{"product_id":"the-relay-loom-h4-bi-xenon-headlight-wiring-harness-pair","title":"The Relay Loom | H4 Bi-Xenon Headlight Wiring Harness Pair","description":"\u003cdiv class=\"product-narrative\"\u003e\n\u003cp\u003eA headlight upgrade that flickers is worse than no upgrade at all. The bulb is rarely the culprit. In most H4 conversions the problem is the factory loom, which was sized for a halogen bulb and now has to carry the inrush current of a bi-xenon ballast through thin wire and a tired switch.\u003c\/p\u003e\n\u003cp\u003eThis harness pair moves that load where it belongs. The relay takes the switching current directly from the battery, so the original wiring only carries the signal rather than the full draw. Bulbs reach full brightness in a single step, the high and low beam change is crisp, and the load on the factory headlight switch drops far enough to end the dimming that shows up when the lights are switched on at idle.\u003c\/p\u003e\n\u003cp\u003eEvery connection is plug and play for H4 and 9003 sockets, which means no cutting into the factory loom and no soldering. The pair covers both sides of the vehicle, so the installation is symmetrical rather than a single-side experiment.\u003c\/p\u003e\n\u003cp\u003eFor workshops, the value is in diagnosis. When a customer complains of flickering bi-xenon lights, a relay harness is the cheapest first test, and having a pair on the shelf avoids waiting on a delivery before the car leaves the bay.\u003c\/p\u003e\n\u003cp\u003e\u003cem\u003eGive the current a shorter path. The light follows.\u003c\/em\u003e\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-features\" style=\"margin-top:26px;\"\u003e\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul style=\"padding-left:18px;\"\u003e\n\u003cli style=\"margin-bottom:8px;\"\u003e✦ Relay harness pair that takes switching current directly from the battery\u003c\/li\u003e\n\u003cli style=\"margin-bottom:8px;\"\u003e✦ Reduces load on the factory headlight switch, ending dimming and flicker at idle\u003c\/li\u003e\n\u003cli style=\"margin-bottom:8px;\"\u003e✦ Plug and play for H4 and 9003 sockets with no cutting or soldering\u003c\/li\u003e\n\u003cli style=\"margin-bottom:8px;\"\u003e✦ 12V rated for 35W and 55W bi-xenon and HID bulb conversions\u003c\/li\u003e\n\u003cli style=\"margin-bottom:8px;\"\u003e✦ Two harnesses per pack, covering both sides of the vehicle\u003c\/li\u003e\n\u003cli style=\"margin-bottom:8px;\"\u003e✦ Direct replacement design that leaves the factory loom intact\u003c\/li\u003e\n\u003cli style=\"margin-bottom:8px;\"\u003e✦ Rated for bi-xenon, HID and high-output halogen upgrades\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-specs\" style=\"margin-top:26px;\"\u003e\n\u003ch3\u003eTechnical Specifications\u003c\/h3\u003e\n\u003cul style=\"list-style:none;padding:0;\"\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eVoltage:\u003c\/strong\u003e 12V DC\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eApplication:\u003c\/strong\u003e H4 and 9003 bi-xenon, HID and halogen upgrades\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eBulb Rating:\u003c\/strong\u003e 35W and 55W compatible\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eContents:\u003c\/strong\u003e 2 x H4 controller harness, one per side\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eInstallation:\u003c\/strong\u003e Plug and play, direct replacement\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eColour:\u003c\/strong\u003e Black cable with standard connectors\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eSwitching:\u003c\/strong\u003e Relay-driven, draws power from the battery\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eCompatibility:\u003c\/strong\u003e Fits vehicles using H4 or 9003 headlight sockets\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eSoldering Required:\u003c\/strong\u003e None\u003c\/li\u003e\n\u003cli style=\"padding:9px 0;border-bottom:1px solid #eee;\"\u003e\n\u003cstrong\u003eBest For:\u003c\/strong\u003e Headlight upgrades, flicker diagnosis, workshop stock\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-applications\" style=\"margin-top:26px;\"\u003e\n\u003ch3\u003eWhere It Fits\u003c\/h3\u003e\n\u003cp\u003eThis suits anyone converting a halogen headlight to bi-xenon or HID and finding the result inconsistent. It also fits the simpler case of an older vehicle whose headlights dim noticeably when the switch is pressed, a symptom that usually points at the factory loom rather than the alternator. Auto electricians keep a pair as a diagnostic part, and detailers and restorers use the harness to keep a classic vehicle's original wiring untouched during a lighting upgrade.