How to Install a Headlight Wire Harness for 2015–2026 Ford Mustang

Installing a headlight wire harness is a common and very useful upgrade when fitting aftermarket headlights (LED or HID) on Mustangs. Below we split step-by-step instructions by generation. 2010–2012, 2015–2017, and 2018–2023 and add practical notes for the newest 2024–2026 models. The step details are adapted from the official installation guides.

Safety first: always disconnect the negative battery terminal before starting, keep hardware organized, and if wiring the DRL harness, use a fuse-tap on a switched fuse (details below). Do NOT use dielectric or weather-sealing grease on connectors.

Tools & Materials

• Headlight/DRL wire harness kit (model-specific)
• Socket set (8mm, 10mm, 13mm, 7/32" where required)
• Power ratchet (optional) & 1/4" ratchet
• Flat screwdriver & panel popper / trim tool
• Zip ties, electrical tape or heat shrink
• Fuse tap (recommended) & multimeter (optional)

These are the tools called out in the guides.

Overview of the Steps (common to all generations)

High level: disconnect battery → remove protective covers / bumper (if needed) → remove OEM headlight assemblies → install harness and new headlights → test functions → aim and reassemble. Below are generation-specific, step-by-step instructions.

For 2010–2012 Mustangs

These earlier S197 Mustangs require a few different fasteners and more bumper access. Follow these steps precisely so clips are not broken.

1. Disconnect battery. Remove negative battery terminal to avoid shorts.
2. Remove upper shield / grille cover. Remove the plastic mount clips that hold the upper shield and center grille; set the shield aside.
3. Remove front bumper (partial removal to access headlight bolts).
   • Remove the 2 × 8mm bolts along the top of the bumper/grille.
   • Unscrew the two 7mm bolts in each wheel well that secure the bumper flange.
   • Unscrew the 4 × 7mm bolts under the front bumper.
   • Carefully pull the bumper outward at the corners to release the mounting clips — you usually don't need to fully remove the bumper, just create enough clearance to reach headlight bolts.

   Take care to remove the clips gently — forced removal can break plastic retainers.

4. Remove headlight bolts and assembly.
   • Remove the three 8mm bolts securing each headlight (top + sides as shown in the manual).
   • Gently pull the headlight assembly outward (there's a plastic tab to release). Unplug the OEM connectors and remove the turn-signal socket/bulb from the old housing.
5. Install the DRL / power harness.
   • With both headlights removed, route the DRL harness through the engine bay toward the passenger fuse box (kick panel area).
   • Connect the harness: red to battery positive, black to battery negative. For the switched (grey) DRL trigger wire, tap into a switched 5A fuse using a fuse-tap (do not hard-splice). Tapping a 5A circuit for DRL power — confirm with a multimeter and the vehicle fuse diagram first.
   • Secure harness with zip ties away from hot or moving parts.
6. Plug, mount, and secure the new headlight. Plug the new headlight sockets into the vehicle harness (and the DRL connector if required). Position the headlight into the bumper, align mounting points and hand-thread bolts, then torque snugly.
7. Reassemble bumper and covers. Reverse bumper removal steps, reinstall clips, bolts, upper shield.
8. Test & aim. Reconnect the negative battery terminal, test low/high beams, DRLs, turn signals and any animations. Adjust aim by parking ~25 ft from a wall and turning the adjustment screws clockwise to lower and counterclockwise to raise.

For 2015–2017 Mustangs

2015–2017 (S550 early) headlight removal and harness routing follows official guidance — below are the practical steps with exact fastener notes.

