Wiring Relays for High-Amperage Lights
Light bars and multi-pod setups can pull 20-40A. NEVER run that through a dash switch. Use a Bosch 40A relay (or pair of relays for 60A+ systems) triggered by a small dash switch.
Standard relay harness for one or two light bars:
Battery+ -> 30A inline fuse (within 12" of battery) -> heavy wire (10 AWG for 30A) -> relay terminal 30. Relay terminal 87 -> heavy wire -> light bar +. Light bar - -> chassis ground (clean to bare metal).
Relay coil: terminal 86 -> through 5A fuse -> dash switch -> ignition switched +12V (so the lights die when the key is off). Terminal 85 -> chassis ground.
For a bar pulling >35A continuous, use two 40A relays wired in parallel (split between two relays so each sees ~20A) or step up to a Hella 70A SPDT or solid-state relay.
Prefab harnesses save time: Rigid WHK-300, KC harnesses, or generic 'LED light bar wiring harness' on Amazon. They include the relay, fuse, switch, and pre-cut wire for under $25 — usually adequate for a single 200W bar.
CRITICAL: when wiring multiple high-amp loads (bar + ditch lights + rock lights), use a dedicated aux fuse block (see Blue Sea 5026 entry) rather than chaining everything off one battery terminal.
Why it works
- safe wiring for high-amp loads
- switch doesn't fail
Trade-offs
- another connection point if cheap parts
Tools required
- crimper
- wire strippers
- drill
- test light
Parts
| Part | Vendor | Est. price |
|---|---|---|
| Generic LED light bar wiring harness with relay | Amazon | ~$18 |
| Hella 70A SPDT relay | Hella | ~$22 |
| 10 AWG primary wire 25ft (red/black) | Del City | ~$25 |
Sources
Related
- Relay Basics - Bosch 5-Pin Wiring
- Auxiliary Fuse Block Installation (Blue Sea 5026)
- All Jeep Cherokee XJ guides & tools
- Browse the full DIY database
Written and maintained by an AZ wheeler and driveway wrencher. How we source guides. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.