fir st of all,welcome to CAC!!!!we hope ypo'll enjoy the forums,
2nd,the horn.....

,are in the fornt corners of the body,above the marker lites and off to the side from the headlites(If you open the headlite doors and try to peek into the front quarter panel you MIGHT see them),there are 2 green wires that feed the left side plug (drivers) and one for the right,they are grounded by the ground wires that go thru the bolts.
loose front spoiler...(bottom valance????) are just some small 1/4" or so bolts thru the bottom(crawl down there and take a peek,you'll see them.
as for the gas gauge someone else will chime in to steer you as to what to look for!!!