That is correct. I hope to find a source for the bulbs so I can de-solder the pins to disassemble the switch and replace the bulb. I'm seriously hoping this fixes the problem. No Ohms between pins H and G on the switch has to mean the bulb is bad, correct?

 

Cracks in the solder joints never crossed my mind until I saw your post but it got me thinking this might be what was causing my 4HI indicator to not always light up. Quick and easy fix. Now I have an OEM spare. Thanks for the write up.

 

The first step is always verify power and ground. The rest of the control logic uses that ground on black and that all works so its most likely either a power problem or a problem internal to the module so first check voltage between the gray illumination power wire and the black ground wire on the harness with the module unplugged. and if thats good then whats the resistance between those two connector sockets on gray and black on the module with the module unplugged?

George

 

I tested the gray wire to the black on the blue connector and got 10vdc. I rotated the dimmer switch up and down and the voltage changed from 10vdc down to 6 and back up so I'm assuming this is means the connections are good and should be enough to power the illumination lamp in the switch.

I tested pins G(gray wire) and H(black wire) on the switch module with a new meter and got nothing. No Ohms. Bad bulb?

 

Do you mean zero ohms or an open circuit/infinite ohms, usually displays 0L?


George

 

Sorry, OL no continuity. Open circuit. I believe the circuit should have around 10-30ohms if the bulb is good. Does this sound correct?

 

Yes that’s probably about the wattage they would use. Either the bulb is toast, the internal connects are hosed or the current aftermarket switch assemblies have omitted the bulb,

George

 

Well curiosity got the best of so I opened the Dorman switch. It does indeed have a bulb and across the contacts of the bulb itself I get 16 Ohms. Not sure why it did not light up when I had it in the truck. I get no reading, OL, when I test the pins on the switch itself.

I did the same test on a used switch and get no Ohms across the contacts of the bulb itself and again no reading when I test the pins in the switch itself. If I'm reading the schematic correctly it should be a direct circuit between pins H and G through the bulb meaning if the bulb is good I should get a reading off pins H and G, correct? This is of course if there is no break or disruption in the circuit board.

 

Try testing resistance between both sides of the bulb and each connector pin and see if there are dead shorts, IOW where does both sides of that bulb end up?


George

 

Just testing the used switch.
I've got .3 Ohms on each side of the bulb to pins G and H. So bad bulb?