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Hi all, I was wondering if anyone could offer some advice on the above-mentioned air horn set up. It's a bit confusing at present? Both of the compressor terminals are common to its earth body... The relay that's supplied has continuity between two terminals which energise the relay when putting 12v across also?

Someone somewhere, may have an original wiring diagram for these 1960's set up maybe?
Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net

Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net


Your help will be appreciated. Gary.
 
Both of the compressor terminals are common to its earth body...

How are you measuring the continuity?

What's the resistance between the terminals?

The relay that's supplied has continuity between two terminals which energise the relay when putting 12v across also?

They will have , it's a coil of wire.

Same as above;
How are you measuring the continuity?

What's the resistance between the terminals?

If they're 1960's multitone they're probably non compliant nowadays.
 
Yes normally with a gate or between two terminals that aren't common? This normally makes another terminal
Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net
live when the coil is energised, this one doesn't??

I have not checked the Ohmic resistance between the terminals, it's ringing through a continuity tester..

This is not going to be my main horn, just a bit of fun at shows through a separate switch.

Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net

Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net


Both of these contacts are common to the earth too??

Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net

Cables supplied with the horn are still attached...The black cable on the right goes to the bottom right terminal, that terminal is common the one that is stamped PUL, which is linked via the small brown linkage to the BATT terminal??

Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net


I managed to get this off the internet but I do not think this is right??

Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net


I did manage to find this on-line but unfortunately, the original document (you can see on picture no.5 top to bottom) you cannot enlarge but you can kind of make out what it is...

Vintage Maserati/Harry Moss Air Horn SOLD (1960) on Car And Classic UK [C462960] - http://www.carandclassic.co.uk/car/C462960

Anyways, someone might say this is easy, I have it running and clicking through the relay but I don't like the splashing, it's almost as if there's a dead short..

The compressor weirdly will run either way by putting 12v across the terminals, it makes no difference across the terminals which way around this is, meaning whether the comp is sucking or blowing, it blows both ways!!

My other thought is negative earth switching??

Thanks to all again and hopefully some of the above will help..

Gary
 
Last edited:
Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net

please make sure you fit a fuse as the compressor is high load and will melt the loom if it siezes (fire warning)


EDIT LOOKS LIKE YOURS IS COMPLETLY DIFFERENT
 
Your horn is wired for positive earth as it is .Remove the link wire between pulse and bat then conect the relay to earth as shown on your coloured diagram. Then you need to conect the pulse terminal tp the positive side of the horn.
please fuse the battery conection


Maserati Harry Moss air horn set up? {filename} | ElectriciansForums.net
 
Last edited by a moderator:
Thanks My key for taking the time to do this and aid with some advice, I'll give that a go.

I would always fuse any item or load.

My only concern is the metallic element of the compressor being all metal with both contacts being common to earth. This surely can't be right as you are putting 12v on one of those contacts and with it bolted to the main steel structure of the car, that's a dead short is it not?

I will also see if the bracket is common with that tag on the relay which I think is earth..

Thanks Gary
 
Hi,the two connections on the compressor,are,or should be,separate. One goes to the chassis earth,the other to the relay switched live.

I would check the amps draw on the compressor,and select a new relay accordingly.

Nice to see a bit of the earliest automotive add-ons...even if it does look like a trawler winch ;)
 
My only concern is the metallic element of the compressor being all metal with both contacts being common to earth. This surely can't be right as you are putting 12v on one of those contacts and with it bolted to the main steel structure of the car, that's a dead short is it not?

If both contacts are Zero ohms to earth,(tested with a multimeter not continuity tester) then the compressor windings are burnt out and it's useless.
However you say it works so it's most unlikely it's zero for both terminals.

If you don't have a multimeter,
Connect battery + to the casing and battery - to one terminal.(don't use the relay)
If it spins the unused terminal is connected to the compressor body.
If it doesn't spin connect to the other terminal.
 
Right guys, this is all working pretty much how I wired it before but it does need the ink between the two terminals or like My key said, the second cable from the horn which for test purposes is the shunt loop.

I think rather than trying to run the two independently, It would be good, through a rocker or an additional relay or with a new relay with the additional terminal, to switch between the two via a rocker switch.

One supply powers the air horn, the other side or gate of the relay drops and when flicking the rocker the other way, that side drops and the original horn will sound.

Any of you fancy a challenge with that wiring diagram, brill chaps....!!

Thank you all for your help above, brilliant.

I'll be putting a video on here of the horns working shortly but not tonight, the neighbours will kill me as just gone 12.30 in the morning and I don't mean midday!!! ATB G
 

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