LCGB Forums

Hello all. As the title says, when I press the horn on my ‘65 Li Special, both the rear and front lights go out. It’s a non battery model. Any ideas please??

I would say you have a bad earth somewhere have you checked anything yet ?

No I haven’t. I’m thinking of taking the headset off on Sunday and hoping there’s something obvious!

I would see if anything’s popped out or touching anything

Will do. Cheers. Just checking for the Mot and noticed it

Do the lights go completely out or just dimmer ?

Horns do pull a lot of current and will dim the lights on batteryless setups.
If it's killing the lights and not actually sounding off, then the horn is, in effect, creating a short circuit.
Are you certain that the horn is one for an AC model? ( if you are unsure, then just connect it across a 12V battery to find out)
Try a substitute horn!

Toddy wrote:Do the lights go completely out or just dimmer ?

They go completely out

Fast n Furious wrote:Horns do pull a lot of current and will dim the lights on batteryless setups.
If it's killing the lights and not actually sounding off, then the horn is, in effect, creating a short circuit.
Are you certain that the horn is one for an AC model? ( if you are unsure, then just connect it across a 12V battery to find out)
Try a substitute horn!

It’s the original horn and switch and the lights go completely out

I’ve had a look at my wiring. Sorry, I was wrong in my initial post, the lights don’t go completely out they dim quite a bit. I cannot see any breaks and the earths look ok. When I press the horn, the headlamp dims and the back light is almost out. The headlamp is a Jockeys one and I disconnected that to see if that was the issue but the rear lamp still dimmed.

Does the horn work when the lights are switched off?

Fast n Furious wrote:Does the horn work when the lights are switched off?

Yes it does

It's normal for the lights to dim when using the horn on an AC setup, especially at low revs.