Overview

The Attwood Marine 14133-6 is a trailer light circuit tester used to check common lighting circuits before you start pulling apart a harness or replacing lamps. It plugs into the wiring harness and uses indicator lights to show where the fault is, helping you sort out taillight, ground, and left or right turn-signal issues.

Its 4.75 x 3.5 x 0.5 inch size makes it easy to keep in the tow vehicle, glove box, or trailer tool bag. For boat trailers, it gives you a quick way to check the lighting side before a ramp run, after rewiring, or when an intermittent light fault starts showing up on the road.

Key features

• Inline circuit tester for trailer light wiring checks
• Indicator lights help identify faults in taillight, ground, and left or right turn-signal circuits
• Compact 4.75 x 3.5 x 0.5 inch form factor that stores easily with trailer spares and tools
• Useful for troubleshooting before towing, after connector service, or when one side of the trailer lights stops working

Compatibility and fit

This tester is meant for trailer lighting diagnostics, not as a replacement harness, adapter, or light assembly. The main fit point is the connector style on the trailer wiring, so it is worth checking your trailer plug and tow-vehicle socket before ordering.

On a boat trailer, this kind of tester is helpful when you want to narrow the problem down before replacing bulbs, cleaning grounds, or opening up the harness. That can save time when the trailer has been exposed to repeated launch and retrieval cycles and the issue may be in the wiring rather than the lamp itself.

Use and troubleshooting

Setup is straightforward: connect the tester to the trailer lighting wiring, then read the indicator response for the circuit you are checking. It is a practical tool for seasonal trailer prep, post-repair checks, and pre-trip inspections when you want to confirm the lighting system is working before heading to the ramp or back home.

This is a good match for boat owners who trailer regularly and want a simple way to isolate common light-circuit faults without carrying a larger electrical test kit. It also fits well in a small onboard locker or tow-rig tool bag where space is limited.