tow lights not working properly

Reply Subscribe

Thread Tools

Search this Thread

May 28, 2008 | 04:42 PM

DanK5

Thread Starter

Junior User

Joined: Jan 2008

Posts: 72

Likes: 0

From: Memphis, TN

tow lights not working properly

What I got-
99 F150 4.6 with factory tow package.
Cheapo set of magetic towlights
Have the round ford plug that the flat 4 pin tow lights plug into.

BREAK DOWN-
With Parking Lights OFF

Blinkers, Work

Brake Lights, Work but only 50% as bright as they should be.

Flashers, Work but only 50% as bright as they should be.

Parking Lights ON

Blinkers, No cuz the lights come on at 100% brightness.

Brake Lights, No cuz the lights come at at 100% brightness.

Flashers, No cuz same reason.

In other words: I can hold the brake on and the lights come on at 50% brightness, turn the parking lights on and they go 100% brightness.
They SHOULD be 100% brightness each time the brake is applied.
I have checked all fuses and relays- swapped one relay with another and no change.

Any help would be appreciated.

Thanks, Dan

May 28, 2008 | 05:17 PM

BPofMD

FTE Legend

Joined: Jul 2005

Posts: 65,938

Likes: 1,432

From: Millersville, MD

Sounds like the wiring on the trailer plug has the brake light/tail light wires backwards. Should be dim with parking lights/running lights on and bright with brakes.

May 29, 2008 | 12:55 PM

rbaker6336

Post Fiend

Joined: Feb 2007

Posts: 7,191

Likes: 4

From: Blairsville,Ga

if wiring is corect your not getting a good ground

May 29, 2008 | 01:12 PM

BPofMD

FTE Legend

Joined: Jul 2005

Posts: 65,938

Likes: 1,432

From: Millersville, MD

He is correct...if you are relying on the attachment of the ball mount for a ground, DON'T. Insure the plug's ground wire goes through to the trailer also!

Jun 1, 2008 | 08:00 PM

fasthauler

Fleet Mechanic

Joined: Mar 2004

Posts: 1,398

Likes: 17

From: Hesperia, CA

I stand by the ground issue as well. Most of the trailer wiring issues I have seen are ground problems. But BPofMD could be right about the tail and brake lights being backwards.

Jun 1, 2008 | 09:31 PM

projectSHO89

Hotshot

Joined: Jan 2004

Posts: 19,762

Likes: 1,079

From: St Louis

The tail lamps and the brake lights on the trailler are the same. They are not separate. For brake lights, the system simply turns on both lamps at the same time.

All circuits share the common ground which has already been pointed out.

The running lamps are a separate circuit

Steve

Jun 2, 2008 | 12:36 AM

fasthauler

Fleet Mechanic

Joined: Mar 2004

Posts: 1,398

Likes: 17

From: Hesperia, CA

Yes you are correct they are the same bulbs, but they are dual filaments and the brake and turn signal part of the filament is 50 percent brighter than the taillight filament. As BpofMD was trying to point out, if the wires for the taillight circuit was in fact hooked to the brake light filament instead of the taillight filament then the taillights would be twice as bright as the brake/turn signal filaments. Thus, if the taillights were on you wouldn't see the turn signal or brake lights when they were applied because the brilliance of the taillights would over ride them. But you would see them at 50 percent brilliance when the taillights were turned off. The running lamps and the taillights are the same circuit. The turn signals/brakes are a seperate circuit. With the symptoms described this sounds like the logical problem.