RW 613 SuperLiner II Wiring

[phildirt]

I have no trailer brake lights from the foot pedal. Normal brake lights on the trailer with the maxi brake (yellow) button and the service brake (blue) button. Truck brake lights work normally from both foot pedal and both buttons. The issue shows up at both the trailer plug and the wiring terminal strip on the left hand side of the firewall (terminal # 14).

A jumper from terminal # 6 to terminal # 14 and everything is ok.

The wiring diagram shows a "trailer stop lamp sw" - feeding to terminal 14. Where is that switch located? Is it part of the service brake (blue) dash button?

 

 

 

[Vladislav]

So far I knew about the only brake light switch operated by air and it's located on the firewall behind the engine rear end (if straight 6). Two wires attached to it and the switch reacts either for foot valve, parking brake knob, low overall pressure or even the trolley valve. I'm not ready to tell is there any relay but what I have on my '88 R-model is the positive brake light wire comes to the firewall terminal to go further to the tractor chassis lights. And the trailer socket cable is just attached to the same terminals at the firewall connector to be in parallel to the tractor circuits. Sure all that could be a result of modifying but looks like was done at the factory.

[phildirt]

Thanks for the  response.

This apparently is set up differently.

There are two 14 post terminal strips on the left side of the firewall under the hood.

On the inner strip posts 4, 5, and 6 are stop, tail and turn signals for the truck - they all work on the truck.

On the same strip posts 7, 8, 9, 11, 12, 13, and 14 go to a 7 wire trailer cable that goes to a junction box on the back of the sleeper and then to the trailer plug.

#14 is for the trailer stop lights and it goes somewhere to get its voltage- it shows zero voltage from the foot valve, 12 volts from either the yellow or blue air valves.

There are no electrical connections coming out of the foot pedal treadle air valve.

 

 

 

[Vladislav]

The setup is similar to what you describe. Two 14 posts junction blocks at the left side of the firewall. Unfortunately I haven't had luck tracked the schematic for them. There is a full scheme for an R-model here in Viki section but it represents early models which differ from 80's years ones as I found out. I do suppose cab wiring on later R's and RW's is the same harness since see no reason making it different. And as I was told (by Matt Pfahl) that harness covers almost all factory options in its basic desing. So the harness must be the same. Ok, there were also 90's years harnesses with all the wires in white color with text markings on but multy-colored ones of 80's years must be the same.

What I had in my truck was trailer coupling cable attached to some 5 posts (stop, marker, back up, L and R turns) of the outer 14 posts terminal. And when I was looking for tractor stops I found them at one of those posts. Possibly it could be different but I see no reason to multiply signal sources, much easier to just parallel tractor and trailor. Some relays could be used though but I found neither of them at my truck.

Of brake light switches there's one unit attached to the outside of the firewall about its middle. It has two wires and an air line. It reacts on pressure change at some certain point in brake system and lights the lamps on. Again, I see no reason to multiply such switches as long as trailer lights must get on at the same time as tractor ones do. So if even tractor and trailer wires go to lamps from different 14 pole connectors the initiating signal should be the same. And it is the switch on the firewall.

Edited September 22, 2019 by Vladislav

[Vladislav]

Ok, the things could be more complicated indeed.

I found a picture of the blue parking brake knob and it has almost two electrical switches on it. There's one more air switch which is installed to the right from the throttle pedal in the cab, close to the heater core. It could be a low pressure indication but worth to be checked.

[JoeH]

Trucks typically use 2 air switches.

One kicks on below a certain pressure, this would typically be in a situation where your parking brake is kicked on, intentionally or in a low air situation.  Do not confuse this with the low air buzzer/light circuit. 

The other brake light switch is tied into the foot pedal and kicks on when there is air pressure going to the service brakes.

Recap: one is a positive pressure switch in the service brake air circuit, the other is a 0 air pressure switch in the Emergency (Park) air circuit. First is typically on the firewall, second is typically in the dash by the park knob.

Your situation sound more like a wiring issue than a switch issue, unless there's a 3rd switch for the trailer. But most of my work has been on straight trucks.  Good luck!

[JoeH]

Look for the trailer stop lamp switch in the dash, possibly T'ed into the air plumbing for one of the knobs.

My 2001 tractor may have had 3 knobs (I forget, it's been a few years since I sold it) 

one knob released truck park brakes,

Second knob supplied air to the trailer tanks,

Third knob released trailer park brakes.

One of my straight trucks had a 2 knob setup, one for trailer brakes, one for truck brakes.

[phildirt]

Issue is resolved.

There is a pressure switch outboard and forward from the treadle/ foot pedal valve. Corrosion from Pennsylvania salt, calcium, beet juice and other evil chemicals.

Required removal of primary fuel filter and fuel lines, 3 air lines to access.

Thanks for input.