Troubleshooting is a common practice these days on anything with wheels unless the problem is staring you in the face like an oil or coolant leak. When it comes to electrical issues however the game changes. Basically when an electrical system acts up most times it’s a needle in the haystack scenario. Luckily Freightliner kindly developed Diagnostic Link 8 software that hooks up to the diagnostics on our Thomas buses so there’s a fighting chance of figuring out what has gone wrong.
I posted this video because of the easy steps to troubleshooting the no horn problem. The template for the horn comes up and it’s just a point and click test that determines where we have to go to seek out the fault. In the video you saw how the circuit flows from the horn button to the bulk head module then on to the horns. According to this analysis the problem is either the wiring to the horns or the horns have failed completely.
So the time saved not having to disassemble the horn button or check circuits in and out of the bulkhead module is worth the price of the software considering how much time it takes to dig up wiring schematics and trace harnesses all over the place. Once you use this software a few times and get comfortable with it I guarantee you will not want to go without it.
Since checking out this problem we found issues with the horns themselves. Now it’s very true that we could have gone directly to the horn and tested for battery feed and ground but if there is a problem somewhere else the software will come in very handy. The other accessories like wiper motors, heater motors, washer pump etc. can be checked out the same way. It’s all about the inputs and the outputs from the beginning to the end.
I can tell you from experience that using a software that can look at the multiplexing system on a Freightliner or anything other brand is a valuable tool that saves time and money. The Bulkhead module is the center point for all of the inputs and outputs controlling the body side of the bus. The headlight switch goes on and that signal is transmitted to the bulkhead module which relays that signal to the headlight to either the high beam or low beam circuit. Diagnostic Link software sure beats manually fishing through hundreds of wires.