Brake lights are out but Cyclops brakelight works - Diesel Forum

rea2112 · 08-26-2005, 12:35 PM

I found out that my brake lights are out. The cyclops brake light on the roof works fine. I also have a skull in the receiver hitch and the tail lights work but the brakes don't light up the eyes. I'm using the 4 pin tow connector for this. I unplugged the skull and same problem. Per the manual I have checked like 4 fuses. Anything that mentioned brakes I checked. Only found that the Tow battery charger 20a fuse was blown. temporarily put in the Seat heater 30a fuse and that did not make a difference.
Any ideas? I'm good with electronics but I'm stumped here.
primarily because the cyclops brake light works.
I highly doubt both brake lights and the 2 lights for the Skull eyes have burned out. I have not confirmed that the 7 pin brake connector has 12 volts when the brake is applied. Will do that today.
I was also having difficulty getting the tail light assembly out. 2 screws in the tailgate jamb area but I didn't want to pull to hard after they were out. Ford service dealer says you need to hank real hard cause they are mounted on studs on the opposite end of the screw side. Thanks for any input. Mostly want to know if this has happened to anyone else's truck. FYI: Tail lights (parking) and blinkers work fine.

rcdallas · 08-26-2005, 01:51 PM

[ QUOTE ]
I found out that my brake lights are out. The cyclops brake light on the roof works fine. I also have a skull in the receiver hitch and the tail lights work but the brakes don't light up the eyes. I'm using the 4 pin tow connector for this. I unplugged the skull and same problem. Per the manual I have checked like 4 fuses. Anything that mentioned brakes I checked. Only found that the Tow battery charger 20a fuse was blown. temporarily put in the Seat heater 30a fuse and that did not make a difference.
Any ideas? I'm good with electronics but I'm stumped here.
primarily because the cyclops brake light works.
I highly doubt both brake lights and the 2 lights for the Skull eyes have burned out. I have not confirmed that the 7 pin brake connector has 12 volts when the brake is applied. Will do that today.
I was also having difficulty getting the tail light assembly out. 2 screws in the tailgate jamb area but I didn't want to pull to hard after they were out. Ford service dealer says you need to hank real hard cause they are mounted on studs on the opposite end of the screw side. Thanks for any input. Mostly want to know if this has happened to anyone else's truck. FYI: Tail lights (parking) and blinkers work fine.

[/ QUOTE ]

As far as why your optional reciever brake light you have plugged into the trailer plug that is on a different circuit from your trucks main brake lights, they do this so that if you have a short in your trailer, you don't loose lights on your vehicle.

I like to keep things simple. I learned this early as I am a electrician.

First off make sure your fuses work. ie continuity.

Physically check to see if you have power to each tail light, get yourself a 12v dummy light. Physically check your getting 12v to each end of the fuse, it's much easier to do this vs pulling each fuse and looking at it.

Any other aftermarket stuff that required you to splice into 12v, make sure those connections are fine, as just last week my cousin's Ranger didn't have tail lights due to the fact his aftermarket stereo the illumination wiring had a dead path to ground.

Again, keep it simple verify voltage to the tail lights, and make sure their is continuity between the fuses. If all ok, then you can start tracing back the harness from the engine compartment along the frame rail all the way to the rear for anything out of the ordinary.

Now if you have power to everything, look at the bulbs; it's possible they could have gone out at the same time, they come from the factory brand new at the same time.

All in all you'll get it; just take your time, don't jump from one step to another without doing the first step completly. Stranger things have happened.

jsglick · 08-26-2005, 04:18 PM

Not to get to deep on you, but the “high mounted stop lamp” gets its power directly from the brake pedal switch. All other stop lamps ( rear and trailer) get their power from the brake pedal switch through the “multifunction switch”. The only fuse is F2-34. From the multifunction switch the line goes to many places including PCM , rear lamps, and several other points. Could be the turn signal switch (multifunction) might be bad.

PoppaSmurf · 08-26-2005, 09:53 PM

Also double check your bulbs, and the socket in which they plug into. Never assume anything, check everything. Good luck.

gooseguide · 08-26-2005, 10:15 PM

If your turn signals are out also, I would suggest checking the turn signal switch.

Just had the same problem with my 150

Keith

ritschner · 08-27-2005, 12:53 PM

I was towing a fifth wheel once when I noticed I had trailer brakes. Pulled over to check and found out the brake lights on the truck were out also. It turns out the brake light switch on the brake pedal arm had overheated and distorted enough to cause brake light failure and also loss of signal to the brake controller. No short, no blown fuses, just a part failure. I carry a spare now, hate to lose trailer brakes when towing.