I am finishing a 1979 f-150 project. All the interior lights are working. The wire from the dome light runs from dome light to under dash. It has been cut so there is no connector on it. Could someone please tell me where to plug it in so it works with the door jam switch and courtesy light switch. Thank you Ted

 

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 sheetmetal) 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.

 

What a great answer to the OP's question. Just want to say thank you to you Rich for always taking time to help others here on this forum. I am also without a working dome light and I will get out the multimeter in the morning and do as you say. Thanks again!

 

Rich: Here's another pic (upper) for your "collection."

The pic you posted is for the cargo lamp.

 

That was the dome light guidance that I received from FMC400 when I was working on my dome light issue.

ND yes I know it was the cargo light... but it gave him more info than he had in the 1st place, and the wire routing is close to the same.

And your pics explains it even more, so thanks for another pic.

 

Well... You've gone and done it again... Another superb post with the detail required for me to move forward with fixing "The Hulk". I was having issues with the in cab light coming on when opening the doors and the cargo light coming on period, but thanks to your post, the interior light is now coming! And although I haven't started tackling it yet, I'm sure I'll be able to deal with the cargo light as well now. THANKS!

Quick question though... Are there any other years of these trucks that have the same/as near as damn it cargo lights installed? I'm trying to find one to replace the one on the rear of my truck (cracked lense, dodgy gasket, bleached bezel etc, etc) but the only ones I've found so far have been online and they seem to want a kidney for them. There are a couple of 80's and 90's trucks parting out on CL, so would I be able to use a light from one of those? Just testing the water before I jump on buying one!

Thanks again Rich for showing me the way!

 

The left side of my headliner sags the slightest bit. One day while waiting in this sweltering Oklahoma heat I decided I'm gonna poke my finger in that hole. What I found was a thin black wire. It took me two days to figure out it was for the dome light. I lost sleep over it. Not really but I sure felt stupid lol. Hijack over, please resume your regularly scheduled programming.

 

So I'm looking into the problem that I've got with my cargo light and now I'm stumped!

I've blown the courtesy light fuse twice now and I'm struggling to understand why. So here's what's happened/I've found so far...

1/ Found the connector to the cargo light disconnected. Reconnected it, no light but blown fuse with the switch inside the cab in the "ON" position.
2/ Disconnected cargo light and replaced fuse. Tried again with a test lamp in the connector, getting supply to the cargo light connector...
3/ Tested continuity of the supply wire and found to be good.
4/ Tested continuity between supply to cargo light and chassis/ground... continuity found!?!?!?
5/ Checked switch and found continuity between ALL connections when in the "ON" position. When in the "OFF" position, only continuity between green/yellow connection and black/blue (two wires) connection.

Forgive me if I'm wrong, but this switch is supposed to switch the supply to the cargo light and not the ground right? How come I'm getting continuity to ground when the switch is in the "ON" position then? This doesn't make much sense to me... I would say that there is a ground in the light holder, but then when testing between the cab side of the light supply and the chassis, I wouldn't get anything right?

Just as a note, this light hasn't worked since I bought the truck and the only other thing I've done that could have affected this is changed the door jamb switch on the passenger door (thinking green/yellow wire that runs to door switches).

Someone please help!!!

 

Is the bulb installed in the cargo light socket? If so, that's your path to ground.

 

I actually thought about that and removed the bulb to make sure I didn't have a path to ground that way.

I was meaning that I was getting continuity to ground when testing on the supply side to the light, as in the wire that runs from the switch to the light with the light disconnected. But would the multimeter act as a component in that regard and give the continuity? I don't think so, but now I'm not sure.

From what I've read and can figure out, I should only have 12V at that connection and shouldn't have circuit continuity to ground on the cab? The only other thing I've noticed is that I don't blow the fuse when the cargo light is disconnected, regardless of the switch position, and do when it's connected again. Based on this, I can only guess that the actual light fitting is shorted out and that's what's causing the issues. It would make sense as the gasket is knackered and has been letting water in behind the light fitting for some time now!

I'm going to replace the light fitting and see if the situation is resolved with that, but if not I'm going to have to dig further!

 

Yeah, sounds like you've definitely got a short there.

 

I'm glad you got it figured man! These dudes are smart.
So, it's not hijacking if you are fixed up, plus don't really want to start a new thread on the same topic


I went to the JY and grabbed a few door jabs as mine were rusted "door closed" position. My dome light itself works perfectly, with the **** to turn it on. Each truck I grabbed the jabs from - the drivers side has 3 wires on the jab and the passenger has 2 wires. I'm sure there is a reason. However, I got these JY ones cleaned up and wires stripped ready to go. I remove my drivers side and it only has 2 wires, black and green - no red like my junkyard finds. Thinking my JY finds were from like 80s ford trucks. So, Am I still good with just the 2 wires on both sides you think?

this is my drivers side jab.

 

check screws on cab light are tight OR have not been overtightened and broken off the ground tab (if I recall right), only one of them is the ground screw

I had to replace a dome light assembly once, it looked fine but was broken, only replaced the part that was screwed to the truck and everything worked again

cab light assembly has a plug to unplug to replace cab light assembly, can also test at the point for power to check the wiring is good between the switch and the cab light, and then retest with assembly in place

cargo light wiring plugs into dome light circuit wiring on driver side, need to pull cluster out to get at dome/cargo wiring light circuit plugin, you can test within that plug to make sure you getting power to that point and then if getting power you can test at the door jamb switches and cab light itself

cargo light is a metal piece on 73-77 cargo lights, apparently it is a different design for 78-79s
77&79F250's diagram shows the 73/77 style. I am not sure of the 78-79 construction but like you say the seal is old and water has been getting in then I would check on that

the headliner trim is held in with metal screws through a metal roof, if one of those were to puncture the dome/cargo wires that run along the driver side then that could be a probable cause of the shorting

also the cargo light has a ground wire with ring terminal to check it is grounding properly too

I added a cargo light to a truck and hit the switch and had no light, the light socket was slightly corroded and the bulb was burned out, I sanded socket and replaced bulb and it worked

make sure of the position you left the headlight switch in, on to the left to manually turn on cab light or in natural position for when driving

ALSO: the under dash lights (if equipped) one illuminating each footwell, also plug into the doorjamb circuit, also in the same place that the cargo light plugs into in behind the cluster to the left, near the headlight switch

ALSO: the cig lighter uses a green/yellow constant power wire as well (I'm not sure if it is the same circuit, I do believe it is the same as dome light)

Whew! I think that covers it...

 

So you have the instrument cluster out and can see the wire coming through the hole under the drivers side A-pillar, and the connector was cut at that point? or is it hanging out from under the dash?

Have you solved it yet?

 

The extra wire on the later-model ones is probably for the door-open/key-on buzzer. You're fine just using two of the wires, as long as you tape off the other one so it's safe (it'll be hot when the door's open). If your door alignment doesn't match up with the used switches, you can buy new ones - they're auto-adjusting the first time you close the door.