Hello everyone,I've got a 1980 F100.Awhile back I had added the Dome-Map/Cargo light harness from a donor 86 F150.My truck had originally came with just a dome light and no map or cargo lights.Anyways,today I finally got around to cutting the hole in the cab.When I had gone to get the cargo light harness I was lucky to find a mint cargo light cover with perfect rubber gasket off of a 92.Anyways,I cut the hole,drilled the screw holes,and put it in.Fits like a dream.I turned the headlight switch all the way to the left to turn it on.It worked perfectly.But here's my problem.My dad has an 87 F150,and I could've sworn that the Cargo light is supposed to come on when the doors are open.Mine doesn't.It just comes on when the dome light is turned on.Why is this?My truck doesn't have the passenger side door open button.Is this maybe why it doesn't come on when the doors are open?All help is greatly appreciated!!!!

 

My 80 had a factory installed cargo light and it only came on with the headlight switch to the left.

It must have had some sort of lighting group option, because it had the maplights with the dome light, the cargo light, the amber roof running lights on the top, and the recoil trouble light under the hood.

 

Yes, it's working exactly how it should work. It only is supposed to come on with the headlamp switch turned to the left.

There is a inline diode in the cargo light wire and that isolates power and only lets it go one way.

The dome light should work with the door open and with the headlamp switch, but the cargo light should only work with the headlamp switch.

The power is fed to the Cargo light like this and flows with the arrows....

Headlamp switch --->, Cargo Light --->, inline diode -->, dome lamp --->, door switches ---->.

As you see, power passes through the inline diode in this direction to light the dome lamp.

Then you have power fed to the dome lamp from the door switches like this....

Door switches--->, Dome Lamp----> | <-- inline diode.

The inline diode blocks the power flowing in this direction, so it never reaches the Cargo Lamp.



However, to make things confusing, the inline diode tends to fail and alow power to flow in both directions, alowing the cargo lamp to turn on with the door switches. This is what most likely happened to your father's 87. It also will not hurt anything, his cargo light will light with the door open is all.

You may notice someday that your cargo light will turn on with the door someday in the future too.


hope this helps explain whats going on.

 

So is the cargo light not supposed to come on for any 80-96 truck?Cause i asked a buddy and he said his 93 Bronco and his brother's 94 F150 cargo lights both come on when the doors are open.

But I do understand why it doesn't come one.Thanks alot for the help man.It's greatly appreciated.

 

Yes that's correct. The In-line diode is supposed to stop the cargo light from coming on with the door switches.


Yes, the in-line diode is prone to failure. Why yours will probably come on with the doors someday.

Here is the diagram of the courtesy lamp group circuts. You can see the in-line diode on the wire between the cargo lamp and the dome lamp. It only alows power to go one way.



Glad to help

 

Okay that clears alot up.I really appreciate it.Happy New Year to you all!