Air Horns power supply?

[au-yt]

My 71 Elan Sprint car is fitted with the "Maserati" air horns option . How ever they don't function as they should from the horn button.and on checking with a volt meter they have no power to them.

I have removed them and did bench test of the compressor and it works very well.

As I have just changed the heater hoses and the radio and glove compartment are out I have started to trace the wiring. using an OHM meter and a probe. I can trace the wire form the column to where it goes into the loom out to the engine bay but it vanishes when its in the engine bay. BUT the wire (no continuity) appears from the end of the loom!
I thought the Italians were bad at this seems lotus mastered it as well.
There are two wires to the horn, purple white and black which I assume is earth.

I have a wiring diagram which is blown up in size but that indicates its one wire.
I am wondering as I write this if the horn power is supplied via a relay the horn button is an earth for the relay and actual power is from another source. The car was retrofitted with a "factory" alternator and I am wondering if the power came from the original regulator does any one else have some insight?

Cheers

Graeme

[mbell]

Your description of how it works is correct. There should be a red 3 terminal relay. With purple power feed, purple black that is the ground via horn button. Purple yellow that goes to the compressor. Then ground connection to the chassis.

[au-yt]

Thank you, I assume that the Sprint wiring is similar to the +2
I will refocus my attention on a dead relay, let you know how I get on.

Cheers
Graeme

[billwill]

There might be a hidden fuse that has blown.

I have various in-line fuses tucked behind the dash, some I can reach by taking the ashtray out.

[alan]

are you sure the earth at the horn push is good and it is not a problem with the earth braid that bridges the uj on the steering column

[au-yt]

Hidden fuses I haven't considered ,earth i will check, there wasn't a earth accross the the uni on the steering. But there was an earth to the grease nipple on top of the rack.
I have identified the horn relay.
Away from home at present. Lots of things to check
Many thanks for the insight.
Graeme

[alan]

you need the earth braid on the uni if it is the original one with rubber bushes

[au-yt]

Interesting there wasnt any remnants of a briaded lead when I took the uni appart.

[JJDraper]

I think this has been posted here before, but here goes..

Jeremy

[au-yt]

I managed to work this out. and at the same time the car had been fitted with an alternate horn switch.
The Air horn Pump isn't putting out enough pressure so all I get is this odd phuvvvvvvvvv noise.....
I have had the pump out and all seemed OK and swapped the polarity with no luck. gee I hate doing jobs twice
Graeme

[oldchieft]

Vanes in the pump are likely sticking.

Take the the cover off, take the vanes out and clean with wet and dry.

Dont lube with oil use WD40, oil makes the vanes too sticky to follow the the contour of the casing.

Just a squirt of WD40 in the inlet now and then keeps things nice.

Jon the Chief

[Quart Meg Miles]

My Maserati compressor seized its bottom bearing in 2008 after three decades but it's been fine since I cleaned it up. Have never had trouble with the vanes using 3-in-one oil but I don't use the horn much; in fact I had to replace the trumpets, one of which went solid, with a cheap kit and gave the new compressor to an MGB.

[stugilmour]

Had an issue with my replacement FIAMM air horns. The sealing of the tubing from the compressor to the horns needed extra clamping to seal well enough. I thought it was an electrical fault for the longest time.

Stu

[au-yt]

I posted this in the Recommissioning 71 sprint but though it worth adding to this.

The Airhorns are now fully sorted.
When I rebuilt the steering I connected all the earths that were either non existent or had poor conductivity.
I found the relays and cleaned the connectors. A little interesting snippet I just found and I bet others have as well, as I was just getting Fuvvvvv out of the horns.
Thinking there was a stuck vane in the pump, I checked that and motor runs very well. Assembled and putting a finger over the end of the pump out let......Fuvvvvvvvvvvvv. obviously even then there isn't much pressure.
I had checked the horns with shop air and they worked. As an experiment I wound the trumpet out of the housing half turn.... Bingo noise. I am yet to adjust the length of the horns to judge the effect but I guess that how they are adjusted for different sounds.

Cheers
Graeme

[Quart Meg Miles]

.... As an experiment I wound the trumpet out of the housing half turn.... Bingo noise. I am yet to adjust the length of the horns to judge the effect but I guess that how they are adjusted for different sounds.
Graeme

The pitch doesn't change but as your horns worked on a different air supply the gap between diaphragm and horn start is critical on air pressure. Years ago I fitted some ear plugs and fiddled with the gap and it had a peak volume position but that was all. As I recall the horns were perfectly set up as bought.