How do the brake lights get their signal?

[Mr Z]

Can someone please explain to me how the brake lights get their signal and which light they share (turn or running lights)?

There are three rectangular lights in each of our tail light housings:

The Outer (Turn Signal with a dual filament bulb)
The Middle (Reverse with a single filament bulb)
The Inner (Running light with a dual filament bulb)

When I connect the TV the turn signals work, the reverse works and the running lights are all on. When I step on the brake the TV lights illuminate and I can hear the 6 brake magnets humming but I don't have any brake lights on the Airstream.

After pouring over the schematics I noticed there isn't a connection between the blue brake wire and the tail lights. My question is do I make a jumper between the blue brake wire and the turn signal wires (Brown and Red wires in our trailer)?

Any help would really be appreciated.

[John Ware]

The blue wire is for the brakes only, the brake lights are on a separate wire. The brown wire should be the marker (tail)lights and the red wire is the auxiliary(+) wire. When you see a dual filament bulb, the long one is for tail lights and the short one is for turn signal and or brake lights. Ck to see if the white wire(-) is properly grounded.

[bweybright]

May I ask what you are wiring? Most modern connections take care of the connections and wire routing. So I am not sure what you are trying to wire?


This reminds me of my grandad working to wire up the boat trailer for winter in Florida from Michigan in 1962?....where I learned to curse.

[richard5933]

You do not need a jumper, nor should you install one.

The brake lights should come on in the trailer when you press the brake pedal in the TV. My guess is that your TV's 7-wire harness is not wired correctly.

If I remember correctly, the left and right turn lights in the trailer serve double duty as the brake lights. The TV has to send the correct signal through the harness for these to function. You can test your TV's wiring with a multimeter - have a helper press the brake pedal (or shove a stick between the seat and pedal to hold it down) while you measure at the 7-wire harness to see if your TV is sending a brake light signal to the trailer.

Not uncommon for a TV to have the trailer lights wired incorrectly or incompletely. What is the make/model/year of your TV? I'm sure that someone will be familiar with the wiring.

[Bill M.]

What is the TV? Is it American? Does the TV use the dual filament bulbs?. I had to buy a special brake light converter to hook my Volvo to a boat trailer.

[tjdonahoe]

Turn signals and brake lights use a common wire…thru the turn signal switch

[JCWDCW]

Best idea is to check the power at the TV umbilical
Lots of good and correct info already given
I also use a stick between the seat and brake pedal then move seat forward to engage the brakes.
Buy a simple check light from the automotive section. It has a probe and an alligator clip. Ground the clip and use the probe to check for power Much easier to trouble shoot intermittent voltage like turn signals
If your 4-ways work then usually the brake circuit works.. except on my Dakota where the brake light fuse was blown.
Best the check brake lights separately but that is easy if you see the reflection of the brakes in the aluminum trailer

[richard5933]

Originally Posted by tjdonahoe

Turn signals and brake lights use a common wire…thru the turn signal switch

There are some vehicles which use a separate circuit for brake lights and turn signals, which is why they make these: https://www.carid.com/roadmaster/3-t...B#installation

[Mr Z]

Oh I agree that its most likely the wiring from the TV since I'm the fool that made it!
The TV is a 2002 E-350 Super Duty. Its an Ambulance van ordered from Ford as a "Stripped Chassis" which means all of the wiring that would have traveled to the rear of the vehicle was terminated in plugs under the front driver's side dash.
I found the brown plug for the brake controller and the grey plug which has all of the wiring from the tow package relays and ran a trailer appropriate plug to the rear bumper with a 7 pin receiver for the Airstream plug.

Now I need to know which of the dual filament bulbs carried the brake signal in the Airstream. Is it the outer light with the turn signal or the inner light with the running lights.
According to tjdonahue it sounds like its the turn signal light.

According to the schematic and visual check the tail lights (except the Reverse) each tie in with a GREEN wire which is the Tail Clearance Light and a RED or BROWN wire (depending on Left or Right) which is the Turn Signal wire.




And as I'm typing all this I see that richard5933 might have my solution..

[richard5933]

Originally Posted by Mr Z

Oh I agree that its most likely the wiring from the TV since I'm the fool that made it!
The TV is a 2002 E-350 Super Duty. Its an Ambulance van ordered from Ford as a "Stripped Chassis" which means all of the wiring that would have traveled to the rear of the vehicle was terminated in plugs under the front driver's side dash.
I found the brown plug for the brake controller and the grey plug which has all of the wiring from the tow package relays and ran a trailer appropriate plug to the rear bumper with a 7 pin receiver for the Airstream plug.

Now I need to know which of the dual filament bulbs carried the brake signal in the Airstream. Is it the outer light with the turn signal or the inner light with the running lights.
According to tjdonahue it sounds like its the turn signal light.

According to the schematic and visual check the tail lights (except the Reverse) each tie in with a GREEN wire which is the Tail Clearance Light and a RED or BROWN wire (depending on Left or Right) which is the Turn Signal wire.
Attachment 416202

Attachment 416203

And as I'm typing all this I see that richard5933 might have my solution..

Definitely the turn signal and brake light share a filament. The dimmer one if for running lights.

[Wazbro]

Originally Posted by Mr Z

And as I'm typing all this I see that richard5933 might have my solution..

NOTE; That device gets a connection from separate brake light wire on TV (not a wire common with turn signal). Not the connection from brake controller that goes to trailer brakes, that is only to activate breaks and has a range of power going through it.

[Mr Z]

Wazbro- I'm really glad you mentioned that.

My plan is to mount the Brite Lite under the front dash or driver's seat and tie into the brake signal wire off of the pedal and then splice into the sending wires for the turn signals.

Has anyone else installed one of these that has a better idea or does this sound feasible?

And thanks to everyone for all the replies and help.

[Wazbro]

Originally Posted by Mr Z

Wazbro- I'm really glad you mentioned that.

My plan is to mount the Brite Lite under the front dash or driver's seat and tie into the brake signal wire off of the pedal and then splice into the sending wires for the turn signals.

Has anyone else installed one of these that has a better idea or does this sound feasible?

And thanks to everyone for all the replies and help.

That sounds like it should work. I haven't installed a generic one. Just a vehicle specific one, that was easy unplug wiring harness for lights on back of vehicle from main harness and plug adapter in in between.