Dome, Cargo, and Courtesy Light Mystery

[green72s]

Hello,

I'm working on my '79 Sierra. I recently completed some small projects on the truck. I repainted the instrument needles, and replaced the following items.

• the clock in the instrument cluster
• instrument light bulbs behind the cluster
• courtesy light bulb under the dash
• dome light bulb
• cargo light bulb

Since adding these new parts and re-installing the instrument cluster there are strange things happening with the dome light, courtesy lights, and cargo light. All the instrument lights work, and the clock worked for a while, that's might be a different issue.

Here's what happens when everything is connected.
Under dash courtesy light
The courtesy light under the dash almost works fine, it turns on when either of the doors is open and mostly turns off when the both doors are closed. What's strange is that when both doors are closed the courtesy light turns on although it is very dim.

Dome light
The dome light does do not work when either of the doors are open. The dome light does not work when the light switch is moved to the dome light on position. The dome light turns on but is very dim when both doors are closed.

Cargo light
Same behavior as dome light, does not turn on at all except when both doors are closed, then it turns on but is very dim.

What happens when I disconnect the dome light and cargo light wiring harness just behind the driver (the orange and white connections)
The under dash courtesy light works exactly as it should, now turning off completely when both doors are closed.

Tests I've done
The dome light bulb is good
The cargo light bulb is good
I cleaned the ground connection between the cargo light housing and the cab.
Was going to clean the ground connection between the dome light housing and the cab but noticed that the dome light housing is plastic, so it must ground some other way.
I cleaned and checked the passenger side door switch for the dome light.
I did a visual inspection on the dome light and cargo light wiring harnes as it runs under the driver sill plate.
With the upper part of the dome light and cargo light wiring harness disconnected (behind the driver), I checked for voltage: the orange wire shows .08 volts with the doors open and with the doors closed, the orange wire shows .01 volts when the doors are open and 12.24 volts when the doors are closed.
I did lots of continuity tests between the beginning of the upper dome light and cargo light wiring harness (behind the drive) and the top of the wiring harness at the dome light and cargo light; everything seems to be OK.
The cargo light switch doesn't work great, you have to finesse it to get it to allow current to flow through it (checked for continuity), so for the time being I bypassed the cargo switch by connecting a wire between the two connectors.

I apologize that there is so much to read here, but wanted to answer as many questions ahead of time.

I'd really like to get this issue ironed out. The truck is so close to having everything working.

Thanks!