Trailer lights hookup question
Thread Starter
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Junior User
Joined: Aug 2003
Posts: 79
Likes: 0
From: South Texas
Trailer lights hookup question
OK. We could not get the trailer lights to work when we hooked the trailer to the Bronco so we spliced off the original harness and tried to connect to the trailer connection without it. So the Bronco now has a the male connection to the trailer connected straight to it and then plugs into the trailer female.
Know everything works but the brake lights. When you step on the brakes the parking lights go out so now there is no light back there at all when you brake.
Anybody have any idea why this is happening?
Is it not possible to connect without the original trailer connection from the Bronco?
I am not understanding how the electric works and if there is something that original connection did to make the brake lights work.
Of course the problem could be with the trailer lights but what is the possiblility that both of them do the same thing when you brake. Turn off?
Know everything works but the brake lights. When you step on the brakes the parking lights go out so now there is no light back there at all when you brake.
Anybody have any idea why this is happening?
Is it not possible to connect without the original trailer connection from the Bronco?
I am not understanding how the electric works and if there is something that original connection did to make the brake lights work.
Of course the problem could be with the trailer lights but what is the possiblility that both of them do the same thing when you brake. Turn off?
Senior User
Joined: Sep 2004
Posts: 351
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From: Richfield MN
I take it that the Bronco never has had trailer hook up.
If it has any parts store has a adaptor that will work.
If no then when you hooked up your harness you got the wrong wire for brakes maybe.
to check use a simple 12volt tester "Its a has a 12 volt light with a clip on one end and a probe on the other side"
have some one step on the brakes and check your harness wiring.
"put the clip to a good ground and put probe on part of the plug of the harness you wired to the brake light"
If your light lights up its your trailer if not wiring is wrong.
If wiring is wrong go under the back of truck with somone holding down brake probe wires with tester untill you find the right wire.
If it has any parts store has a adaptor that will work.
If no then when you hooked up your harness you got the wrong wire for brakes maybe.
to check use a simple 12volt tester "Its a has a 12 volt light with a clip on one end and a probe on the other side"
have some one step on the brakes and check your harness wiring.
"put the clip to a good ground and put probe on part of the plug of the harness you wired to the brake light"
If your light lights up its your trailer if not wiring is wrong.
If wiring is wrong go under the back of truck with somone holding down brake probe wires with tester untill you find the right wire.
Thread Starter
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Junior User
Joined: Aug 2003
Posts: 79
Likes: 0
From: South Texas
What I did is hook up one of those little lights that tell you if your wires are correct. It lights up right for all even the brakes. And all work except for the brakes when you plug in the trailer.
What I think I need to know is if I did a major No no by removing the OEM trailer hook up and connecting the trailer wires dircect.
Does the OEM hookup do something to switch the brakes on that connecting straight can not?
What I think I need to know is if I did a major No no by removing the OEM trailer hook up and connecting the trailer wires dircect.
Does the OEM hookup do something to switch the brakes on that connecting straight can not?
Last edited by texashottie; Oct 1, 2004 at 05:20 PM.
Laughing Gas
Joined: Feb 2003
Posts: 877
Likes: 27
From: South Florida
Did you check the fuses ?
Did your Bronco come with a 7-pin harness plug on the rear? 
(its noted in the owners manuals....) If so there is a seperate set of fuses under the hood (driver's side) that provides power for all the functions of that 7-pin adapter. It may not have any fuses in the slots for the adapter. If the Bronco didn't come with that 7-pin from the factory (tow package) never mind.
Mike....... Miami, FL
(its noted in the owners manuals....) If so there is a seperate set of fuses under the hood (driver's side) that provides power for all the functions of that 7-pin adapter. It may not have any fuses in the slots for the adapter. If the Bronco didn't come with that 7-pin from the factory (tow package) never mind.Mike....... Miami, FL
Senior User
Joined: Jan 2004
Posts: 133
Likes: 0
From: Tucson,AZ
On a Bronco you have red turn signals and brake lights. What that means is your brake signal is on the same wire as your turn signals. So if your turn signals work on the trailer and the Bronco, then you know your wiring is ok. But when you step on the brakes and the running lights go out, (I assume only on the trailer) then it has to be a ground problem at the lights on the trailer or the ground on the trailer. 
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Elder User
Joined: Apr 2002
Posts: 813
Likes: 0
From: NJ
i also believe you have a ground problem. take a piece of wire and create a good ground and your problems should go away.
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