Trunk/Cargo Lamp Issue (Socket Voltage Changes with Bulbs?)

[shsolus]

I changed all my interior and license plate bulbs to CorkSports' LED ones several months ago.

Recently I noticed is that the cargo lamp stays on all the time, regardless the hatch position. When I put the OEM regular bulb back, it does not work at all.

So I used my multimeter and here are what I found:

The voltage across the socket changes with bulb installations:

• If no bulb is installed: 11V when hatch open, 0.1V when hatch closed.
• When regular OEM bulb is installed: Almost 0V when hatch open, almost 0V when hatch closed. The bulb does not light in either case.
• When LED bulb is installed: About 5V when hatch open, about 5V when hatch closed. The bulb lights in both cases.

So pretty confused, from the open (no bulb) test it seems that the voltage is just fine, maybe there is a very large resistance on the way so the voltage for the bulb becomes low? But then why does the LED bulb still have 5V?

Any thoughts? Thank you.

(eek2)(eek2)

 

[mongo2004]

Ok let me see if I can explain. Unlike the dome lights which are controlled by a relay with a hard contact, the cargo light is controlled by a solid state output(possibly a darlington transistor) located in what I believe it is called the RCM. The solid state output sounds like it has failed. The reason why I say this is because when the fail they no longer switch and they leak current. So what is happening is that when you put the bulb in it is using all of the leakage current (driving the voltage to zero) but not enough current to be able to turn the light on. When you put the led in it is a much higher impedance device whith also the capability of turning on the light at a much lower voltage level <5v. The leakage current is turning on the led. Sounds like you need to replace the RCM.