Product details
Maypole 12V 7-way bypass relay with audible buzzer – trailer and caravan electrics
This Maypole bypass relay is a simple, no-nonsense way to run trailer and caravan lights without loading up your vehicle’s lighting circuits. It sits at the rear light wiring, drives the trailer lamps directly and listens in on the indicator circuits with a built-in buzzer so you’ll know if a trailer bulb has popped.
what it does
The unit picks up and reproduces the vehicle’s rear light signals for indicators, tail, brake and fog lights — including vehicles that use shared tail/brake or tail/fog circuits. The audible monitor alerts you to indicator or flasher faults and mutes automatically when the hazard warning lights are used. There’s also an ancillary output if you want a dash warning lamp or a second buzzer.
key features and benefits
- Works with most vehicles and suits both filament and LED rear lamps, so no need to faff about swapping bulbs.
- Doesn’t add load to the vehicle lighting circuits, preserving sensitive vehicle electronics and avoiding phantom warnings.
- Built-in buzzer keeps an ear on the indicator/flasher circuits, giving an unmistakable alert if a trailer lamp fails.
- Can tell the difference on dual-voltage tail/brake and tail/fog setups used in shared rear clusters.
- 55 cm cable length allows a neat installation at the rear light clusters without excess, messy wiring.
- Ancillary flasher/indicator monitor output gives the option of a dash lamp or an extra buzzer if desired.
compatibility and fitment
It’s compatible with many vehicles, but there are limits. The relay will only work with multiplexed or shared-signal systems if the necessary signals are present as physical wires at the rear lamp clusters — it needs separate indicator signal wires to each rear cluster. It won’t work on fully digital or network-only lighting systems (for example, CANbus setups where no direct rear signal wiring exists). If you’re not sure, get a qualified auto-electrician or a towbar fitting centre to check your wiring before buying.
technical details
Manufacturer: Maypole — Part number MP3877. Cable length: 55 cm. Item weight: approx. 140 g. Product dimensions: 18 x 15.8 x 3 cm. Colour: black. Material: brass contacts. Power: 12V, nominal wattage 16.4W. Mounting: screw mount. CE marked. Made in the UK.
Typical uses: towing a trailer or caravan for holidays and DIY runs, offering a reliable, low‑maintenance way to monitor indicators and avoid dashboard warnings on vehicles with direct rear wiring. Problems solved: no more confusing flicker or dimming from shared circuits, clear audible warning of a blown trailer indicator, and a tidy installation that won’t put extra strain on your vehicle’s lights.
Fitment note: professional installation is recommended. A competent auto-electrician or towbar fitment centre can confirm whether your vehicle’s wiring is suitable and ensure a clean, safe install. If your car uses fully networked lighting without individual rear wiring, this relay will not function correctly.