Attempting to fix horn wiring

Finally got around to ordering my new Moto Lita wheel, which is gorgeous by the way.

But now I’m trying to solve my horn wiring, which has never worked. I pulled apart the wiring looms under the dash, it seems one goes into the column shifter and feeds the side turn light indicators and the turn indicator lever, then there’s another loom that sort of disappears behind the indicator switch. There are about 6 wiring coming out of that loom, which I tested each one by putting a hot wiring on it, then putting a test light on the spring loaded horn push at the steering wheel. None of them lit up the test light. (I also tried pushing the horn button all the way down wondering if it would only show power depressed). No luck. I cannot find any other wires coming out of the steering column. Am I hunting in the right place or is there a horn wire hiding somewhere else?
Thanks

On my XK150 the horn wire is a grounding wire. One side of the horn is
connected directly to power. The other side of the horn is connected to
the wire going to the steering wheel push button. When you push the horn
button, it grounds the wire to the steering frame.

Theo,

If you look down along the steering column, about 6 inches from the firewall you will find a single wire, this is the wire that the horn pushbutton earths.

Here is a pic of that part of the steering column:

EDIT: changed the photo to include highlighting the connector.

Andrew - thanks for the picture. The wire exists at the first opening closest to the top (left) or the further opening down more (right)? And it exits and hands with a connector at the end I assume? I’ll check again. Perhaps this wire has disappeared…

Theo,

I’ve added some highlighting to the photo.

On some of the other cars, there is a long slim rod that connects the horn button to the internal contact within the steering column, which is a copper plate and spring arrangement.

This internal copper plate that acts as the earth connector becomes displaced, so no connection can happen.

There is repair methods described in a couple of archive posts I have read

My 420G horn does not work except via a PO fitted bypass horn button
(on the to do list)

there is “horn fix kit” available with all the bits from the major Jag suppliers

As long as we’re on to horn wiring in the steering column my 3.8S horn works fine if I have the steering wheel adjusted closest to me. If I adjust the wheel closer to the dash the horn blows continually. Since I always have the column pulled out fully this has not been an issue but it would be nice to correct sometime. Any ideas what I need to look for and repair?

Hi John, just rebuilt my 3.4S steering column because the horn would blow every time I put any pressure on the wheel. Turns out it was the total disintegration of the two insulating bearings in the column causing a short to ground. Interesting experience and I got to know the column assembly quite well; there are quite a few bits involved. There is an insulated wire running through the hollow upper .steering shaft from the spring loaded horn button behind the centre cap to the copper connector shown and highlighted above in Andrews photo. This wire, (18" long approx) is almost taut when the wheel column is extended, ie. wheel closest to the driver,and goes slack when the column is shortened, ie. closer to the dash. You probably either have worn insulation on that wire or, there is a short at the the connector to column at the previously mentioned copper connector in the photo. You can check this without taking the column out if you are a contortionist.There is also a “top hat” insulator that keeps the spring loaded horn button away from the column ground behind the horn centre cap that looks like it could be compromised over time but in mine was ok for reuse - this might be the easiest to check first. Mines a RHD MOD with +ve earth and the column was quite easy to remove and replace (after 3 or 4 times), not sure on ease with LHD or auto if that’s what you have. Usual electrical troubleshooting approach works.
Good luck.
Peter

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Thanks for your detailed response. A number of years ago I did replace the white nylon bushings, upper and lower, and at that time I had the whole column assembly out. Your description seems to lead me to think the 18 " wire has worn its insulation off and shorts out when the wheel is in other than fully extended position. Sounds like a summer project to remove the column again and check and or replace this wire. Mines a LHD MOD (negative earth but that makes no difference) car so no auto gearbox linkage to deal with.

John Quilter
Eugene, Oregon USA

I have been trying for a long time on my MKI to find the wire that attaches to this gadget on the steering column. Does anyone know where this wire goes though the firewall to the column or does it come in with that big wire bundle on the right-hand side of the cabin and then run to the left (on my left-hand drive car) high along the inside of the dash to drop down somewhere?

I don’t know the Mark 1 at all, but if it is anything like the other saloons then the wire will pass through the firewall as part of the main harness.

According to the Schematic the wire should be Green/Black.