Freightliner OPT Switch Guide: What Does OPT Mean In a Truck?

You will get many explanations. The problem with acronyms and abbreviations is that so many meanings are attached to the same few letters. That can leave some owners confused and trying to come up with some sophisticated answer to why there are OPT switches on your dashboard.

The letters OPT normally stand for the term ‘optional’ and when you see these switches on your dash, you are at liberty to use them wisely and at will. There is nothing special about them although they may light up when you push them to the ‘on’ position.

To learn more about this trucker or RV shorthand, just continue to read our article. It has the information you want to know about so you can understand what the different switches do. Take a few minutes to get this information and ease any confusion you may feel.

What Does OPT Mean in a Truck?


They say that if you put 4 archaeologists in a room, you get 7 different opinions. That is going to be the case for these three letters when it comes to RVs and trucks.

One owner stated that Dynamax uses those switches for an AUX battery connection and the other is unused if there are two of these in your RV. If you ask a person in the transportation business you will get a completely different answer.

OPT to them stands for ‘over the road package transport’ and has nothing to do with switches. On an F-150 discussion forum, only one person got the definition correct while the rest of the responders to the question said it had to do with the tires on the F-150 or light trucks.

However, the correct answer is those 3 letters when it deals with switches, which means ‘optional’. In other words, you have some free switches you can connect to just about any feature you want to and use the switch to turn those features on or off.

These switches usually only have the two positions so you won’t be able to connect any fancy features that require dimmers, etc. You will be only able to hook up those features that only require a simple on or off switch.

What Does The OPT Switch on Freightliner?


If you go to a truckers discussion forum, you will get some pretty funny responses for what those letters mean. Some examples include- ‘oh, please take me now’ when you scrape the underneath side of the overpass with the top of your trailer.

override police tickets’- when you push it, the officer disappears. And finally, ‘it is the ejection seat button that sends you through the roof of your truck, and don’t press it when you are in a tunnel.’

Those are humorous responses to a simple definition that means ‘optional’ When you see the OPT above some switches, those letters are referring to ‘dummy switches’ which do not do anything until you hook them up to something.

There is nothing special about these buttons unless you have some extra lights or horns, or other accessories you want to hook up to make your RV or truck look or sound cool. In other words, the manufacturer is giving you some switch options if you need them.

Turning them on or off will not impact the operation of your truck or RV when they are not hooked to anything. You are left to your imagination in how to put them to good use once you get familiar with your RV or truck.

People like to customize and manufacturers are aware of that desire so they went ahead and provided switches so you do not have to ruin your dash to add more.

Freightliner OPT Switch Wiring Diagram

The following is the best wiring diagram we could find.


You can try to match this diagram up with the dashboard diagram that follows:


Notice the two OPT switches at the top to the middle right of the diagram. You may find that any wires that are connected to the switches dead end somewhere on the chassis or some other harmless spot.

You may not find a specific wire diagram for these switches because they are part of the whole dashboard assembly. You will be looking for a wiring diagram that covers all the switches on that assembly to find the wire that connects to these switches.

It seems there may be one to the fuse box and there seems to be a dedicated fuse for these switches. So if you pull the assembly off, you can trace the wire to that fuse.

It will all depend on the manufacturer and how they decided to wire these switches. These may have independent functions when wired but they will not be independent from a wiring diagram and come with their own.

Freightliner OPT Switch no Power


There is no real power to these switches. Some owners have reported that they will illuminate when you press them to the ‘on’ position. The power to them will be minimal and will only power the light.

Others may not have that feature but that would depend on how the manufacturer. Without hooking them up to a feature or accessory, there should be no power to these switches outside of that one function.

If you do hook them up to a feature, as you will see in the next section, there is a fuse connected to them. If the feature does not work after wiring everything together, check the fuse box.

One thing you should know is that these switches are not ignition controlled. That means that they are always ‘hot’ and will drain the battery of power when you switch them on without the engine running.

Also, the main wire for this switch may not go to the very back of your unit. It may terminate somewhere between the firewall and about 8 feet ahead of the tow accessory wires at the hitch.

Freightliner OPT Switch Fuse Location


There is a lot of good news in this section. The fuse is located in the fuse accessory block on top of the driver-side wheel well. Plus, it is a 20-amp fuse. But the story does not end there.

We cannot replicate the pictures for you as we do not want to violate any copyright, etc., rules however, one driver has taken the time to trace the wire from the switches to their termination points.

He has photographed his journey showing you the fuse, the fuse box as well as the most important wire if you want to use those switches. His photographs will be better than the wiring diagram placed above and any wiring diagram you can find on the internet.

You can find the images at this link and they start at post #15. A second set of images start at post #17 and continues through to post #19. Don’t ignore the typed content as it is very informative.

The poster murraym has a lot of information in previous posts before you get to the images so take some time to read them. They will help answer many of your questions.

Once you find the termination points, then you can decide how you want to wire your accessories.

OPT Switch Options


There are many different accessories you can wire to these OPT switches. The sky is the limit as long as you stay within power restrictions and fuse strength. Here are some accessories or needed pieces of equipment you can wire to those switches:

1. Flood lights- help light up the rear of your trailer or RV. This can be called trailer spot lights as well.

2. Dock lights- like flood lights, these will add some extra lighting to your RV or truck and make it easier to see what you are doing These lights and the flood lights can be used to help you keep your eye on your cargo if you are pulling a flat bed trailer.

3. Trailer air dump- good for your air brake system.

4. LED mood lighting- if you want to spruce up your interior look, these are the switches you can use to turn those lights on and off. They will work for exterior lights when you want to add some color to your truck’s or RV’s overall look.

These are just some suggestions you can think about. Talk to some experts on these switches to see what other options you may have available.

Some Additional Words

Having options is always important when you are on the road. With options, you can do so much more and even provide another level of security to your RV, etc.

Those option switches are just dummy switches that do nothing until you hook up some accessory or mandatory part. They provide you with options so you can make sure your vehicle is fully equipped with everything you need.

It is great to have these types of options when you like to customize your vehicle and make it more versatile.

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