September 25, 2019

TT #113 Hints on Replacing RV Light Fixtures & Bulbs

By: Rob Lowe

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In this Technical Tip, I will address some of the questions that are posed when people call us looking for a lighting solution for their RV. In the next one I will address where to find common parts used on older RVs which are not available from the original RV maker for various reasons. While the focus will be on older RVs, the concepts apply to newer ones as well.


Replacing Exterior Light Fixtures with L.E.D. Units:

I receive many inquiries from older motorhome owners, that are looking for a parts source for exterior marker or taillight fixtures. Often the ones on their coach are damaged, or ‘milky’ in appearance, having oxidized or deteriorated over the many years since the coach was manufactured. Usually the caller relates the fact that they have contacted the RV maker (i.e. Fleetwood) or the new company, (REV Group), which makes the same RV brand as theirs, only to learn that the parts department does not have the original light fixtures. Usually, this is due to the fixture having been discontinued, although in some cases, their coach is so old, that parts are no longer stocked. What can they do?

A recent caller was seeking some oblong red and amber side marker lights that were about 4 inches (10 cm) long and about 1.5 inches (3.8cm) wide with rounded ends that have been discontinued. In our discussion, the owner mentioned that the original light maker (Bargmann) no longer makes or sells the fixture. There is a L.E.D. replacement in either red or amber that appears to be a newer version of the original lamp. The question is: "Can I install this replacement without creating additional issues?” My answer is ‘Yes!’

Typical Marker Light Fixture

The original light fixture will have a removable red or amber lens cover that allows replacement of the bulb. There is a slot on one end between the light mounting base and the red or amber lens cover, that a large coin or wide flat screwdriver can be inserted into, allowing the cover to be pried up and removed, thereby exposing the incandescent light bulb and the fixture mounting screws. The L.E.D. replacement often has the lighting components sealed into the colored lens, with the base to be attached to the RV sidewall with screws, then the light assembly is snapped onto the base. If one does not know the brand of the original marker lights, often a Google search for "RV Marker lights” will bring up potential sources. Occasionally searching for the numbers molded on the lens will reveal the original equipment maker. Once a suitable replacement has been located, the RVer can determine whether to use an incandescent bulb fixture as the original or a L.E.D. replacement.

LED Replacement Marker Light Fixture


Replacing the light assembly involves removing the original and connecting the two existing RV wires to the wiring on the new fixture. The wire colors (often black and white) may match those of the light removed however the polarity of those wires may be reversed from those of the original. On an incandescent bulb replacement, the wiring connections are not critical, matching what is there should be fine. Since L.E.D. lighting will only function if the wiring is correctly connected and the lamp will not be harmed if connected improperly, the following method of testing is a quick way to determine the proper wiring connections. Remove the existing light fixture from the body side and then enough of the original wiring to reveal the butt connectors that made the connection from the RV wiring to the original light fixture. If the wiring is long enough, cut the wires at the butt connectors, bare about 3/8 inch (1 cm) of each wire end and temporarily connect the two wires to the new fixture. Turn on the motorhome’s parking lights and determine if the light operates. If not, simply reverse the wires. Do not allow the two wires to touch each other with the power turned on, since if they do, there will be a short circuit which will blow the fuse. Once the correct polarity is determined, turn off the power and install new butt connectors to permanently connect the RV wiring to the fixture. Note that it is not unusual for the wiring from the RV to be opposite to the light fixture. (i.e. a white wire from the RV connected to the black on the fixture and black wire from the RV connected to the white on the lamp assembly). This discrepancy arises from either wire conventions changing in the intervening years or attempts by the light manufacturer to standardize their assembly protocols across their product line. This may be different from the original. Mount the new fixture using new screws, after sealing the original mounting holes in the body with caulking. Use the plastic gasket (if supplied) on the new lighting fixture, then lightly caulk around the newly installed fixture to seal it to the RV body.    


As I mentioned in previous Technical Tips (TT) that address changing light fixtures (TT #85 & #91), conversion to L.E.D. external lights should always involve replacement of the complete fixture over a simple bulb exchange. This is because L.E.D. light output factors do not match the original incandescent bulb. Installing a L.E.D. bulb in a fixture designed for an incandescent bulb, will likely compromise safety. In addition, the low power consumption characteristics of L.E.D. replacement bulbs may prevent operation, given the corrosion that naturally occurs on non-sealed conventional light fixtures, thereby compromising the safe operation of the brake, turn signal and taillight/marker lighting.

For taillight replacement, the original maker may no longer be in business and the accessory market may have similar fixtures which will fit the original location on the RV. (See Technical Tip #85 for more detail).

After replacement of the light fixtures, I recommend regular applications of a UV blocking protectant such as 303 Protectant or similar. This will slow down the deterioration of the plastic lens and reduce the oxidation that leads to a milky lens.


Replacing L.E.D. Bulbs in Interior Light Fixtures:

Another frequent question relates to installation of a replacement L.E.D. bulb into a ceiling or cargo bay light fixture that has an opaque white or clear plastic lens covering the bulb. The typical replacement bulb will have either a bayonet or wedge base, as shown in the photos. Typical LED Replacement BulbsWhen these replacements are placed into the fixture, most will light when turned on. Occasionally one does not; the natural assumption is that the replacement L.E.D. is defective. However, when installed in another fixture the light operates. Remember that L.E.D. bulbs are one-way streets for electricity. They give off light only if the electricity flows in the correct direction. On the bayonet (silver base) bulbs, the design is that the positive terminal (often referred to as the ‘Hot’ one) is the center pin on the base and the silver side is ground. When assembling the RV with the original incandescent bulbs, the electricity will flow in either direction. If a fixture is improperly connected to the RV wiring, all lights will operate. However, installing a L.E.D. bulb makes the correct polarity, critical to proper lighting. The solution on this type of light fixture is to remove it from the ceiling or cargo bay and reverse the wiring. Then, the L.E.D light will operate. With a push in wedge bulb, flipping the bulb over 180 degrees, effectively reverses the wiring and the light will function. Rarely is the bulb defective, the wiring usually is reversed. We often assume the installer made a careless installation error however each light maker has differing protocols for the color of the positive 12 Volt (‘hot’) and ground wires. Sometimes it is the black wire, on other fixtures it can be the white wire. Variations can occur between fixture styles. The patio door exterior light may be reversed from that of the interior light fixtures. The wall sconces can vary as well. It is difficult on an assembly line to know the variations and errors inadvertently occur that are irrelevant when an incandescent light bulb is installed. Conversely, the wiring and electricity flow is critical when L.E.D. bulbs are installed in the same fixtures.  It is not unusual to have to reverse the wiring connections on some fixtures to achieve operation of all replacement bulbs. The color of the wire insulation does not definitively determine whether the wire is a ground or one carrying positive 12 volts.


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