Dome and cargo light help.

[Bug]

Been really trying to figure this out.  So the dome light and cargo light have their 12 volts to ground.  The light under the dash comes on when I open the door. But not the dome light.  No continuity between the whit wire and ground.  But are they on the same ground circuit as the under dash light.

On a side note only the lights on right side of of the instrument cluster light up.  Dimmer switch needs fussed with to get them to come on at all.   Are they related?

Bad switch?

Thanks in advance.

[Rapid Roy]

Welcome to the site.

[Henry]

Hi Bug:
What year is your truck? My 76 has the courtesy lamp (under dash light) power coming straight from the light switch (18-ORN-40B wire). The dome lamp and cargo lamp have power coming straight from the fuse panel (18-ORN-140 wire). So check your fuse for this one. The ground wires for the dome/cargo lamps (18 WHT-156 wires) join at a splice with the ground wires for the courtesy lamp, light switch, and door switches near the courtesy lamp. So if your circuit is the same as mine, I would check the splice near the courtesy lamp (SPLICE-156) and the courtesy lamp connector. You also would want to check the cargo lamp switch because I believe the ground wire for it splices to the dome light ground wire behind this switch, and then just the one 18-WHT-156 goes to the splice near the courtesy lamp.

I dont think the instrument backlights are related...sounds as if your rheostat for dimming in the light switch is going south or is dirty...or the contacts on the flex circuit connector (back side of instruments) are dirty, coming loose, or the flex circuit is breaking from age. Maybe just inspect this stuff and spray some electrical contact cleaner to the switch rheostat for a start.

Regards,
Henry

[bd]

Does the dome lamp illuminate with the doors closed when the headlamp switch is rotated fully CCW?  How about the under dash courtesy lamps?

[Bug]

Mine is a 77. The courtesy light does come on.  Both lights have 12 volts all the time.  It is just not getting to ground to complete the circuit I have read on here the light switch has jumper to the courtesy light ground just beating my head on this on one.

[bd]

So the courtesy lamps illuminate with the headlamp switch rotated CCW, but the dome lamp does not?

[Bug]

Never really checked the courtesy lamp when I turn the knob but it bows come on when I open the door.

[bd]

I got that.  Post what happens when the doors are closed and the headlamp switch is rotated all the way counterclockwise.

[bd]

Moving forward, if you ground the white wire near the dome lamp, does the dome lamp illuminate?  If the answer is "yes," remove the left door sill plate and check the condition of the white and orange wire pair beneath.  It's common for water to intrude compromised insulation and corrode the copper wires within, severing them (look for bluish-green copper salts).  If the wires are in good condition, inspect for terminal corrosion and loss of continuity through the left B-pillar inline connector.  If the problem remains elusive, trace the dome lamp white wire forward to its splice with the courtesy lamp white wires and ground it there to see if the dome lamp illuminates. 

FYI - If the dome and courtesy lamps were factory installed (none were added after-the-fact), rotating the headlamp switch fully CCW should illuminate all.  Otherwise, several variations in the wiring can exist.

[Bug]

Sorry it took so long to get back but yes the courtesy lamp does illuminate when it turned ccs.  I checked the wires they all looked good. Where is the splice exactly. I don’t see any splices I have three white wires that go into the courtesy bulb connection.  Thanks

[Bug]

Finally got it.  Broken wire.

[bd]

Good job!