Tow electrical marker lights not working

LMASSMAN

MEMBER
2013 TOYOTA TACOMA
6 CYL
TURBO
4WD
AUTOMATIC
260,000 MILES

Marker lights not working on the truck and towed trailer has no marker lights. All other lights work; brakes and turn signals work. The brake controller (Tekomsha P3 with harness) LED doesn't not light up any more. Checked fuses all 30 amp fuses in main box that relate to Brake of Tow all show good. Checked fuses on drive side in cab all good. Replaced one burnt out bulb on driver left front marker. Still no marker lights on trailer. License plate lights work on main head lights on.

Any more places to check?

1 Reply

STEVE W.

MECHANIC
13,004 POSTS

Do the marker lights on the truck work if the trailer is unplugged? Does the truck have a factory tow package or did someone add the wiring and harness? You say the plate lamps work, is that only with the headlights on or do the work in the marker light position as well?
Do you have the LED style rear lights?
Looking at the wiring diagrams it looks like the truck with a tow package used relays to take the load off of the power panel and body control module. The one without could have burnt out the BCM driver for the tail lights if the trailer wiring was connected directly to the circuit.
As a test take a test light make sure it is connected to a good ground, then with the key on and lights off test all of the fuses both under the hood and in the dash fuse box. You just touch the light to the tabs on top of each fuse and check that voltage is actually getting to the fuse and to both sides of it.