pushing the chassis connection onto the slip ring”. Look for an insulated female bullet connector on the steering column and a brass-brass slip ring contact underneath it.
kind regards
Marek
My experience is with my 67 but as Marek describes, there is an electrically insulated “wiper” that rests on the brass rod, providing a connection electrically that also allows the steering wheel to rotate. The arrangement is not robust! If I recall, one of the parts vendors sells a kit with the items one would typically need to get the connection working again. You can test it by pulling the steering wheel, exposing the metal rod, and using a wire to momentarily connect the rod to ground. If your horn sounds, you are in luck. The problem may only reside with the center push button on your steering wheel, which is much less complicated.
Of course, as the original poster has discovered, there are many ways and places for the horn system to fail. Ultimately, you need to troubleshoot everything to find your problem.
I am just beginning the process of tracking down horn issues on my '72 S3. I am rebuilding the car following a bare metal restoration. The horn relay is good but not being tripped with horn button. I will try grounding the push rod to see what happens. I see several purple/black wires in the area. One of the PB wires is attached to the spring contact under the steering column and is cut, another is coming from the ignition switch, and another is coming from the wire harness near the ignition switch. Wiring diagram shows PB wire to the horn button and then to ground. Where is the horn button grounded? Where is the cut PB wire supposed to go?
The top of the ignition switch is part of the seatbelt warning system - see the s3 wiring diagram and grounds one of its connections when the key is inserted.
The horn push connects to the chassis when pushed. (The chassis is connected to the battery negative.) The other end of the horn push connects via a rod down its centre to a slip ring on the column. That then connects to the wire that grounds the horn relay.
I’ve no idea where your cut wire comes from or goes to, so with the battery disconnected, use a meter to check continuity of wires you don’t understand where they go.
kind regards
Marek
Great reply! Thanks. Back to the investigation in a couple of days.
You ought to be able to see which way in the loom the wires go. I’d suspect that the “cut” wire is maybe simply missing its bullet connector and is part of the slip ring connection. One of the purple/black wires has to be the one coming from the relay and that’s the one you want to ground to make the horn sound.
The other arrangement used the indicator stalk so check out that connector also.
kind regards
Marek
Hi All,
I am happy to report that I was able to locate my horn issue, and now the horns work perfectly. The culprit was the relay fastened to the inside passenger fender wall right behind the A/C dryer unit. It was a pain in the po-po to reach,
and poorly fastened to the sheet metal (hanging by a single bolt and nut). When removed, it was revealed that water had found its way into the relay and damaged the inner workings, leaving a nasty blue residue around the edge of the unit, and all posts distressed.
Once the new relay was in place the horns worked perfectly. Once again many thanks to all who offered assistance; I followed all suggestions, locations, and items to be cleaned and/or replaced, ending with functioning horns.
The next chore at hand is to properly fix the fan motors so this poor beautiful cat never over-heats again. This year it was particularly stressful as it happened on the show field as I was attempting to place her for competition. It has
new aluminum fans and a new radiator installed. You would think all of our issues are gone, but not so. First issue, the fans are not coming on AT ANY TEMPERATURE. I shall replace the temp. valve first, replace the fluid, and continue onto second problem.
As I proceed I will report my progress.
Many thanks,
Mark
We’re you able to sort out the radiator fan problems?
[https://forums.jag-lovers.com/user_avatar/forums.jag-lovers.com/872xke/45/1017_2.png]
872XKEhttps://forums.jag-lovers.com/u/872xke Joe Frazierhttps://forums.jag-lovers.com/u/872xke
September 21
We’re you able to sort out the radiator fan problems?
Hi Joe,
I have been out of town for 4 days, however tonight I am back on the “fan” case. First job will be to raise the car and drain the antifreeze, then replace the temperature sensor. This is a new aluminum radiator with new high-output fans. This is NO reason why this car should be running hot. One of our engineer members felt like one huge problem is the radiator cap not sealing properly. He secured a round seal ring from the hardware store, placed it in the neck of the radiator, replaced the cap, and the “boiling over” stopped. The cap only extends into the neck ¾” whereas it should be a 1” cap. The 50 amp fuse was blown which probably explains why the fans were not on. (That has been replaced). Our mechanic has already replaced the relay, so a check of the wiring route will commence after the car is drained.
I believe the system should always have one fan on, and when the temperature sensor exceeds 160 degrees the second fan should come on, isn’t that correct? Please advise if this isn’t the correct modus-operandi. Many thanks as always for your assistance.
Mark
My fans operated together, both on or both off.
I am having similar fan/horn issues. I am in the process or replacing relays and switches, so keep us posted on how you progress. Thanks!
Absolutely. First job will be to drain radiator and replace temperature sensor in hose connector at the bottom of the radiator. More to follow.
Dropguy
