Morris Minor Owners Club

Failed MOT on a bit of known chassis rot but also on horn. Not a peep but tested the circuit and 12v is getting to the horn when the button is activated. So, I got a new double-horn set and a 40A 12V relay (pins 85 86 87 87a 30) from maplins. Got it home and see that it is SPCO but was convinced that it was described as SPDT in shop. However, it looks like the difference is that it has an 87a terminal while the SPDT does not. I decided to test out the circuit by wiring up to a battery out of the car. I have followed the diagram that I have uploaded and have had no luck in getting any sound from the horn. When I connect/disconnect the live side from contact 30/85 you can hear the relay click on/off. I have read that you can reverse the wires to contacts 85 & 86 as the diode may only work one way but that doesn't make a difference. Any advice before I get the re-test onb Thursday would be appreciated. I do have another spare horn and another relay but nothing is working for me.

One question - can I just put 12v direct from the battery to the +/- on the horn to test if it generates a sound?

Thanks[frame][/frame]

PS: Just did a bit more searching. I am using one of those 12V yellow charger/jump starter to provide power to my test circuit. Could this be inhibiting the horns from makng a sound? Should I just use a battery?

You seem to have it wired correctly. I don't see why you have gone to this trouble to cure a failed horn.
The horn can be tested directly on a battery but beware, it will make you jump!!
In a standard setup the battery was always connected to the horn and then the horn button just earthed to complete the circuit.
You need to confirm that your horn button is earthing before you go to the trouble of adding the relay.

Thanks for comments, Beero. Agree that I have over-complicated things with the relay so have backed off that, installed new horns and, apart from a dodgy connection around the fuse box, the dB from the horns are much improved.

Cheers

That will be handy when BMWs are hogging the fast lane and you want to give them a blast to move over!!!

Well it is a 1275 lump, but I still can't find fifth and with no motorways in Dorset I have fitted a speed restrictor!