Marker lights under tailgate

SLittle

Registered User
Joined
Sep 4, 2018
Posts
51
Reaction score
19
Location
Iowa
1991 F350 Dually

Under the tailgate yet above the bumper are three red marker lights. They haven't worked since I've owned the truck.

Replaced the lights with some LED markers but there isn't any power to the lights. The rear fender marker lights do not have power either.

Without troubleshooting the entire harness, I think it would be much easier to just splice wiring in to my trailer plug.

So these lights under the tailgate.... were they on with the tail lights or on with the brake lights?

(On anytime the headlights are on or only on when you press the brake?)
 

Kizer

Supporting Member
Supporting Member
Joined
Mar 22, 2007
Posts
722
Reaction score
291
Location
Denton, Texas
They are supposed to come on with your running lights.
I don't have a diagram in front of me but I believe that's a brown wire.
 

SLittle

Registered User
Joined
Sep 4, 2018
Posts
51
Reaction score
19
Location
Iowa
They are supposed to come on with your running lights.
I don't have a diagram in front of me but I believe that's a brown wire.

Yup. Marker / tail lights is brown wire in trailer wiring. I'll just tap that wire for all the fender and tailgate lights. Thanks.
 

chillman88

Supporting Member
Supporting Member
Joined
Feb 22, 2017
Posts
6,022
Reaction score
6,152
Location
Central NY
Check the trailer relay under the hood by the brake booster. That powers the lights under the tailgate and the fender markers. Been there myself on my truck.
 

snicklas

6.0 and Loving It!!
Staff member
Joined
Aug 7, 2006
Posts
6,164
Reaction score
2,342
Location
Greenfield, Indiana
Make sure the trailer lighting relain in place. On the dually trucks, the power for those lights is supplied by the trailer relay.
 

SLittle

Registered User
Joined
Sep 4, 2018
Posts
51
Reaction score
19
Location
Iowa
Check the trailer relay under the hood by the brake booster. That powers the lights under the tailgate and the fender markers. Been there myself on my truck.

Make sure the trailer lighting relain in place. On the dually trucks, the power for those lights is supplied by the trailer relay.

Looks like previous owner bypassed the trailer relay???? The trailer plug is spliced in to the tail lights and the brake controller is an aftermarket add on.
 

chillman88

Supporting Member
Supporting Member
Joined
Feb 22, 2017
Posts
6,022
Reaction score
6,152
Location
Central NY
Looks like previous owner bypassed the trailer relay???? The trailer plug is spliced in to the tail lights and the brake controller is an aftermarket add on.

Check the relay anyway. That could even be why they bypassed it. Mine was bad when I bought the truck, and the mounting bracket was missing. Replaced it and not being properly mounted it got water in it and stuck on. Then I got smart and replaced it with a standard Bosch style relay and screwed it to the fender.

This is what the stock relay looks like:

img_20190505_140950527-jpg.122257


Here's my personal fix:

img_20190505_140545797-jpg.122258

img_20190505_141212310-jpg.122259
 

Latest posts

Forum statistics

Threads
91,217
Posts
1,128,503
Members
24,045
Latest member
Ramtough01
Top