Monday, January 17, 2011

License Plate Lights

Problem: License plate lights do not work

Discussion:

The license plate is mounted in a recessed area on the rear of the coach. The two license plate lights are located in the upper 'ceiling' of the recess. The configuration of the lights is two-piece. That is, each light has a bulb socket recessed in the 'ceiling' and a separate lens and lens holder which 'pushes' into the recess and is retained by friction of its triangular shaped tangs inside the hole that contains the bulb socket. Picture clear? O.K., here's the problem:

Water that runs down the rear of the LD runs in some small part into the license plate recess, following the smooth contours of the aft coach wall. Some of that liquid runs into the lens / lens holder, which forms a neat little cup to hold the liquid. The lens holder shouldn't rust, right? Believe me, it rusts on the inside! After a few months, some of that corrosion crawls up into the bulb socket, which corrodes, as does the light bulb base ane the electrical contacts for the bulb. First one, then the other of the license plate lights are likely to quit working because of that corrosion.

Replacing the bulb:

You probably have this type of light:

<http://www.ptrailerusa.com/products/License-Plate-Light-%252d-Chrome-%252d-PM438.html >

If so...they are a bear to change because LD seals them with polyurethane to water-proof the hole. The assembly normally would go in as one piece but since it is glued, usually just the cap pops off.

Using a small screwdriver, pry the cap off, working your way around the cap as you go. It is difficult because you are breaking a glue bond between the cap and base. Before starting, you might want to lay down a few layers of masking tape, around the cap, to prevent chipping of the gel coat.

After the cap is off, the fun begins. You need to cut out the polyurethane that remains, in both the cap and the base, before replacing the cap... Exacto knife time.
The bulb is a #67. Butter the bulb's base with a good layer of dielectric grease before inserting. This helps keep the contacts clean.
Keep working on removing the old poly until the cap will go on.
Add a little new polyurethane to seal it and to keep the cap from unintentionally popping off. If necessary, tape in in place until the poly cures.

If the license plate light base was not glued in, you can simply replace the entire assembly, being inexpensive. LD's attention to sealing is great but this makes the simple job of replacing a bulb, which has a limited lifetime, into a much bigger project.

Be careful and go slow. If the assembly becomes damage, new ones are available at most any good RV store. Just tape the hole up until you get a new one installed.
Wonder if LD left enough extra wire so a new bulb assembly can be installed?

Repair:

Removal of the license plate lens and lens holders required use of adjustable pliers, with the lens cover protected by some cloth. I used a piece of synthetic chamois, which worked well. I had to rotate the lens covers back and forth a few times while pressing down to get it loose. When removed, both were a mass of rust inside. Removal of the bulbs revealed their bases and the bulb sockets were also corroded. Electrical grease had been applied by the Mother ship when our LD was built but it did not sufficiently protect the bulb base or socket from corroding. I cleaned things up with a wire brush and a knife, applied some more electrical grease and reassembled everything. Both bulbs worked.

Suggestion:

Replace these recessed bulb assemblies with a marine (boat trailer) license plate light, which is designed for immersion in salt water. Fish the license plate light wires out of the existing recessed holes, tape off one set and stowed back inside the coach body and run the other to the new light assembly. Seal both of the old openings with PR 255. Mount the new light bracket with sealed screws to the 'ceiling' of the license plate recess; the main part of the light assembly will be outside the recess.

Tip:

Don't only check your lights before each trip, check them a few days before so you'll have time to fix any unforeseen problems before you drive off.

Contributor: Don McGlothen, Larry Wade

Revised 18 Aug 11

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