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My dome light solution on 05 Ranger XLT; partial rewire to new light.


Green05

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Hi!
My 05 Ranger XLT has issues where sometimes the dome light refuses to power on. This is from the dome switch and the dimmer. I understand that the door switches work. They are to connect to the ground and turn off/the ground NOT the power. I don't feel like doing a wire trace and I am not going to replace a defective SJB (Smart Junction Box).

So... I am going to find the wires to the door switch on both sides, sever the wire going to the SJB or its relay, and run it to a second lamp in the dome fixture. That will avoid running 24v to the existing dome accidentally. Next I plan to take the constant-on 12v+ and run it to the secondary fixture.

I already have a switch going to a 12v LED marine lamp for the passenger well. That way my passenger, for now, won't howl about going into a darkened truck. I want to tap into the constant-on and run it through the headliner to my second fixture.

Am I blowing smoke?

Hope I didn't post twice; didn't see my post earlier so I wondered.
 


ericbphoto

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Where do you think 24 volts is going to come from? The vast majority of Ford Rangers are 12volts. You are not going to create 24 volts just by running a second wire to a light.

If it were me, I would troubleshoot and repair the original circuit. But I realize everyone's skillset is different and I'm not there to help you in person. With a little more information, someone here might be able to help you understand and fix the circuit.

Does the light come on when you open the doors?
Does the light come on when you turn on the switch when the doors are closed?
Have you tried a new bulb?
Is the bulb tight in its holder/socket?
Have you made sure there aren't any loose connections?
Have you Google searched for a wiring diagram?

On that new of a truck, I believe you will find that there are some relays involved - battery saver relay and interior lamps relay. You could check those and make sure they are working properly.
 
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Green05

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Won't two legs of 12v in parallel create 24v? Or is that just on AC power?

As for the other questions:
Does the light come on when you open the doors? Sometimes
Does the light come on when you turn on the switch when the doors are closed?
Sometimes
Have you tried a new bulb?
I will but only because the existing bulb sometimes shows semi-bright.
Is the bulb tight in its holder/socket? Yes
Have you made sure there aren't any loose connections? I haven't checked the wiring but I did notice that the passenger door switch was not working at all. The previous owner said the door would not trigger the dome light. I replaced the switch but got a sometimes on/sometimes off issue.

Have you Google searched for a wiring diagram? I have tried this but will try again. I saw nothing denoting color of wires or where they lead.

Thanks.
 
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ericbphoto

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Ford Ranger
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3.0L
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Manual
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4WD
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6"
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My credo
In theory, theory and practice are the same. In practice, they are different.
Won't two legs of 12v in parallel create 24v? Or is that just on AC power?

As for the other questions:
Does the light come on when you open the doors? Sometimes
Does the light come on when you turn on the switch when the doors are closed?
Sometimes
Have you tried a new bulb?
I will but only because the existing bulb sometimes shows semi-bright.
Is the bulb tight in its holder/socket? Yes
Have you made sure there aren't any loose connections? I haven't checked the wiring but I did notice that the passenger door switch was not working at all. The previous owner said the door would not trigger the dome light. I replaced the switch but got a sometimes on/sometimes off issue.

Have you Google searched for a wiring diagram? I have tried this but will try again. I saw nothing denoting color of wires or where they lead.

Thanks.
No. You only have one 12 volt battery. So, two positive wires coming from the same battery will not add up to 24 volts. If you put TWO 12 volt batteries in SERIES you can create 24 volts. But there is no reason to do that. It is the same for A.C. power. Voltage in SERIES adds together. Current in parallel adds together. Resistance in SERIES adds together. But resistance in parallel adds funny to make a lower resistance than either of the single resistances alone. But Ohms Law is for another lesson.

Your statements about the light working intermittently and sometimes being dim really make it sound like you have a loose connection somewhere. I will try to dig up some wiring info tomorrow when I get to a real computer. If you can find the relays and gem module and make sure they are all connected firmly, that could be a start. Also make sure all the mounting screws for the light are tight. Those screws are often used to connect the fixture to the wires and ground. If you take the fixture down, you will see what color wires are in the circuit.

Eric B
 

ericbphoto

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1993
Make / Model
Ford Ranger
Engine Type
3.0 V6
Engine Size
3.0L
Transmission
Manual
2WD / 4WD
4WD
Total Lift
6"
Tire Size
35"
My credo
In theory, theory and practice are the same. In practice, they are different.
Wow. I am having trouble finding an online wiring diagram for that, especially one that shows the door jamb switches. I suspect that on a vehicle that new, your dome light is controlled by an interior lighting relay, GEM module, and possibly a battery saver relay. The door jamb switches may just be sending a control signal to the module containing the lighting relay(s) and therefore, not directly in the current path to or from the light. You may find wiring diagrams in a Chilton or Haynes manual. It would be worth a few bucks or a trip to the library. Again, it's probably a simple loose connection or a relay going bad. You would probably find it by spending a bit of time checking those things. Rigging up some wierd home-grown circuit will probably take longer and if you aren't good with electricity, could cause you more trouble.
 

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