Train Horn Writeup Part 2 of 2: Installation

Posted on: June 20th, 2011 by Child of the Sunfish

This is part 2 of the train horn writeup. Part 1 can be found here.

Once I had all the bits, it was time to install them. Firstly, a clean workspace needed to be made.

Next, the compressor.

The compressor required some thought because it had 4 screws welded to the bottom of it, so bolting it straight to the chassis was not a possibility as it was not possible to get to the otherside of the chassis and tighten the nuts. I got 2 x 250mm lengths of gal dipped unistrut from work (shown below) and drilled 4 holes for each screw, which allowed me to bolt the compressor to the unistrut. This meant though that when the compressor was in use it would vibrate and make quite the racket against the steel unistrut. The solution was to obtain some rubber strips with a sticky side to put between the compressor and the unistrut.

The unistrut was then bolted down to the chassis of the car, as per below. The air tank was able to be bolted directly to the car as it had mounting holes, and this was installed on the other side of the sub. The rubber hosing shown in the pic will be fastened somehow, but I’ll worry about this later on.

Lastly, the mounting of the two bells. I had two L shaped brackets, which I was able to fasten directly to the chassis. I used my impact driver to tighten the screws which made for an incredibly tight fastening. There’s no way these brackets will be falling out. You can see the two brackets in the picture below. The bells have to be turned sightly down to prevent the accumulating of water inside them.

You can see both horns mounted in the picture above. The last step was to connect the air lines, which was done using a T-piece that I got from my uncle. This fed both horns.

Now everything is ready wire up.


Two sets of cables were run, one for the compressor and the other for the horn solenoid (the coil that activates the horn). The compressor was fed from the accessories wiring loom, and the cables for the horn were run directly from the battery through a 5a fuse and the pushbutton inside the car.

The battery wiring for the horn, and the wiring loom feeding the bells.

The switch was installed just below the steering wheel for discreteness and to keep the factory horn in original condition.

The last step was to wire up the compressor, which required the use of a relay. The reason for this was because there is an override switch and a pressure switch on the compressor, and if the feed was run through both of these things, they will be subjected to the F.L.C (full load current) of the compressor. Switches etc… are usually rated to withstand 10a, and the max demand of the compressor is 25a, which can potentially mean meltdown. A relay allows you to connect all of your sensors to a coil, which will connect the feed to the appliance once power is applied to the coil, which creates a magnetic field that clamps the connectors inside shut, so the F.L.C bypasses your sensors. Instead of running a new cable from under the dash, where the accessories circuit originates, I tapped into an existing cable that I had previously run to the amp, which let the amp know when the ignition was turned on so it could start up. Obviously I powered the relay using the ignition cable, as I don’t want the compressor going off whilst the car is off.

Above you can see where the active has been taken from, and the relay used for the control wiring. Finally, to neaten up the cables, as there were a few, it was all run in loom, ready to be secured in discretely.

And that’s how I installed my new train horn. It’s got a few comments so far, mainly because of the output. I rolled up at my parents house and my mum came to the door and jumped for like 5 seconds, then my sister came out and said she was drinking at the time and she spilled water all over her face. All in all, it was a fun project.