How to wire running lights on tow mirrors

Adding running lights to aftermarket tow mirrors means feeding the mirror’s LED a constant 12V signal from the tow vehicle’s running light circuit and combining it with the existing turn signal feed so the LED can do both jobs. The standard kit (Boost Auto Parts dual-function harness, Recon, Diode Dynamics, or similar) bundles two modules, two T-taps, and two jumpers. Plan on 2 to 3 hours for both mirrors on a GM truck if you have not pulled mirror shrouds before.

This works on aftermarket telescoping tow mirrors for Chevrolet Silverado 1500/2500/3500 and GMC Sierra 1500/2500/3500 from 1988 through 2019. The same wiring concept applies to aftermarket mirrors on Ford and Ram trucks, but the wire colors and module placement differ.

Parts you need

• Dual-function (signal and running light) wiring harness kit for your mirror style. Match the kit to whether your mirror LEDs are dotted or stripped, the two style options most aftermarket mirrors come in.
• The kit includes: two LED running light feeds with inline fuses, two combiner modules, two T-taps, and two disconnect jumpers.

Tools

• Wire strippers and cutters.
• Crimp pliers.
• Phillips head screwdriver.
• Flathead screwdriver.
• Heat gun (or lighter, but heat gun is safer for shrink connectors).
• Pliers.

The job is easier with both mirrors off the truck on a workbench. Most aftermarket tow mirrors unbolt at the door with three or four Phillips or Torx screws and a wiring connector. About 10 minutes per side to remove.

Step 1: Mirror disassembly

Top arm cover. Each tow mirror has two telescoping arms running from the door mount to the mirror head. Place the mirror on a workbench, extend the arms, and find the small indentation on the underside of the upper arm cover near the head. Pry the cover up with a flathead at that point and lift it off.

Mirror glass. Most aftermarket tow mirrors have an upper main glass and a lower spotter glass. With the upper glass in the fold-down position, grasp the lower glass and pull it up out of its retainer. Then fold the upper glass up, slide both hands under the lower edge, and pry it out with steady pressure on both sides. Disconnect the defrost and signal connectors at the back of the glass before fully removing it (if your mirror has them).

Top cap (shroud). Four Phillips screws in each corner. Remove all four, lift the cap off, and disconnect the reverse light connector on the underside.

Step 2: Install the running light module

Cut the front marker light connector. Find the marker light wire (the small LED on the front-facing edge of the mirror) and cut its connector off, leaving 2 inches of wire on the connector side. Keep the connector, you will use it.

Route the running light wire. The kit provides a long wire with an inline fuse on one end and a stripped end on the other. The stripped (no-fuse) end goes into the mirror head. Feed it from the door-side base of the mount, up through the lower arm, through the upper arm, into the mirror head. Leave several inches of slack inside the head.

Identify the turn signal wire on the existing mirror harness. This is usually blue on GM aftermarket mirrors, but always confirm with your specific mirror’s manual. Strip the end.

Cut the marker light’s ground wire. You will use this for the disconnect jumper later.

Connect the module. The module has two input wires and one output wire. The two-input side has one wire that matches the running light feed (typically orange) and one that matches the turn signal feed (typically blue). The single output wire (typically orange) feeds the LED.

• Orange running light feed (from the cab) -> orange input on the module.
• Blue turn signal feed (from the mirror harness) -> blue input on the module.
• Orange output -> the front marker light connector you cut earlier (the power wire).

Crimp and shrink each connection.

Disconnect jumper. Take the black inline splice (disconnect jumper), crimp it onto the ground wire of the marker light connector. Then plug the front marker light connector back into the LED.

T-tap to ground. Find the reverse light’s ground wire (usually gray). Place the wire into the T-tap, close it until it clicks. Plug the disconnect jumper’s other end into the T-tap. This grounds the LED.

Heat shrink everything. Apply a heat gun until the adhesive squeezes out of each butt connector. Tuck the module into the mirror head out of the way of the top cap’s screw locations.

Step 3: Reassemble the mirror

Plug the reverse light connector back into the top cap. Pull the glass signal and defrost wires through the cap, then reinstall the top cap with its four Phillips screws.

Click the glass back in by pressing firmly until it seats. Listen for the click.

Reinstall the upper arm cover, making sure the running light wire runs along the existing harness inside the arm and does not bind. Do not pull slack out of the arms, the slack lets the arms telescope without straining the wire.

Install the mirror back on the truck. Feed the long end of the running light wire through the door’s wiring grommet into the cab.

Step 4: Tap the running light circuit

Inside the cab, you need a 12V source that turns on with the tow vehicle’s running lights. Options:

• T-tap to the running light wire at the fuse panel.
• Tap to the dash’s parking light circuit.
• Use a fuse-tap on the parking light fuse.

For most GM trucks 1999 to 2019, the easiest tap is at the BCM or the fuse panel under the dash. Look for the wire that powers the dashboard’s tail/marker lights. Confirm with a multimeter, the wire should be 0V with parking lights off and 12V with them on.

Splice the running light wire’s inline-fuse end into the tap. Make sure the inline fuse is the one in the kit, do not bypass it.

Step 5: Test

Turn the parking/running lights on. The mirror’s LED should illuminate at running-light intensity. Activate the turn signals: the LED should blink at full brightness. Brake pedal: the LED should not respond unless your kit specifies brake light function (most do not). Run through hazards, headlights on, and headlights off cycles to confirm everything switches correctly.

Repeat the entire procedure for the second mirror.

Reverse and puddle lights

Most GM tow mirrors include parking lights wired through the factory harness, so you do not need additional kits for those. To add reverse and puddle lights:

• Use a Boost Auto Parts dual-function dome and reverse harness or equivalent.
• The kit has two modules with two orange inputs and one blue output each.
• Tap the truck’s reverse light circuit at the fuse panel (one of the input wires).
• Tap the puddle light circuit at the panel (the other input).
• The output drives the LED in the mirror.

The wiring concept is the same as the running light install. Crimp, shrink, and tuck.

Common installation mistakes

• Pulling slack out of the mirror’s telescoping arms during reassembly. The arms cannot extend without straining and breaking the wire.
• Skipping the inline fuse on the running light feed. A short in the mirror head can take out the truck’s parking light circuit and any other accessory on that fuse.
• T-tapping to a switched-with-ignition wire instead of the constant-when-parking-lights-on wire. The LEDs go out when you start the truck. Wrong tap.
• Using non-adhesive butt connectors. Mirrors get wet inside. Adhesive heat-shrink is the standard.