Electrical Problem Solving – Thomas C2 School Bus Windshield Wipers
Tracing out electrical wiring by hand is a hardship and time consuming. Thanks to original equipment manufacturers there are very good resources out there to help out. In this case for our Thomas C2 school bus the accessfreightliner website is easily accessible for electrical schematics.
The song playing in the background was “Cat Scratch Fever” by Ted Nugent…go Ted!
Once you log on with a user name and password the next step is to enter the vehicle identification number. From there go to “PartsPro” which is on the home page. There is a FCC (Freightliner Chassis Corporation) link where a list of sub groups will appear. Everything from electrical components like the bulkhead module, power distribution module and our wiper motor assembly are available to search through and find parts which leads to the wiring schematic.
Once the part is located you can highlight the part number by clicking on it with the mouse and then clicking on the “EZ Wiring” link in the tool bar. This will bring up the wiring schematic and how I found the schematic you see here. It shows exactly where the control signals come from and how the 2 relays work to run the high and low speed of the wiper motor.
As you can see above this is the schematic for the electrical wiring for the windshield wiper circuit. The complaint was no low speed so finding the appropriate wiring diagram was essential to have a fighting chance on solving the problem. electrical problems are difficult and time consuming especially if you start going down the wrong path.
The C2 school bus is much like the M2 highway trucks by Freightliner and just have a school bus body on them. The Bulkhead module is the brains behind the multiplex wiring so looking at the schematic you can see as I mentioned in a previous paragraph that the BHM sends the signals to operate the wiper motor relays.
The video shows the location of the relays and fuses. It’s almost hidden up and under the cab and firewall but once we dragged it out of there the obvious problem was a resettable fuse had failed. It was definitely the factory fuse so it lasted eight years…..not bad.
This was an easy fix but just think if there was nothing available to refer to with the electrical side of the wiper motor? It would be like a shot in the dark trying to fumble through the wiring tracing circuits. Getting the proper information is priceless and worth the short time it takes to log on and do a quick search on the factory site which will cut your diagnostic time drastically.