Does a 1986 freightliner flc120 have a jake brake it has a 425 cat in it 13speed

It was available as an option.

 

Maybe maybe not. It may have a switch and not the rest or have the rest and not the switch. Lots a things can change since ‘86.

Like @Dale thompson said they were available as factory option or add on. Certainly still common to get one without it though

 

Jake switches are the ones above the tractor/trailer knobs. If they’re not there, remove top panel and look down for the wires. Should be 2 groups of wires with 6 prong connector plugs. If you find em, you can run a jumper wire to see if they work.

 

That's sharp!

 

How about some details on the making of that dash panel?

 

I would think that most people who would spec a four and a quarter cat would go with the engine brake option BUT each build is different but the above poster pointed you in the right direction, look behind the panel.

Remember that corporate trucks are ordered after a bunch of negotiation between carrier and builder.

Often the corporate bean counters get their input and limit the actual end result. Just because you find the connections; the opposite end may not be connected and almost 40 years out of the factory can compound what is there or not and if it works or not.

 

Another hard truth is I can’t tell you how many trucks of all makes I have come across that by build sheet left the factory at 425 with x options. Only to have a motor swap done for one reason or another and end up with an economy 285 or 310 with no Jake. Course everyone thinks they are the same or it’s a Money thing. A lot of stink can be changed in 40 years