Horn works with ignition switched off but not when switched on?

[Jagman42]

I have a problem where the horn works fine when the ignition is off but not when turned on. Have changed the relay( 6RA) as assumed this was faulty and done the checks with test lights as per Haynes manual and also Jaguar service manual, but still not working.
Original horns have been replaced in the past by set of airhorns and the car has an additional 4 pin relay fitted of 30amp next to standard relay 6RA that was originally on the car( this has also been changed to see if this was at fault but would appear not to be).
In the factory service manual under the appendix for Series 2 cars it still shows 3 relays. The horn the alternator and ignition / plus the AC if you have it. I seem to have only the 6RA relay, plus the 4 pin square relay as mentioned above.
I have read (somewhere) that Jaguar dropped the alternator/ignition relay? Is this correct??

MOT due soon so any help as to why I am unable to get it working or suggestions would be most welcome.
Thanks in advance

[Heuer]

Should be fairly simple to test. First disconnect the horns. If that 30amp relay is for the horns then that is where you should start. With the ignition on operate the horn button and you should hear a click from the relay. With the ignition off there should be no click. The relay coil is simply earthed through the button so you want 12v on one side with the ignition on (pins 85 and 86 if it is a modern relay) and nothing with the ignition off. If not you need to correct the situation.

Once you have the relay clicking to command you need to check if there is 12v on one of the other two relay terminals (pins 30 & 87) with ignition on and off. You want 12v with ignition on, if not you need to correct it. Finally connect the horns and test.

[Jagman42]

Thanks for the quick response,certainly drier inside the garage than out!
Will go through it again asap and see if it solves the problem. Assume that i only need the 2 relays is correct and Jaguar workshop manual is wrong??
Will let you know how it progresses, appreciate your help, but coming round to the fact that the replacement main relay that I fitted may have been faulty so will follow you advice and if it still does not work will go for a replacement unit.
Thanks again

[chrisvine]

I don't think any of the relays were deleted later on in the production run. A previous owner may have upgraded the alternator which could result in this relay being unnecessary.

Assuming you don't have A/C, there should be two relays on the mudguard - the horn and alternator. The starter solenoid relay is either in the cabin under the RH A-post or on the RH bulkhead in the engine bay for later S2 cars.

[Jagman42]

What I thought was the alternator relay turns out to be the horn relay. The problem is that in the past the car was fully dismantled for a full respray but some of the various parts/wiring etc whilst being put back are not in the correct place so difficult to follow using the manuel. Also it really needs a rewire as paint from the respray has masked some of the wiring making identification difficult.
Anyhow the horn relay (SRB111) seems to be correctly wired in according to the wiring diagram that I have.
W1 Green
C2 Brown/Purple
C1 Purple/Yellow
W2 Purple /Black.
Will now check as per your response to see if I can identify the problem.

This leaves me with the more modern relay 30A which would therefore seem to be wired into the alternator. I was planning to change this for an original Lucas unit ( SRB121?)

My chassis number is in the IR1160 area,question is am i going for the correct alternator relay as different dealers have different model numbers.
Mine is a UK car so on AC etc.
Await your thoughts
Thanks

[Heuer]

You should have 12v on C2 with ign on. Try shorting C1 and C2 which should sound the horns.

[Jagman42]

Tried shorting out and nothing happening?
Should i be looking elsewhere?

[Heuer]

Please confirm you have 12v on C1 or C2.

[Jagman42]

Thanks for response been out today but just checked and have 12V on C2.
Nothing on C1
Await response, but thanks for your patience, I am no wiring expert as you can see but it would have helped if bits had been put back in the right place during the respray!

[Heuer]

If you have 12v on C2 (ign on) and you have shorted C1 and C2 then there is a problem between C1 and the horns which is odd because you said the horns operate with ign off:


Do you have 12v at W1?

Next test is to remove the lead from W2 and connect it (W2) to earth with a jump lead. Relay should click and activate the horns. Basically the two W connectors are for the relay winding. When 12v flows by pushing the horn push (connects to earth) the relay contacts C1 and C2 close allowing current to flow to the horns.

[MarekH]

To verify the main power wiring:-
With the ignition on or off, momentarily touch the brown C2 wire to the purple/yellow C1 wire. The horn should sound.

Make sure you are using a relay which has both of the W1 and W2 connections clearly marked on the base of the relay. (Some Lucas relays only have a W1 - they have no W2.)

To verify the correct working of the relay:-
Connect up the W1, C1 and C2 of the relay as per your post #5 earlier in the thread but leave W2 unconnected.

Verify that with the ignition on, you have 12v on the green wire on W1

With the ignition off, momentarily earth the relay's W2 contact directly to a known good earth like the battery negative terminal post (or the chassis) and report back - (I am expecting that the horns will not sound).

With the ignition on, momentarily earth the W2 contact directly to the chassis and report back - (I am expecting that you will be deafened).

If you pass these tests then your problem lies with the earthing connection to the w2 terminal, so......


Please also let us know whether your car has its horn operation via the horn push or via the turn signal stalk.

If it is the latter and the relay was originally correctly wired, then it may imply that stalk has a fault, as that may explain how the horn can be made to sound with the ignition off. If this is the case then I can describe a further test to verify that.

kind regards
Marek

[Jagman42]

Thanks for all the help and apologies for the delay in responding.After following all the advice etc it turned out that even though the wiring for the horn had been routed via an alternative switch connections were incorrect. After a bit of training on using a multimeter the problem has been solved and have now disposed of one of the wires altogether!
Pleased to say that it has now passed the MOT today so all is well!
I now really need to get the car rewired as existing loom has faded ( and covering rotted) so very difficult to follow the wiring plan for any future problems.
Learning slowly!
Thanks again