Freightliner Truck Wiring Diagrams

[Laurene Arrison]

Wheneverpossible, we make sure to color code the wiring diagrams to match the actual colors of the wire on the vehicle itself, which often exceeds what the OEM wiring diagrams look like. This is an example of a Freightliner Cascadia trailer receptacle wiring.

Freightliner wiring diagrams can be hard to find, but we have them inside Diesel Repair. You can book a demo or create your account and get started immediately. The Diesel Repair platform also has other valuable information for Freightliner Trucks, such as diagnostic fault code (DTC) repair information, recalls, technical service bulletins (TSBs), component locators, labor time guides, remove & replace instructions, and much more.

I have a 2008 Freightliner chassis (Tiffin Pheaton, 40 ft). My Parking Brake Light comes on intermittently while driving down the road. The air pressure is good (brakes do not engage). I have had this problem for about a year. The problem is more constant now, then intermittent and I need to fix it. I have replace the Low Pressure Switch located beneath the Park Brake Release Knob. I have even bypassed the Low Pressure Switch by replacing it with an On/Off switch. The problem continues. I heard there is another type of switch located somewhere else. Can someone tell me where it might be. I have called Gaffney and they told me it was probably something Tiffion hooked to it. I called Tiffin and they said they have nothing connected to that system. Please help. In addition to the brake warning light and buzzer, my driving lights turn off and on in unison with the brake warning light and buzzer. A new development is that my electric slide outs (2) seem to be acting up in that I sometimes have to move the ignition switch on and off a couple times to get them to work. Thanks. ( I have seen several forums related to this problem but have never heard from anyone who had actually corrected it.

The alarm sounds while driving. Sometimes it starts immediately after putting the transmission in Drive (after releasing the brake). Most of the time it is activated / deactivated by bumps in the road. Any idea where that common ground would be?

Like Wayne mentioned one needs to look around and check connections. You might be able to get some wiring PDF files for your chassis from Freightliner. You will need the VIN number. Also check with Fleetwood, you will need the FIN number for the coach. there is a plate with that information is often outside on the drives side below the window.

We are currently sitting at a RV Park in Albuquerque. Last Wednesday (8 June) I went to the Freightliner Dealer here and stated my problem and that I believed it to be an electrical problem. He said that I could come to the shop on Friday (10 June) at 6:30 AM and they would PROBABLY be able to take a look at it mid-morning (they operate on a first-come-first-served system). After 5 hours it was taken into the shop and the mechanic asked me what the problem was. He said that the Brake Light was not on when he drove it into the shop. I started the RV, Pushed in the Brake Air Release and put it in Drive. The buzzer and light started immediately. I told him that I had changed the Low Pressure Switch with no change to the problem and that I thought it was an electrical problem, maybe a short or relay or something. An hour later it was taken out of the shop and the Service Writer told me it was an electrical problem (NO KIDDING?). He said they may be able to get it into the shop on the following Tuesday ( 14 June) depending on how long it takes to fix the vehicles ahead of me. I honestly do not have much faith in their ability to find the problem and I can't imagine the cost. I would hate to spend $1000 and have the issue arise again when I am 50 miles away. I specifically chose a Freightliner Dealership because I wanted; it done right. I am just not comfortable with the way things are going. Anyway, since I am stuck here for a week, I decided I might try finding the problem myself.

I appreciate the helpful hints. Cooling level sounds a bit off the wall, as you said, but what the heck. I will check it out. I will also call Gaffney and also try to get wiring diagrams. I researched purchasing the repair manuals, but I was told by the parts guy (in Austin, TX) that they did not include wiring diagrams. Do you know if this is true? Do they include wiring diagrams?

I spent several hours looking at the wiring diagrams in the owners manual and checking things. I discovered that there is a Green Wire running from the front panel (under drivers window) to the rear panel (last bay on passenger side) that connects to a solenoid. It was barely holding on and came off when I pulled on it. I reattached it and tested the slides. They worked fine. I then closed the coach up and took it for test drive. NO BRAKE LIGHT, NO BEEPING!!!! It appears that both issues were the result of that one loose wire. We will be heading to the Grand Canyon in the morning. Thanks for the help. Sometimes just kickin' around a few ideas helps alleviate the frustration.

Herman's explanation above isn't too far from what I was thinking. Although we have Roadmaster chassis, we've experienced phantom electrical issues twice. Both were tied to failed coolant level sensor. Once sensor was replaced the issues went away. Weird thing is, is that my diagnostics reader did not show a code. Last time it happened it took a wiz mobile mechanic with a fancy computer to get the code. Part was cheap. Price of the expert mechanic was well worth it.

It'll just die. Might be hitting some washboards. Cycle the key and it starts right back up. Normally. Today it died in the bean line at ADM. Didn't think it was going to restart. ECM has been replaced. Fuel shutoff solenoid has been replaced. It has done this ever since I've had the truck. Might not do it again for 20k. The ECM is wired hot to the batteries. I just don't get it. Even thinking about changing the key switch. Generally, when it dies, the check engine light comes on and it cuts out. Today when I turned on the wipers the check engine buzzer came on for just a second but no lights. I The circuit breaker panel looks O.K. Grounds look O.K. About ready to start pulling panels out of the dash and see what's back there. Anybody had similar issues?

Why would you need a new key switch, if engine's ECM is truly completely "hot-wired"? meaning ALL ECM ground wires, ALL constant 12 VDC ECM wires and the keyswitch 12 VDC "ignition" wire(with external toggle switch) should have been "hot-wired" to ECM, to eliminate anything to do with the OEM cab's electrical wiring Maybe your idea of "hot wire" isn't the same as ours.

The thing still turns on with the key, so I'm assuming a voltage problem somewhere. Occasionally, when I've say, turned the fan on high, it will kill it. When I started the wipers yesterday the engine warning buzzer went off for a second.

Heck, even looking at that little schematic, and you mentioned the 3 pin connector is going directly to batteries, that still leaves "possible poor connections" from 3 pin plastic connector over to 28 pin connector and/or corrosion in 28 pin connector, besides all the "cab electrical connections" that feeds the keyswitch, then returns back to that 28 pin connection.

When it comes to dealer level diagnostics, accept no substitutes. This TEXA diagnostic laptop kit will do what you want it to do: Dealer level functionality on virtually anything you run across. From reading and troubleshooting codes to performing forced regenerations and injector cut-out tests, the TEXA is the tool for the job.

3a8082e126