Horn works intermittently on 72 twin cam

[GPS]

Hey Fellas.
Thanks for the help on the fried red and white ignition wire issue. I am dealing with that now.
Haven't got it resolved but I feel soon.
On another wiring topic.
I have a 72 Twin cam. The horn works for a while after starting. Then it wont work, but when I push the horn button
there is a spike on my amp gauge. Any thoughts on plan of attack?

[BDA]

Do you have the stock horn? If so I'd throw it away and get something that makes a lot of noise! I might try running the horn directly from the battery to see if there is something in it that is causing it to draw a lot of amps. Then I would try to follow the horn wire from the plug for the steering column stalk assy to the horn to check for shorts, frayed wires, poorly crimped connectors, etc.

This page (http://lotus-europa.com/manuals/) has a lot of great information including searchable online manuals, color wiring diagrams, tech data not found in the manuals, useful mods, etc. I think this is your wiring diagram (http://lotus-europa.com/manuals/misc/electrical/tcfedc.gif).

This isn't likely to be your problem but since you're dealing with your wiring, you should know that US fuses are not rated the same as UK fuses (see attached document). You should make sure you have the proper fuses in your car.

I hope that helps!

[Clifton]

I had bad ground. It would drop out with load. I think the book shows a ground strap on the steering shaft. I just used a relay so a poor ground turns the relay on for the proper ground.

[4129R]

The 12v feed to the horn comes from the fuse box, and you sound the horn by earthing the wire from the horn to the chassis.

So check that there is power to the horn when the ignition is on. If the fuse has a bad connection, that may be the fault.

If you have power to the horns all the time (access behind the left headlight bowl) then the problem is with the earth or the horns. European spec cars earth through the centre of the steering wheel, US Federal cars earth through the indicator/dip stalk on the steering column.

Test the horns by earthing the horns with the ignition on using a new wire attached to the horns, and earth it to the chassis.

Classic car horns are cheap and available on eBay. 2 x 1/4 UNF nuts and bolts hold them to the left front wheel arch, so they are covered with mud. Take out the left headlight bowl to see them, and to get a spanner/socket/wrench on to the bolt heads, and for access to the 2 electrical connections.

   

[Kendo]

It's been a while, but as I recall, the horn has a little screw on the back you adjust to make the (weak) sound as loud as possible. If it's misadjusted, I could see it passing current, but not making much sound.

[jbcollier]

The horn is an electrical solenoid attached to a diaphragm and points.  When you complete the circuit with the horn button, power flows through the solenoid’s windings.  This moves the diaphragm and opens the points.  The open points collapse the windings, the diaphragm moves back and the points close.  This repeats rapidly creating the horn’s “honk”.

The adjustment screw controls the amount of spring pressure holding the points closed.  Less tension gives a higher tone (faster on/off cycles) and more a lower tone.  It only works within a narrow range.  In the old days you set it up by adjusting the amp draw but those days are long gone.

You can take the horn apart and clean the points.  Just mark everything so you get it all back together correctly.  Then adjust for the tone you want.