LED Marker & Clearance Lights for Trucks and Trailers

Diameter and grommet, in that order

A marker lamp is specified by the diameter of the lamp body, and the grommet is what makes it seal and hold. The most common small size is 3/4 inch, which is the little bullet lamp you see dotted along a trailer skirt; larger round markers run around 2 inches. If the old lamp pulls out and leaves the rubber behind, take the measurement off the grommet bore, because that is the hole the new lamp has to fill.

Buy the grommet with the lamp unless you are certain the old one is still soft. A hardened grommet is why a replacement lamp leaks and fails again in a season, and it costs a fraction of the lamp.

Red or amber, and where each goes

The colour rule is simple and it is not negotiable at an inspection: amber faces forward and to the sides ahead of the rear, red faces rearward. On a long trailer the intermediate side markers are amber up front and red at the back, with the change happening around the midpoint.

If you are replacing one lamp, match what came out and you will be right. If a previous owner has been creative with colours, work from the placement rules rather than from the trailer as you found it.

Why they get replaced in handfuls

A trailer carries a lot of marker lamps and they live in the worst place on the vehicle: low, exposed to spray, salt and stone chips, and vibrated constantly. They do not fail one at a time so much as they begin failing, and the first one out is a signal about the rest.

That is why the sensible purchase is several. A handful of lamps and a handful of grommets in the truck turns a roadside marker failure from a delay into a five-minute stop.

LED Marker & Clearance Lights for Trucks and Trailers — FAQ