66 C10 Dome light

[rbkanco]

Getting the wiring put back after paint shop. The dome light has a white and orange wire. They are both hot at the switch, and the light. Shouldn't only the orange wire be hot until switch is on? Meaning the switch is bad? The light bulb is new and it doesn't come on even though power goes through it. Which seems strange.

[_Ogre]

just typed this for another thread
this is for a 67 but same wire colors and switch connections (different switch)
if you pull the bulb out the orange wire should be hot and the white wire is grounded
by rotating the headlight switch or thru the door switches if so equipped

Could anyone tell me how the factory set up works?

the oem setup works by running a hot wire to the light and switching the ground
the orange wire from your fuse panel to the headlight switch also powers the dome light
the white wire is grounded by rotating the headlight switch or thru a door pin
door switches were optional and easy to add by tapping into the white wire

a lot of previous owners can't understand the switched ground and add the toggle switch

wiring diagram for your 67



door pin switches

[rbkanco]

Thanks Ogre. Sounds like a bad switch if orange and white are always hot and can't get interruption no matter how far I turn either direction.

[_Ogre]

the white wire will be hot until the bulb is removed
make sure the white wire is connected to the correct lug on the headlight switch
a quick test is to unplug the white wire from the headlight switch and ground the wire

pull the headlight switch to check the function of the white ground connection
this is a standard gm headlight switch; you can see the rheostat for the dash lights
plus the bare copper for the dome light; turn the knob and the bare copper grounds to the switch housing
you may need to adjust the ground to make it work properly

[rbkanco]

So I'm confused. The white carries current to bulb, then orange back to switch. if contact adjusted right and switch is on then current goes to fuse box making circuit and bulb = lights? On your test... when the white is grounded and you pull on the headlights are you checking if the headlights come on or dome light. Sorry I'm dense.

[VetteVet]

Originally Posted by rbkanco

So I'm confused. The white carries current to bulb, then orange back to switch. if contact adjusted right and switch is on then current goes to fuse box making circuit and bulb = lights? On your test... when the white is grounded and you pull on the headlights are you checking if the headlights come on or dome light. Sorry I'm dense.

No the orange wire is the hot wire. It feeds the light 12 volts whenever the battery is connected and the fuse in the fuse panel is inserted and good.

The 12 volts goes through the light and into the white wire so you are reading 12 volts on the white wire. If you pull the bulb you will still read 12 volts on the orange wire but the white wire will be dead.

When power goes through the orange wire and into the bulb, the white wire becomes the path back to ground, and when it touches the truck metal body, the circuit is complete, and the voltage runs from battery positive through the orange wire, lights the dome light bulb and returns back to the negative battery terminal through the white wire (ground). You can interrupt the current path on either the positive side, or the negative side, with a switch and control the light or any other accessory. Most things are controlled on the positive side, but the wipers, horn and the courtesy lights are three things that are switched on the ground side.

You don't have to pull the headlights on to check the dome light. Like Ogre says just rotate the knob all the way CW and the dome light should come on because the headlight switch grounds the white wire for the dome light.

[rbkanco]

Thanks VV. That is what I was thinking. So if orange and white are hot it must be a bad switch. As I can never turn it off.

[_Ogre]

As I can never turn it off.

re-read vettevet's post, the orange wire to the dome light is always hot
the dome light turns on when you ground the white wire; thru the headlight switch or door pins

this is standard gm dome light wiring method and the reason they do this is so that
either the headlight switch (rotated) or any door pin may be used to ground the circuit
in a station wagon you would have 5 door pins (one for tailgate) and this simplified the circuit

similar to a glove box light: the bulb always has 12v+ to it, when you open the door the switch pin grounds the circuit
this diagram shows the dome light circuit

[rbkanco]

Thanks guys. When you are unsure of how things are supposed to work it makes it hard figuring out what is wrong.

[_Ogre]

that's why we're here
btw... i haven't worked on a new truck in over 30 years, mine is a 58
i just read the wiring diagrams and repost pics from vettevet's threads