Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Horn not working 2013 Plus 4

Hi All, would appreciate some advice. Horn has stopped working I have thus far -
Removed horn and tested, it works ok.
Changed a plethora of fuses in the cockpit fuse box having looked at all of the online fuse diagrams. Everything else on the car still woks.
Removed steering wheel and cleaned all electrical contacts.
Horn push contact looks ok.

Not sure what to do next .I wondered if the system has a relay am unaware of ?
Any thoughts would be appreciated
Regards
George

It's marginal at best. See what rated fuse is fitted. Try going up 5amp. Also test with the engine running!

There may be an added relay. The MMC horns fail & I fitted better ones with a relay. How is the earth from the horn push? Csan you take the power to the horn push & run a test wire to another earth to test it?
Some cars had 2 horns.

Do not take any power to the horn push. It simply completes a ground return to the live horn when ignition switch in accessory or run position. This is a unique feed from ignition switch on a light green/white cable running to 10 amp fuse 9 and on to both horn and switched radio feed. If you don't have a radio you may not have noticed this feed has failed. There is no relay involved ex factory. With ignition switch in either of above positions check for presence of +12 volts with multimeter on light green/white cable at ignition switch, each side of fuse 9 then at horn itself all on same colour cable. Note the wiring loom caters for two horns, although I believe only one fitted on Plus 4. Do not reduce fuse 9 to 5 amp!

The horn push switched ground return runs back from horn on purple/black cable to horn push slip ring. No harm in dabbing a grounded test lead on this horn contact to check function with ignition switched accordingly. A very thin smear of dielectric grease on horn push slip ring will do no harm if you trace fault back here although you mention you have already checked.

I have recently replaced my steering wheel. The horn slip ring was not in good condition, the lube had gone very hard, it needed a good clean & re-application of electrical contact grease. Whilst it was still working I don't think it would have for much longer.

Thank you all, I cleaned the slip ring as it was somewhat dirty and crusty, however did not apply new grease . Thanks for the tip.

Did that fix the issue George ?

BTW people have queried the use of dielectric (insulating) grease to lubricate a sliding contact. Its a case of the lesser of two evils though as you wouldn't want an excess of normal (conducting) grease allowing a current leakage path from slip ring to ground. On the other hand the sprung contact leaves such a thin layer of dielectric grease between it and slip ring, it makes negligible difference to the horns current draw.

I use this stuff. Seems to work well

Hi Richard,
Thanks for the advice , currently away for a week will let you know how I get on in due course.
George

Unfortunately that's not the ideal. Conductive grease (as many are) can allow current leakage if it spreads from slip ring to nearby electrical ground!

It may seem counter intuitive to use dielectric grease but in this situation its proven the wiping action between sprung contact and slip ring leaves such a thin layer it has near zero impact on conductivity of the horn circuit as already mentioned. This also allows it to be used safely on the contact pins of plug in relays if in relatively exposed positions, to minimise contact corrosion without any leakage between, as well as easing their replacement.