Does it matter if the temperature sender is installed on the port or starboard head? I have a horn that is installed on the starboard side but I am not sure if it works. I would rather a temp gauge. How do I check if the horn is working? everyone says ground it out. How specifically do I do that?

Thanks

You are better off with a water pressure gauge.
Put a temperature switch on each head so if either side gets hot you get an alarm.
To check it, follow the wire coming from the switch, it usually is connected right by the switch boxes.
Turn on the ignition switch, jump the connection to ground and the horn should sound.