Experts - good 12V source
 

I am adding 118db horns to my early 911. Does anyone have a reccomendation for a good 12V source for the horns-via-relay? I am looking for something that would be clean and somewhat factory looking. Any advice would be appreciated.

Install another relay in the fuse panel (they are the round ones in red or black.)
Use the ground from the horn button to switch the relay. It should be obvious which one is the ground from the wiring diagram.

Tap into one of the large red wires at the fuse panel. For the 12V source. Run a reasonably large wire to the horn itself. Ground should come near the horn, if I remember correctly.

Doug

are you planning to wake up the dead.... :eek:

No waking the dead - just tired of not being seen.

Doug - thanks for the reply. Are you saying not to use the relay that came with the horn(kit)? Also, don't you need current to trip the relay?

I does appear to me that the factory horn had both a + and a - going to it.

The factory horns are already on a relay. You can hear it click with the horns disconnected. Why not just continue to use the OEM relay already in the horn circuit?

Well, to be honest I had wondered about that, but others have said I would be pulling too many amps through the horn button on the steering wheel. So the horn really does have it's own relay (in 1972)?

Still using two batteries??? An unused accessory screw for a power lug is available on the right side battery positive terminal, and the relay could be mounted close by.

Afraid not - down to one battery.

But I do plan to add the other one day.

Warren - I know you have extensive knowledge about the early cars. What is your opinion about adding another relay?

I really don't know if there was a relay in 1972 (there was from '74, on). Disconnect the horns and do the "click" test. If there is a relay there, you'll hear it. In any case, you DO want a relay on the horn circuit.

If the early cars have a relay, then just use that. In that event, only trigger current runs through the horn itself.

I am aware that many add relays to run the lights - any chance you are confusing that with the horn?

My '71 had a '86 wiring harness added, so I don't really know the early car, as well.
Doug

David,

There is a horn relay in all early cars -- rated at about 20 Amps. The nice thing is ... there is factory wiring to both front fenders already in place, taped-up where not used. You could place air horns at both corners -- if you wish! The factory horn wire is Black/Yellow at both 6-pole bulkhead connectors and to the battery box area. There is a two-wire pigtail with both Brown ground wire and the Black/Yellow hot wire for horn.

Thanks Warren - one more question - were the two factory horns on opposite sides of the car or just on the left. When I got my mostly original 72 it only had the high note horn on the left with no dangling connections for the other horn. I have never checked the right side as I always thoght they were both on the left.

The two factory horns were always mounted together and on the left side per early factory wiring diagrams, but it could be on either side after all these years, now, with all the 'imaginative' POs out there.

Warren - were there two sets of leads from the wiring harness to the two horns, or did they "daisy chain" off one another? I can only find the one two pin connector to the high note horn.

David,

They were daisy-chained.

When you get it hooked up can you vid it for us like these guys did??

http://www.youtube.com/watch?v=iP2MgvEsBVY

OMG - I am dying - or ROTFLMAO. I certainly HOPE that's not what I got - there just the round, red Hella horns for sale in auto catalogs. My little high-note-only hron was getting a little embarassing - and at times my car seems invisible to others.

Warren - do you have an opinion on adding an additional relay or just using the relay that came with thte car? These are no air horns!

David,
A 20amp relay is more than sufficienct. That's a lot of juice.

Doug