QuestionThe front and rear marker lights on my 2008 dodge ram 1500 will not shut off. They are on slightly dimmed. I assume it is a short. But not sure where to start.
AnswerHi Jeremy,
My review of the wiring suggests that the side marker lamps are in parallel with all the other parking lamp filaments and basically should all be misbehaving in the same manner if the issue has to do with some 'short' current flowing into the circuits. Furthermore, the left and right side circuits parking lamp circuits are powered from separate fuses, so I don't see how both sides could be similarly affected were this a short of some sort.
As I read the manual, the marker and parking lamps are controlled by the totally intergrated power module (in the engine compartment), the instrument cluster, and head lamp switch.
These communicate information digitally to one another. Commands can be issued to turn on or turn off the parking lights in case of certain problems recognized. So I suspect that is why the markers are staying on.
Probably the best way to diagnose this issue would be to get a fault code readout of the digital communication system using a diagnostic readout box. A nationwide autuparts store such as Autozone, will often do that for free. If not an independent shop will often do it for around $40. If you can get a fault code number let me know as I have the manual that says what these mean and what to do about them.
It is interesting that although the park and marker lamps should misbehave identically being electrically in parallel, the bulbs are of different types so that at a given sub-optimal voltage the markers could be 'on' while the parking bulbs are 'off', visually.
Another possibility is that the parking lamp position of the headlamp switch is 'off-value'.
That switch, rather than being hardwired, instead has a specific range of output resistance (and therefor output voltage that is interpreted by the power module) to provide voltage or not to the parkiong lamp pair of circuits. You could remove the parking lamp switch (remove cluster bezel) and measure the resistance in ohms between pins 1 and 3 of that switch's socket when you have it set for parking lamps to be 'on'. Let me know that ohm reading, and also what is the ohm reading when the switch is in the 'off' position. It should be infinite ohm when 'off' and around 1000 to 1200 ohms when set for 'park'. It is the case that the type of bulb used for the marker is different from the type of bulb used for park and that is why one will emit light while the other won't when there is a wrong voltage on the parking lamp circuit.
Please let me know how this works out.
Please 'rate' my answer (see PS below). I would appreciate a nominaton for 'volunteer of the month' at Allexperts is you believe that I deserve that.
Thanks,
Roland
