I re-wired a trailer. Everything now works except . . . when I turned on the headlights, the brake lights don't come on. They work when the headlights aren't on, but not when they are on.

Help!

What happens when you turn on the four way flashers with and without the headlights on? What about the turn signals with and without the headlights?

Sounds like possible you have the brake lights and the running lights wired onto the same circuit somehow? Are the taillights as bright as the brake lights? They should be noticeable dimmer.

Just to refresh Brown is for running lights, Yellow is left turn/stop, green is right turn/stop, white is ground.

I posted earlier about a need for a sticky/locked topic on this. Such a common issue, and the results are always about the same. Wiring on a trailer is such a basic circuit, but most folks aren't savvy about this.

Make sure you have a good ground to the truck

I would be surprised if it is a ground issue (I'll probably eat my words now). If it where a ground issue I would expect something like all the lights go out when stepping on the brakes or all the lights blink when the left turn signal is on or the dash lights come on when stepping on the brakes with the lights off (I just had a car with this symptom the other day and it was a ground issue with the taillights). Grounds will typically give you strange problems. Power supply issues are generally straight forward, This doesn't work when I do this.

You most likely spliced into the wrong wire somewhere. Could be a ground issue, but I would bank money on otherwise.

I'd check the wiring and make sure it is installed the way airjer suggested....I think a sticky for trailer lights would be essential for the FM boards. Or maybe go as far as a How-To section that could cover boating repair/maintenance. It's an all-too common issue that can really put a damper on fishing plans. Get out and enjoy the weather this weekend!

Marineman you have mail.

Thanks for all of the replies. I have the three female and one male flat wire harness (4 pin) with the 5 channel going to the Silverado. The trailer has the yellow/brown, green/brown and the white wire. The white wire is grounded to a screw on the trailer. On the driver's side trailer light, the yellow wire pushes into where it specifies to go (turn.stop) and the brown pushes into where it says to go (tail). On the passenger side trailer light, the green pushes into where specifies (stop/turn) and the brown where specified (tail). I rechecked connections to the lights and splices. There's two holes where you can push in the sire to connect for each turn and trailer connection - but I don't think it matters where you push in the single wire(?).

Both turn signals work when headlights are on or off. Brake lights work when headlights are off. When I turn on the headlights the trailer lights also work. The only thing that doesn't work - brake lights don't come on when the headlights are on.

You officially have me stumped!

Did you try the four way flashers? Since the brake is essentially the same as having both the blinkers on at the same time I am curious to see if the four ways work with the lights on.

Did you happen to notice if the turn signals blink in sinc with the vehicle or opposite?

Hey Shorelunch...did you figure out your problem with the lights? Cause when you do let me know. I have the exact same problem, only it is only my left brake light that goes out when I have the lights on. All the lights work fine when the vehicle lights are off????

Well . . . when I installed and then tested my lights, everything worked except for the brake lights when I turned on the headlights.

I hooked up the trailer to the truck two nights ago and everything worked as it should. When they weren't working, I manually turned on the headlines. When they worked the other night, the headlights were on "auto". Heck if I know . . . but the brake lights work when it's on "auto."

It was dark when you did this, and your headlights came on, right?

If you run into problems again I'd check you truck out with a test light - see if you're getting the proper output from your pickup (with the trailer disconnected) first. I'm guessing the issue resides with your pickup and the trailer connector & it's connections.

marine_man

My Blazer has the same thing with the lights. They come on automatically when the vehicle is started. The lights work great when I don't manually turn them on. But when I do, the left brake light goes out when the pedal is pushed??? The right light works fine.

I was thinking I'll just not turn on my lights at night and just use the automatic lights, but the only problem with that is the dash lights don't come on then.

Any ideas?

Have you checked the output on your pickup at the flat 4 pin connector? See how things are functioning there -

Brown = Taillights
Yellow = Left Turn Signal
Green = Right Turn Signal
Green & Yellow at the same time = brakes

Start with that and let's make sure it's the boat trailer and not the pickup.

marine_man