I'm looking for a connection point for my Federal Signal SW300. I need a direct battery connection but it can only be hot with the key.

 

You will get other answers I'm sure, but I am a firm believer in NEVER overloading a circuit. That means go direct to the battery with a cable large enough to supply the MAX load that that control box will EVER have flowing through it at any one time. I always do amp clamp test so that I KNOW without a doubt what that # is and then cable and inline breaker AT the battery at least 125% of the max load. Depending on what that # is, I would use a heavy duty relay (you can get them that are about twice the size of a regular relay and may go to 50 amps or more) and control that with a low amperage "ignition on" source to trigger the relay. If the load is really high, say 60 amps or above, you could use a heavy duty constant duty solenoid, triggered by a low amperage "ignition on" source, but you need to make sure the source is able to safely handle the draw of the CDS, which MAY be higher than the relay.
Just remember, electricity runs on smoke, and if you let the smoke out of the wires, the electricity doesn't work any more, and you don't want that!

 

That means always on.That's called "switched". So you're contradicting yourself. What do you mean by "direct battery connection"? A heavy wire to carry a lot of current? Then that's what you need. If you want it to be off with the key, run it to a heavy relay, and trigger the relay off a key-switched circuit (like the EEC PWR relay). These captions describe how to add a circuit safely:

 

i used to wire emergency vehicles - you can take this for what it's worth.......

the switch box you have is not made to handle loads.... it IS intended to control heavy duty relays that control the loads.

the smaller red and black should be tied into the dash lights to control back lighting of the legands abouve the switchs

the larger red should be fused at 10 amps and tied into the acc. curcuit like the radio or something

the switch outputs going to H.D. relays

fuse each relay from the battery rated to the load

 

its fine the way its wired now. i'll just kill my battery everytime i forget to turn my lights off running in to the fd.

 

i have my big aux grill lights connected to the 40 amp relay circuit and the rest connected to my strobes. they don't draw much power.