I bought the car for my daughter a few months ago. The dash lights were dim at best, but now are completely out. I have ruled out individual bulbs since they are all out at the same time. I pulled the switch and tested the resistance. The value remains constant throughout the dial range. That isn't right. I figured I could bypass the switch and just go full bright all the time, but whenI checked the 3 wire plug, I found the center wire is ground and the two red wires on left and right are hot at 12+ volts. It seems to me that one would be hot when the lights are on and the other hotonly when the lights are on, the switch is connected and adjusted to let some voltage through to illuminate the dash lights to the desired level. Any idea why they are both hot with the lights on and no switchplugged in?[>:]

 

The circuit diagram (picture 1) indicates that the left and right wires should indeed be hot.

Picture 2 details additional tests that may help you.

 

RonJ, Following the diagram it would appear that the red/blk is always hot but the red is only hot after passing through the resistor since they are not connected in any way, nor does the diagram indicate a power source to the red wire. Isn't that what you see?

 

Ok, I just checked the plug. Blk gives .001 ohms to ground so I'm good there. Red is at 12+ volts and red/blk is at 12+ volts. The funny thing is I did a continuity check between red and red/blk and came up with .002 ohms. Something isn't right. There shouldn't be any continuity because that would completely negate the switch in the system. I need a hammer...

 

Test 3 in picture 2 indicates that the red wire is indeed hot. The directions of the large open arrowheads in the circuit diagram (picture 1) confirm this idea.

 

The circuit diagram also indicates that there should be continuity between the red and red/black terminals. The test bypasses the switch. Your measurements at the 3P connector seem fine. Replace the dimmer switch.

By the way, did you complete the tests described in picture 2? The results should confirm the need to replace the dimmer switch.

 

You're right, the switch needs to be replaced. I still don't quite understand the flow, but that is a moot point. I appreciate your help. I will save the diagram and tests for future reference.

 

By the way, Test 3 in Picture 2 also shows you how to have full bright all the time, if this is what you want.

 

It's not a simple reostat. The module pulses the red wire to ground to control the brightness. If you want high brightness it sends long pulses with near 100% on time. To dim the lights it sends pulses with shorter on time, so the average voltage at the bulbs is less than 12 volts.

 

Are you saying that the way the controller works precludes its testing by simple resistance measurements? If so, then this would explain why the service manual does not suggest any direct testing of the controller and why a bad switch instead must be inferred by failing to find problems in the Controller Input Test.