Hey guys, 2004 XLT here. I only got it a couple months ago, and it hasn't worked since I got it, so I have no record of what the P/O could've done to break it.

I can't get my dome light to get any voltage in any way (using my multimeter for all this diagnosis, rather than a bulb). I have a black wire with a blue stripe going into one screw terminal, and the ground is just screwed into the chassis.
I've tried every combination to get voltage to the receptacle, but nothing has worked. Keys out, keys in, doors open, dimmer switch clicked up. The fuse is fine too, I'm not sure exactly which one it is, but none of my fuses are blown, I checked every one in the passenger floor kick panel and every one in the fuse box under the hood.

Any help?
At this point the only thing I can think of it a cut or melted wire, which I guess I'll be checking for when I remove the headliner to fix the fabric. but any suggestions for me to figure it out before then would be much appreicated.
It's driving me nuts not having an interior light in the car, I'm about two seconds away from duct taping a battery powered light to the roof haha.

 

It's fuse 13 in cab fuse box, pull it out and test the fuse terminals, one should have 12volts all the time, key doesn't matter
If not that's the problem

There are two 12volt feeds to the dome light's black/blue wire
Door open switch activates the a relay that sends 12volts to that wire
Dimmer wheel when turned "up" all the way sends 12volts to that wire
Key on or off doesn't matter for either of these

If Dimmer wheel ALSO doesn't turn on dome light then problem may be in the SJB(smart junction box) or its connectors

Does the Door Ajar light work?
If not the door open switch is not working
Try passenger door

SJB is the Body Computer, cab fuse box is part of the SJB, article here has pictures of the SJB: https://www.therangerstation.com/tec...horn_mod.shtml

It has 4 large connectors
These connectors have been know to corrode , like this: https://i1.wp.com/sparkys-answers.co...0/DSC09929.jpg
But in any case this is where the 12volts comes from on the black/blue wire
Connector numbers seen here: https://ww2-secure.justanswer.com/up...636_ranger.gif

Black/blue wire is on connector C2280B pin 14

 

Wow that's super helpful information!
I'll double check that fuse 13 is getting 12V tomorrow, but I know that I got continuity in that fuse when I checked it.
Both of my door sensors work, as I've had it ding at me for not shutting the door hard enough a handful of times, I believe on both sides. Dimmer wheel doesnt do it either.
I'll remove the SJB tomorrow and take a look around and see what I can find. Thank you so much! That's really helpful articles on the topic

 

Well I don’t have power to the blue and black wire on the SJB. Now what?
I did confirm continuity from that pin to the wire at the light, so that’s good, doesn’t seem to be to an issue with a snipped wire or anything, but rather an issue with the SJB. Not sure what to do from here though…

 

Check if the Black/Pink wire, near it, at pin 10 has 12v with Dimmer turned on

And see if fuse 13 has 12v

The relays in the SJB are not serviceable parts

I guess last thing will be to pull the connector and see if there is corrosion

Used SJBs are usually not hard to find, there were two models, WITH keyless entry and without keyless entry

Go to car-part.com: https://www.car-part.com/

2004
Ford Ranger
Computer box not engine
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You want "multifunction" keyless or no keyless, if you don't have keyless then you can't add it just by using an SJB, there are more parts needed, lol
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Used one shouldn't be too expensive, $40-$75

 

I’m in for the night, so I’ll Check voltages tomorrow. But I did bring the SJB in with me and ripped it open.






theres some slight corrosion on the C2280c connector, but not much. Could easily be cleaned up. But No visible corrosion on the C2280b connector, where the wire in question connects. Ripping it open showed no additional signs of corrosion.

is there a way to visually identify the two different SJBs? I’ve been pulling parts from the trucks at the junkyard, which are quite plentiful. I have no doubts I could find an SJB in good condition, as long as I can find the right one. I have keyless entry.

 

Well, connector C has the main ground for those relays, also 2 or 3 other wires for it

And in the one pic there is corrosion around the pins at the top

There should be a part number on your SJB that starts with 4L5T-15604-XX
The XX is the model
Might be a sticker label

4 = 2004
L5 = Ranger/Mazda B-series
T = department

15604 = Body Computer(multifunction)

XX equal keyless entry or no keyless entry
I saw AK and AG as keyless entry models online


I would use Q-tips and isopropyl alcohol to clean up corrosion, don't forget inside the connectors
And reinstall

 

Great! I’ll take a crack at cleaning this up and go from there. Thanks so much for your help!