The Siren Board

Don't go to Radio Shack to buy a 120 volt relay. Shop with a company like Mouser or Digi-Key and order a relay with a continuous duty coil. If you want to run a 6 volt siren from a 12 volt battery, go online to a site like this:

http://www.mamotorworks.com/acvw-air-co ... -4969.html

which sells large resistors and voltage-control devices for operating original 6 volt accessories on pre-1966 Volkswagens with an upgraded 12 volt system. Or go to Ebay and buy a cheap 12 volt siren.

I'm still lost on this

Mac wrote:Do all relays work with the power being cut turning them on? or is that a specific type I need to find?

no. most require power to switch, and need that power to remain in order to stay switched. However, I see a fairly easy solution to what you want to do, since you can use the supply battery to keep the DC relay energized. You'll need a battery (duh,) a Ford starter relay, a 110 V relay that can switch about 5 amps, has normally closed contacts, is rated for continuous duty, and your siren.

I'll draw up a quick diagram in a minute or two.



This is one way to do it. how this works is that as long as power is supplied to the coil of the 110VAC relay, the contacts stay open. If power drops, then the 110VAC relay closes, which then puts battery voltage on the trigger terminal of the starter relay, closing the relay and operating the siren.

the problem you'll have is that you'll need to find an AC relay which can stay energized for long periods of time, and a way to keep the battery charged.

the starter relay looks like this:



and are cheap as chips anywhere; Ford used them from like the '50s up through the late '70s. I'm not 100% sure if they'll energize on 6 volts, or if they require 12 volts.