Series 1 light switch issue

[Leotech]

Wired my series 1 150 today and everything works fine except the horn.

The horn will only work when the lights are switched to off?

Anyone any ideas?

[byron]

how is power getting to the horn ? from a branch out from the loom ? or down from the ignition switch ?
try earthing the other side straight to earth, to eliminate switch issues

[Leotech]

The power comes from the brown wire as it passes the horn. there is a white wire which comes down from the switch.
The horn button seems to put the white to earth when pressed.

[byron]

...The horn button seems to put the white to earth when pressed.

which is how it should be
try earthing the horn terminal that the white wire goes into straight to earth, with the ights on.
if the horn works then problem is likely to be with the switch.
if it still doesn't [but does with the lights off], issue will be with the brown feed, either on the junction board, with the ignition switch [if you have one] or again back at the light switch.
maybe check the light switch is working as it should be with a multimeter
and are the lights bright enough...?

[Leotech]

All the lights seem to work ok. Nice and bright etc.

I'm thinking there is some kind of double supply to the horn, the brown direct to the horn and maybe a purple of grey behind the horn button? Are the switches with different amount of wires on like the series 3?

It's an original series one switch, I had to remove a bit of the housing as some of the soldered joints on the rear were earthing on it. Pretty sure I've had this before on a series one I built about 10 years ago but can't remember.