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The locking switch does not come with any type of gasket for installation, so I had to improvise. I used two plastic rings from a spool of 50 blank CDRs. With a bit of Dremel work they fit like a charm. (Before and after pictured below)
With the lock mounting out of the way I got back to the actual wiring worries. I noticed that the horn relay under the hood runs to a 20A circuit, while the interior light door switches run through a 10A fuse behind the glove box. Originally I had planned to splice the horns into the interior light circuit, but apparently that was not going to be a wise choice. I decided to pull the bottom cover off of the steering column to see if I could splice into the horn circuit closer to the horn switch. After a bit of investigation, I found the wire running from the horn to the relay. It is a single red wire with a yellow stripe, attached to a large plug just behind the steering wheel.
At this point I realized that the horn switch just grounds a hot wire to the horn relay under the hood, which actually controls the horns. This works out quite well, since the relay circuit seems to run a fairly small current (~.5A). I decided I would eliminate the interior light positive (solid yellow) that runs to the door switch plug, and run the horn to the plug instead.
On both the driver and the passenger side I cut the electrical tape back about 3" from the plug, then cut the solid yellow wire. I crimped a cap on the live side of the wire, leaving 3" of solid yellow wire on the plug side for me to splice in the horn jumper. I decided to insert the locking switch on the jumper between the horn relay and the door switch plug.
Since I wanted both doors wired into the horn, I had to run a wire across from the passenger side to the driver's side. I followed the existing wire loom across, zip-tying as I went.
The wire to the right side was spiced into the passenger side plug, then shrink wrapped and finally wrapped in electrical tape. The crimped cap on the old interior light wire is visible in the right picture below.
The wire from the passenger side was connected to the driver's side switch, both of which were connected to one side of the locking switch. The other side of the locking switch was connected to the jumper from the horn relay on the steering column. Connections were crimped, shrink-wrapped and tapped up, and everything was re-assembled.
This is a final view of the lock from the outside.
I also purchased a small red 12v LED to attach to the dash, but I am holding off on installing until I can find an appropriate blinking LED. The horn will be a nice wake-up call for me, and it will certainly get the attention of a would-be thief, but in some cases a nice visual warning (other than the lock) can make all of this unnecessary.
The overall time I spent on this project, once I had secured the parts, was about five hours. Most of that time was spent following wires and checking circuits. If I had to do this again, it would probably take less than an hour. The total cost of this project is less than $10, especially if you have a nice selection of wires and connectors sitting around. I do not think the lock detracts from the appearance of my Jeep, and I do not feel inconvenienced by the fact that my interior lights do not come on when I open the door. I can easily turn them on using the headlight knob. In my opinion it was a simple, clean, functional modification and I am very happy with it so far. I will definitely be sleeping easier, not feeling the need to jump up and look out the window at every sound.
If you have any questions, you are welcome to email me.