What would the amperage of a horn relay be?

What car/ application?
epending onwhat you're doing might be simpler to use a standard 5 pin that easy to find and available just about anywhere. Would prevent a "where'd this come from" for the next guy
AMZ LINKY

That's the point of asking. Those are rated 30 and 40 amps which I would imagine are sufficient.

FWIW, here is what I'm using ...

https://www.summitracing.com/parts/msd-7566-4

I don't know what the MSD relay boxes are rated for the relays shown can be had up to 60A and higher if one uses a 5/16 terminal. At the larger amperages doe be careful on the source. IE: Bosch, hella or other well known brand
What are you trying to control and what is the current draw?
Also is the current draw continuous or intermittent

A horn relay. I suppose it would be continuous if I get road rage !!

No need for 5 pins relay. 4 pins is enough. Stock is actually 3, since the power source and the positive trigger are the same on them (that would be the 30 and 85 prongs on aftermarket pieces). Horns relays are actually triggered by ground.

Dual stock horns use to be on 8-10 amps rate.

The coil windings inside the relay that activates it likely only draws 1/3 amp, maybe an amp at most but unlikely. The contacts that close when the relay activates is what handles the higher amperage for say a Fan, Horns, convertible top or other high amperage accessory.
So, if your just using it to activate the relay you should be fine
I'm a bit baffled as to why you would use the MSD relay pack to control the horn relay
hope his is helping

I'm not - I'm tidying things up and getting rid of the ugly horn relay. The relay packs control the fan, water pump. headlights, fuel pump, EFI and horn.

Are you asking the current draw of the relay itself?? milliamps

But if you are asking what the horns will be drawing through the relay, that depends on the horn(s) you have.

per the supplied part number, each relay in the MSD pack will handle 40 amps which "should" be adequate for the horns unless you have some big monsters on the vehicle.
The rest of the items you mentioned should be verified to be within the 40 amp spec. Myself if it's rated for 40, first question is that continuous or intermittent.
Obviously the horn would be intermittent.
Something like the fan should be considered continuous as would the A/C headlights etc.

Myself, if the relay is rated for 40A continuous I reduce that number by 20% or so for a "safety net". The cables/ wires should be sized depending on the distance from the power source.
If all four circuits draw 120+ amps continuous ( unlikely) you'll need a 4 ga or so cable if your within 5 or so feet of the power source. I would also encourage the use of fuse(s) as close to the power source as possible.

if something draws 40 amps continuous, what is the start up amp draw ?
i believe the relay should be rated for the highest possible draw the item will see.
also, please do not use the Hobo Fright 1,853 piece terminal kit [only $9.99] to wire up these high draw accessories. quality terminals, as well as quality crimping tools are a must.
just my opinion and life experience repairing wiring nightmares. your mileage will vary.

I think the only thing that would draw 40 amps or more continuous would be the starter motor

You guys have dragged this down a rathole. It was a simple question of how many amps the horn relay might be rated at - nothing more. I know how relays work, I know where to use them, and I know about ratings and wiring. All I was hoping for was that someone could tell me how many amps a horn might draw. And to clarify that, a '69 Road Runner horn.

Beg, buy or borrow a clamp on amp gauge and find out
Please let us know your findings, I don't own one or know anyone who does so I can't answer your question

I already replied to that. Never actually measured by any amp meter clamp, but what my ammeter shows on my car when clunking horns while engine is off. So it can not be a PRECISION measurement t but at least aprox.

That thought occurred to me and I think my DVM has the ability to measure amperage draw.

However ... when you look at the mechanicals of the horn "button" it sure isn't designed to have any significant current flowing through it so its no surprise that there is a relay in the circuit. My guess is the horn itself draws no more than ten amps whereas the relay may only require two or three. And then of course there's a "staple" to complete the ground circuit !!

You area asking two questions here.

Horn, who knows measure it but a stock horn relay is rated for 20A.

The relay, will not draws Amps, it will draw milliamps, as in 1000ths of an amp. 300-500 milliamps is typical for a light duty relay.

Not so, several aftermarket accessories can and do.

if your original question had been a bit more detailed we wouldn't be in the rat hole. Assuming what you were asking for and giving the wrong answer could be dangerous at best.
Sorry for trying to help.