Horn Relay?

i am going to put an alarm/remote startin in a infinity g20. now the customer already has an airhorn replacing the factory horn. there is a relay under the hood already powering the air horn. now when i wire in the horn ouput of the alrm do i need to add a relay even though there is one undser the hood alraedy. can i just go right out aff the alarm to the horn wire.

if i need a relay can i just hook the horn output to the relay under the hood

please let me know

thanks

there is a new installed realy under the hood for the air horn. so should i install another realy off the alarm or just run the horn output straite to the horn wire in the car

thanks