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-compare\" style=\"margin-top:26px;\"\u003e\n\u003ch3\u003eHow It Compares\u003c\/h3\u003e\n\u003ctable style=\"width:100%;border-collapse:collapse;font-size:14px;color:#2d2d2d;\"\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth style=\"background-color:#1a1a2e;color:#ffffff;padding:10px 14px;text-align:left;\"\u003eConsideration\u003c\/th\u003e\n\u003cth style=\"background-color:#1a1a2e;color:#ffffff;padding:10px 14px;text-align:left;\"\u003eThis Item\u003c\/th\u003e\n\u003cth style=\"background-color:#1a1a2e;color:#ffffff;padding:10px 14px;text-align:left;\"\u003eOrdinary Alternatives\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr style=\"background-color:#ffffff;\"\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eCurrent path\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eBattery feed through a relay\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eFull load through factory switch and thin wire\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color:#f9f9f9;\"\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eBrightness stability\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eFull output immediately on switch\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eDim start and flicker at idle\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color:#ffffff;\"\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eInstallation\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003ePlug and play, no cutting\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eSplicing into the factory loom\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color:#f9f9f9;\"\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eContents\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eTwo harnesses, both sides covered\u003c\/td\u003e\n\u003ctd style=\"padding:9px 14px;border-bottom:1px solid #e8e8e8;\"\u003eSingle harness, second side purchased separately\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-note\"\u003e\n\u003ch3\u003eWhy It Matters\u003c\/h3\u003e\n\u003cp\u003eThe reason a relay harness solves so many lighting complaints is electrical, not cosmetic. Thin factory wire adds resistance, and resistance turns current into heat and voltage drop. Feeding the bulb from a short battery path removes most of that drop, so the bulb sees the voltage it was designed for and the switch stops carrying current it was never rated for.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-faq\" style=\"margin-top:26px;\"\u003e\n\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\n\u003cdiv style=\"margin-bottom:15px;\"\u003e\n\u003cp style=\"margin:0 0 4px 0;\"\u003e\u003cstrong\u003eQ: Will this work with LED bulbs as well as HID?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp style=\"margin:0;\"\u003eA: Yes. The harness carries the load for any H4 or 9003 bulb drawing up to the rated wattage, including high-output LED conversions.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"margin-bottom:15px;\"\u003e\n\u003cp style=\"margin:0 0 4px 0;\"\u003e\u003cstrong\u003eQ: Does the relay make an audible click?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp style=\"margin:0;\"\u003eA: A standard relay click is normal and confirms the switching circuit is engaging correctly.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"margin-bottom:15px;\"\u003e\n\u003cp style=\"margin:0 0 4px 0;\"\u003e\u003cstrong\u003eQ: Is there a fuse in the harness?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp style=\"margin:0;\"\u003eA: The harness takes its feed directly from the battery and is designed to work with your existing fuse protection. Check your vehicle wiring before installation.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"margin-bottom:15px;\"\u003e\n\u003cp style=\"margin:0 0 4px 0;\"\u003e\u003cstrong\u003eQ: Do I need to disconnect the battery?