OK so I did some more testing. Inc=Incandescent; N/A=No Bulb; LED = LED Bulb. On/Off indicates the state of the switch as either on or off. Asterisk * indicates if bulb is lit. Here is what I did:
Test with Incandescent bulb on Drivers Side.
Code:
Driver Side Passenger Side
Inc-On 12.1v* N/A-Off 4.0v
Inc-On 12.0v* N/A-On 12.0v
Inc-Off 0.0v N/A-Off 0.0v
Inc-Off 0.0v N/A-On 1.3v
Inc-On 12.1v* LED-Off 4.0v
Inc-On 12.0v* LED-On 12.0v*
Inc-Off 0.0v LED-Off 0.0v
Inc-Off 0.0v LED-On 1.3v
The last test above shows that the LED bulb turns off if the incandescent bulb is turned off.
For this round I moved the incandescent bulb to the passenger side and repeated the tests.
Code:
N/A-Off 4.0v Inc-On 12.0v*
N/A-On 12.1v Inc-On 12.0v*
N/A-Off 0.0v Inc-Off 0.0v
N/A-On 7.7v Inc-Off 0.0v
LED-Off 4.0v Inc-On 11.9v*
LED-On 12.1v* Inc-On 11.9v*
LED-Off 0.0v Inc-Off 0.0v
LED-On 7.8v Inc-Off 0.0v
Last round of testing with two LED bulbs.
Code:
LED-On 4.5v LED-Off 1.1v
LED-On 4.5v LED-On 4.5v
LED-Off 1.1v LED-Off 1.2v
LED-Off 0.2v LED-On 4.5v
None of the LED's turned on. An interesting but confusing find was I did notice that if I bridged a positive and negative terminal, didn't matter which positive or negative,
with the incandecent bulb, that all three lights would illuminate (provided the switches were on). Bridging positive/negative of the same terminal or positive of one and negative of the other, would yield the same results. I thought maybe I found a fix, just bridge them with a wire permanently, so I attempted a test to measure the voltage when the switches were
off to see if it was viable fix but the LED would flicker and go out.
Improbable. A series circuit would usually drop even more voltage at the higher current of the original incandescent lamps.
Although there are circuts that require a minimum amount of current to flow I think it is unlikely that this is the case here.
- Did you measure the voltage across the LEDs at the time they are supposed to be on?
- Are there any other lights that do not come on when the LEDs are installed in the map lamp fixture but that do come on with incandescent lamps installed?
- Another check you could do: Instal an incandescent lamp into one of the sockets, this makes the setup work per your description. Then connect the LED lamp in parallel to th eincandescent one using some wire for the eletrical connection. Does the LED lamp light now? This would indicate that, contrary to my above assumption, a certain minimum current is required.
I haven't noticed any other lights that do not come on. The only other interior light is the dome (with LED bulb), which functions correctly regardless of other factors.
For the second suggestion, I thought that the wiring harness illustrated in my first post shows it's parallel. If it is, then the LED does turn on, so long as the incandescent switch is switched to on.