2021 Ram 3500 — Bulb Sizes (Headlight, Tail, Fog)

Quick reference

Notes

• 2021 Ram 3500 (fifth‑gen HD) was offered with multiple lighting packages. Tradesman/Big Horn most often shipped with halogen reflector headlamps and incandescent tails; Laramie, Longhorn, and Limited commonly have LED projector headlamps, LED fogs, and LED tail lamps. Dually clearance/cab lamps and tow‑mirror signal lamps may also be LED depending on package.
• Always verify by visual inspection: if you don’t see a removable socket behind the lens, it’s likely a sealed LED assembly.

LED vs halogen upgrade considerations

• CANBUS/BCM sensitivity: The Ram HD’s body control module monitors bulb current. Swapping to LED bulbs in halogen circuits (9005, H11, 7440/7444, 3157, 921, 194, 578) can trigger bulb‑out warnings, flicker, or hyperflash. Choose CANBUS‑ready LEDs or add load resistors where needed (especially front/rear turns).
• PWM headlight feed: The truck may pulse (PWM) the low/high beam circuits for DRL and bulb monitoring. Use LED headlight kits with built‑in decoders/anti‑flicker modules or add a dedicated anti‑flicker harness.
• Heat and fitment: High‑output LED or HID kits in halogen reflector housings can cause glare. For best beam pattern, use projector‑style retrofit housings or OEM LED assemblies. Check dust‑cap clearance and cooling space behind the lamp.
• Hyperflash on turns: If CANBUS LEDs don’t solve it, add 6–8 Ω, 50 W resistors in parallel at each turn signal circuit (front and/or rear) and mount resistors to metal away from wiring.
• LED tail/headlamp swaps: Trucks with factory LED assemblies use different connectors/modules. Converting from halogen to OEM LED often requires adapters and in some cases BCM coding via a scan tool.

How to replace each bulb

• Headlight low/high (H11/9005 halogen): Turn front wheels, open the fender‑liner access door, remove headlamp retaining bolts (Torx/10 mm), and slide the lamp forward. Twist the bulb counter‑clockwise to remove. Avoid touching glass.
• Fog light (H10/9145 halogen): Access from below or through the wheel liner; twist the bulb 1/4 turn. On LED fogs, the whole module must be replaced.
• DRL: On halogen trucks it’s the 9005 high‑beam bulb; replace as above.
• Front turn (7440/7444): Same headlamp removal as above; twist the amber socket to service the bulb.
• Tail/brake/turn (3157 incandescent tail lamps): Drop the tailgate, remove two Torx screws at lamp edge, pull the housing straight back off the clips, twist the socket(s), and replace the 3157 bulbs.
• Reverse (921): With tail lamp removed, service the white‑lens socket and install a 921/T15.
• License plate (194): Remove the two screws at the plate lamp, drop the lens, and pull the T10 wedge.
• Side marker (194 on incandescent lamps): Front marker is in the headlamp housing (service via headlamp removal). Rear marker is in the tail lamp (service with tail lamp removed). LED versions are sealed.
• Interior dome (578 festoon): Gently pry the overhead lens, release the festoon, and install a 41 mm 578. Verify polarity for LED.
• Interior map (194): Pry the map light lens carefully, pull the T10 wedge. Many higher trims use a non‑serviceable LED board.

Tip: Disconnect the negative battery cable when working around airbags or if replacing multiple exterior bulbs to avoid setting faults. Use dielectric grease on exterior bulb sockets to combat corrosion.

Common lighting issues for this generation

• Bulb‑out warnings/flicker after LED swaps due to CANBUS/PWM monitoring. Use CANBUS LEDs and, if needed, resistors/decoders.
• Moisture in halogen headlamps, especially after off‑road or car‑wash exposure; check vent caps and housing seals.
• Hyperflash from low‑draw LED front or rear turn bulbs; add resistors or program BCM where supported.
• Trailer lighting back‑feed confusing the BCM. Test with a trailer emulator or disconnect the 7‑pin during diagnosis.
• LED tail lamp outages on some trucks traced to internal module failure or BCM software; check for TSBs/recalls by VIN.
• Snow/ice accumulation on LED headlamps and fogs (they run cooler than halogen); use defrost or heated lamps if equipped.

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