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp style=\"margin:0;\"\u003eA: Yes, disconnect the negative terminal before fitting any electrical part. Installation itself is plug and play at the headlight connector.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"margin-bottom:15px;\"\u003e\n\u003cp style=\"margin:0 0 4px 0;\"\u003e\u003cstrong\u003eQ: Does this suit a 24V truck?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp style=\"margin:0;\"\u003eA: It is rated for 12V systems. Confirm your vehicle voltage before ordering.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-faq-more\" style=\"margin-top:26px;\"\u003e\n\u003ch3\u003eMore Questions From Buyers\u003c\/h3\u003e\n\u003cdiv style=\"margin-bottom:15px;\"\u003e\n\u003cp style=\"margin:0 0 4px 0;\"\u003e\u003cstrong\u003eQ: Do I need to remove the bumper to fit these?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp style=\"margin:0;\"\u003eA: No. The harness connects between the factory plug and the bulb, so installation happens at the headlight housing rather than behind the bumper.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"margin-bottom:15px;\"\u003e\n\u003cp style=\"margin:0 0 4px 0;\"\u003e\u003cstrong\u003eQ: Will this fix a flickering bi-xenon light?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp style=\"margin:0;\"\u003eA: It resolves the most common cause, which is voltage drop through the factory loom. If flicker continues afterwards, the ballast is the next item to test.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-gallery\" style=\"margin-top:30px;text-align:center;\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0503\/6412\/1244\/files\/H99cb8c87f14549f196b49b58e7dd86b34.webp?v=1729897556\" alt=\"\" style=\"max-width:100%;height:auto;border-radius:6px;margin:6px 0;\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0503\/6412\/1244\/files\/Hbdd3f457fe18427b846592466d076752v.webp?v=1729897556\" alt=\"\" style=\"max-width:100%;height:auto;border-radius:6px;margin:6px 0;\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0503\/6412\/1244\/files\/Hed054fdef4164040b7e82b4d310a6a09O.webp?v=1729897556\" alt=\"\" style=\"max-width:100%;height:auto;border-radius:6px;margin:6px 0;\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0503\/6412\/1244\/files\/Hd424de0632884c2b8abe4905a559d7c2v.webp?v=1729897556\" alt=\"\" style=\"max-width:100%;height:auto;border-radius:6px;margin:6px 0;\"\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"product-promise\" style=\"margin-top:28px;padding:18px 20px;border-left:3px solid #0a66c2;background:#f6f8fb;\"\u003e\n\u003ch3 style=\"margin:0 0 10px 0;font-size:17px;\"\u003eThe EastSupplier Promise\u003c\/h3\u003e\n\u003cp style=\"margin:0;\"\u003eEvery unit is inspected before it leaves the warehouse, packed for international transit, and backed by a responsive support team. If a shipment arrives damaged or does not match the specification below, we replace it. Sourcing at scale should not require guesswork.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cscript type=\"application\/ld+json\"\u003e\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"Product\",\"name\":\"The Relay Loom | H4 Bi-Xenon Headlight Wiring Harness Pair\",\"description\":\"The Relay Loom | H4 Bi-Xenon Headlight Wiring Harness Pair\",\"sku\":\"ES-H4-RELAY\",\"brand\":{\"@type\":\"Brand\",\"name\":\"EastSupplier\"},\"offers\":{\"@type\":\"Offer\",\"url\":\"https:\/\/eastsupplier.com\/products\/the-relay-loom-h4-bi-xenon-headlight-wiring-harness-pair\",\"priceCurrency\":\"USD\",\"price\":\"16.01\",\"availability\":\"https:\/\/schema.org\/InStock\",\"itemCondition\":\"https:\/\/schema.org\/NewCondition\"},\"aggregateRating\":{\"@type\":\"AggregateRating\",\"ratingValue\":\"4.7\",\"reviewCount\":\"18\"}}\n\u003c\/script\u003e","brand":"East Supplier Platform","offers":[{"title":"Default Title","offer_id":46413367509215,"sku":"1005003119963816-Default Title","price":16.01,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0503\/6412\/1244\/files\/H99cb8c87f14549f196b49b58e7dd86b34.webp?v=1729897556","url":"https:\/\/eastsupplier.com\/pt-it\/products\/the-relay-loom-h4-bi-xenon-headlight-wiring-harness-pair","provider":"EastSupplier Platform","version":"1.0","type":"link"}