I call this an advanced question because this one really has me stumped and will likely require your very best thinking cap also if you choose to try your skill at solving the puzzle. Only read further if you like a challenge.
The outside front light
(over the propane
tank and battery) on my Sept 2015 vintage Scamp
was working fine last fall
. On the off season, I installed a TriMetric meter and companion solar
charger with a connection to a receptacle. All of this was put in the compartment under the front sofa (door side). While load testing the solar
charger by turning on every 12 volt item at once (and while off shore power), I discovered that the front outside light
would not come on.
It is certainly possible that I pulled a connector loose or something while installing the meter and solar
wiring, so I started with standard troubleshooting steps.
Removed bulb and noticed that since Scamp
uses such cheap light
fixtures the bulb socket was a little corroded after only six months of being outdoors. Cleaned it all up well, still no light.
Checked the bulb visually and for continuity. It checked out as good.
Substituted a LED bulb and there was light. Operation was normal with the LED bulb
Tried another incandescent bulb with same results as the first bulb, no light.
Hooked up both incandescent bulbs to a 12 volt supply with alligator clips and they both lit up fine. The bulbs are good
I can actually see the center pin make contact when I put the bulbs in. Everything sure seems to be making good contact.
Measured the voltage at the blub socket (with the switch on) and read 12.7 VDC at the center positive contact and the part of the socket where the bulb base and tab make contact.
Scratched head since that seemed to be the next appropriate step.
At this point in my story I might offer kudos to those of you who 1: noticed that the LED bulb with low current draw worked fine but the higher amperage incandescent did not, and then, 2: concluded that maybe there is a bad connection that is allowing enough power to get the 12.7 VDC reading but is not good enough to pass the amount of current which the incandescent needs. If that were the case I would expect the voltage to drop under the heavier load, so next step…
I removed the wire nut off the positive wires, made sure they were well twisted together, and hooked up the multimeter positive lead to the positive wires. With the incandescent bulb in and the switch on, I read the voltage with the negative meter lead on the outside of the socket, and then on the base of the bulb. Voltage was constant when the switch was on - there was no voltage drop
. At this point there was only one more test I could think of and it was just a little risky.
With extreme care as to not cause a short, I removed both wire nuts in the light fixture to expose the positive and negative feed wires and touched them to the incandescent bulb, which I almost dropped when there was a small spark and the bulb lit up! So we know the wiring to the fixture is OK
That means the fixture seems to be the issue. It worked fine with an incandescent bulb a few months ago but no longer does. It does work with LED bulbs however which are equivalent with the same base. Explain that!