My horn's always sounded puny. I don't think the low one works. I have a set of quad horns form my Dad's 87 Buick Park Ave, they sound awesome-like a classy freight train.

Anyway, I will mount them a pair each side of the radiator. The wires that powered the original F150 horns splits off from the loom going to the fog light on the right. There are an identical pair of wires on the left side, but they don't power up when the horn is energized. I'm wondering if there was an option for extra horns, and if I could add a relay or something to power up these wires? I could add a relay and wires but I prefer to use factory wiring if possible.

Thanks.

 

The connector on the driver's side could be a few things, but it is not for horns.

1. Fog lamp connector ( if you don't already have them ).
2. DRL resistor connector, if you do not have DRLs.

The horns, if they ran on the Buick I think the horn relay on the F-150 should be able to drive them without an issue.
You can try jumpering them from the Ford connector, to see if they will work ( if they are having a power issue, they will sound anemic / wimpy ).

If you need to, a relay would do the trick, but with larger wire.

I added another F-150 horn set to the driver's side on my '06.
I wired both sets together with 14 AWG wire to a relay and powered it from the fuse panel I added under the hood with 14 AWG wire.
2 reasons for this, 1) my load was 2x the factory load 2) to make sure the horns were not going to have a power issue on the smaller factory wiring.
I did not have a dB meter to see if a single horn benefited from the larger gauge wire, but I had the AMP draw issue as well.

 

I do have the fog lights. The wire I'm wondering about splits from the harness that goes down to the fog light, just like on the right side where it comes out to power the horns. I do not have DRL's, so maybe that's it?

I wouldn't be comfortable adding double the load on the factory wiring without a relay.