1. Disconnect negative battery terminal.
2. Remove radiator shroud / top cover. Use a panel popper to remove plastic push pins holding the radiator shroud cover; lift the cover off and set aside to expose top bumper fasteners.
3. Remove front bumper (to access headlight fasteners).
   • Remove the 6 × 8mm bolts and 2 × (7/32") bolts at the top of the grille.
   • Remove the inner bumper bolts/nuts from behind the bumper — use a panel popper to take out the 3 plastic retainers and open the plastic cover to reach inner fasteners.
   • For 2015–2017 specifically: remove 2 × 8mm bolts from the inside (one per side) that secure the bumper to the frame. Gently pull down then outward on the bumper corners to release the clips and create work space.
4. Remove headlight bolts.
   • Remove the 2 × 10mm bolts (top and bottom) that secure the headlight.
   • Remove the 13mm bolt on the side of the headlight (this often secures the inner mount).
   • Lift the housing outward, unplug vehicle connectors and the turn signal socket, and remove the OEM assembly.
5. Wire the DRL harness & plug the harnesses.
   • Find the included turn signal / DRL harness in your aftermarket kit and plug the harness into the vehicle turn-signal connector and the new headlight's socket (follow the harness color coding).
   • If your harness includes a DRL harness, route the grey (trigger) wire through the firewall to the passenger fuse box and tap into a switched fuse. Secure the harness with zip ties.
6. Mount the new headlight & reassemble. Slide the new headlight into position, reinstall the bolts (hand-tighten then torque), return the bumper and radiator shroud to their original positions and resecure all clips/bolts.
7. Test & aim. Reconnect battery, test every function (low, high, DRL, turn signal). If any function is inactive, verify the plugged connectors, ground points, and the tapped fuse. Adjust aim from ~25 feet away.

For 2018–2023 Mustangs

The 2018–2023 models follow the same overall procedure as 2015–2017 but have one key difference in bumper inner fasteners — the inner bumper bolts use a larger fastener. The removal/access pattern is identical but note the inner bolt sizes.

1. Disconnect negative battery terminal.
2. Remove radiator shroud and top cover. Pop the plastic push pins and lift the shroud to expose the top bumper hardware.
3. Remove front bumper (carefully).
   • Remove 6 × 8mm bolts and 2 × (7/32") bolts from the top of the grille.
   • Remove inner bumper fasteners — use a panel popper for plastic retainers and open the access cover.
   • For 2018–2023: remove the 2 × 10mm bolts inside (note: 10mm vs 8mm on earlier models). Then gently separate the bumper cover to reach the headlight mounting bolts.
4. Remove the headlight assembly. Remove the 2 × 10mm top/bottom headlight bolts, then the 13mm side bolt; unplug connectors and lift out the assembly.
5. Install harness & headlights.
   • Plug the included turn signal harness into the vehicle connector and into the headlight harness (match white/yellow wires per the kit guide).
   • Route and secure the DRL harness. If the harness has a grey wire for ignition-switched DRL, tap it to a switched fuse (a fuse-tap is recommended). Use zip ties and keep wires away from heat and moving parts.
6. Reassemble & test. Reinstall the headlight bolts, reattach the bumper and shroud, reconnect the battery and test all functions. Final aim adjustment is recommended.

Notes for 2024–2026 Mustangs (S650 and later)

The 2024+ Mustangs use the next-generation body and lighting architecture. While the overall workflow (disconnect battery → remove covers/trim as needed → remove headlight bolts → install harness → test → aim) is still the same, exact fastener locations and the need to remove the bumper can differ by trim and bumper style. For 2024–2026 specific headlight products, follow the installation instructions included with the headlight kit for your exact model.

If a product's install instructions are not available online, ask the product supplier for the printable manual or request professional installation — many shops will do this quickly and safely.

Common Troubleshooting & Tips

Where to Get Mustang Headlights

We stock a wide range of Mustang lighting solutions and compatible harnesses. Browse by generation:

• Mustang headlights & tail lights (all generations)
• 2015–2017 Mustang headlights
• 2018–2023 Mustang headlights
• 2024–2026 Mustang headlights

Final Safety Reminders

• Always disconnect the negative battery terminal before working on electrical systems.
• Do not use dielectric or weather-sealing grease on connectors — this can cause connection problems and void warranties.
• When tapping fuses for DRLs, use a fused tap and choose a correct switched circuit — if unsure, consult the vehicle fuse diagram or a pro.

Need installation help?

If you want, we can recommend a shop or help you find a model-specific installation manual for the headlights you purchase on ClutchBlaze. For all the mistang lighting products, visit our Mustang collection.