Horn not working when main lights are on.

As the title says - I've got this problem, horn works when side lights are on, and all lights off, but put mains or full and its silent.

Cant figure out how or why!

I think you need to spend a bit of time cleaning all you connections and earths in your car.

A bit of TLC sounds like it would not go amiss. They do got a bit crusty over time.

Are your lights a bit dim when you turn them on?

Cheers

Also ,

You say "they" fixed your horn in your previous post, who are "they" and what did they do to fix it?

Cheers

sorry the they is the horn!
I fixed it by cleaning terminals and snipping the end 3cm off the wire and putting a new end on it.

And as you say it - the lights are a little bit dim for my liking, id say 70% of how bright they were originally - Im hoping this is a clue?
If its an earthing issue, is their an area I need to start at and work back from - IE a main / most likely culprit?

For earths, any I've come to so far have been wire brushed down, but as of yet I've not found any that are badly corroded.

Dcoximus said:

And as you say it - the lights are a little bit dim for my liking, id say 70% of how bright they were originally - Im hoping this is a clue?
If its an earthing issue, is their an area I need to start at and work back from - IE a main / most likely culprit?

For earths, any I've come to so far have been wire brushed down, but as of yet I've not found any that are badly corroded.

Click to expand...

When you say wire brushed down, do you mean you have taken the bolt out, wire brushed the earth cable surface that touches the chassis and wire brushed the chassis where the cable will bolt to? Wire brushing the top of the earth point will not achieve a great deal.
Are you testing the horn with the engine running?
Does the engine turn over quickly when you start it or does it turn over lethargically?
With the engine running, do the lights get a lot brighter when you rev the engine?

I take the whole lot out and wire brush everything - bolt, body, and cable until its clean.

The lights dont get brighter if I rev the engine and the engine starts fine, within a second - however if the lights are on it is sluggish and wont always catch.

And thanks to everyone on the reminder for earthing - found some badly coroded earths in engine compt on front of bulkhead and one near the wiper motor and cleaned them up, everything started working. Going to go through all the other earths I can find and give them the treatment.