1975 F250 Highboy, all stock.

I know illuminating the dome light from the headlamp switch lights up the dome light and the underdash lights if present but does not turn on the cargo light.

Does illuminating the stock cargo lamp from the cargo lamp switch illuminate the cargo lamp AND the interior dome light simultaneously?
Thanks
Tbruz

 

On my 78 turning on the cargo/back of the cab bed light with the switch mounted on the dvrs side B pillar and above seat belt retractor, does NOT turn on the interior dome light or the courtesy under dash lights.

 

The cargo light switch in my 74 only turns on the cargo light.

 

I installed this cargo light(truck did not have one from factory) using a stock harness, stock light and a stock switch.
Not sure what I got wrong to cause both the interior dome and the cargo light to turn on from the cargo light switch; there is only one connection.
Tbruz

 

Better to have it all work, than not at all. Here is some words of wisdom from FMC400 when I was working my dome light issue.

For the*dome*light*wire, hot-at-all-times power comes goes to the headlight switch as a GREEN with YELLOW stripe wire.*Dome*light*power comes back out as a BLACK with BLUE stripe wire. The same color scheme is used at the door jamb switches. BLACK with BLUE stripe runs out to the actual*dome*light. BLUE with a RED stripe is instrument panel illumination. It comes out of the headlight switch to the fuse box, leaves the fuse box again as the same color and is distributed throughout the dash.

There is no ground connection to the*dome*light*switches or the headlight switches. These switches switch power, not ground.
1) Make sure you have 12 volts on both sides of the courtesy lamp fuse. This circuit is hot at all times, so it doesn't make a difference what position the key is in. If you have power on only one side, replace the fuse. If you don't have power on either side, then there is other work to do first.

2) Pull the*dome*light*switches out and remove them. Make sure the terminal for the GREEN with YELLOW stripe wire in the connector has power.

3) Check the*dome*light*switches for continuity. With the plunger all the way out (switch CLOSED), the switch should be shorted. With the plunger pushed all the way in (switch OPEN), the switch should be open. If not, replace the switch.

4) With power to the switch proven to be good, and the switches proven to be good, the*dome*light*should*light*up. If the*dome*light*does not*light*up, remove the cover and check for power at the*dome*light*(not the side that's permanently grounded to sheet metal) with the door OPEN. If you have power here, yet the bulb does not*light*up, replace the bulb.

This will prove out the door-side; if you get to the point that the doors turn the*light*on but the headlight switch will not, then we can cross that bridge.

 

Ok, think I have this figured out and need a huge favor from one of you folks whose cargo lights work correctly.
With my switch out and using a jumper wire on the harness, the lights work correctly in that only the cargo light come on, not both cargo and dome.

Makes me think my cargo light switch in the cab is bad.

When I check the removed switch for continuity across the three pins it works correctly in the off position(dome and cargo are off as indicated by the switch and no continuity between any of the three blades (pins).
However in the on position. I have continuity from the single blade(12v power feed) on the switch to BOTH of the other two blades on the switch. Im thinking maybe I should have continuity between only the single pin and one of the other two, but not both?

Can someone throw a meter on their properly working removed switch and advise what they see for continuity in the off and on positions.
Many thanks
Tbruz