Possible earth fault?

[pg42]

Hey chaps, urgently need some help. I have a 1976 Jet 200 just failed MOT because when the horn is pressed, it nearly kills the electrics. The lights dim VERY badly. I fitted a new stator plate, loom, CDI etc etc on a rebuild a couple of years ago. The MOT tester suggested a bad earth but having removed, cleaned and refitted every earth I can find, it is still the same. All sensible suggestions welcome.

[MickYork]

in most cases you take a live directly to the horn then switch the earth wire. yes a bad earth from the switch to earth could be the cause. try touching a piece of wire to a good earth and the earth side of the horn.......if everything works as it should it's a dodgy earth from your switch.

[dickie]

Your symptoms mean that you have excessive volt drop when you use the horn. This is caused by one of 2 things: excessive current through the horn or a high resistance in the feed to the horn and everything else.

Have you tried a new horn?

I can't remember off the top of my head where the horn 12v comes from but I think it's in the headset. My money says your problem is in the headset on the junction where the horn and everything else up front gets their 12v from.

[coaster]

A few thoughts, firstly, the lights will dim if the engine is only ticking over or at relatively low revs, that's completely normal, applying the rear brake will have the same effect.

2nd thought is if the problem exists at higher revs then as well as all the obvious connections, you should also make sure the earth connection on the stator itself is sound. The stator earth is just a tag riveted to the laminates and often work loose especially on Indian stators.

3rd fault is as already mentioned, the horn itself could be faulty.

[pg42]

Thanks very much folks, much appreciated all of your help. Ended up being a knacked horn (after stripping and cleaning all earth connections). Job done!