After getting a mustang dome at a wrecker today, I thought I'd try and and see if I could try and make all three bulbs illuminate when the door opens, rather than two of the three sitting unused for the majority of the time.

This method leaves the vehicle's wiring untouched and only modifies the dome. Both switches still function as normal without any side effects. Cheap and easy to do, shouldn't take longer than an hour. Of course, I nor FordRangerForums is responsible for any damage to your vehicle. Proceed at your own risk.

Things you'll need.
Wire. A few feet should do. I wouldn't go any thinner than the dome light's original wiring, but not too thick either.
Two diodes. These diodes should work. Click Here (SB5100 Diode)
A pair of needle nose pliers wouldn't be a bad idea.
A soldering iron and solder
A power supply capable of delivering half an amp at 12 volts or better (for testing purposes)
A multimeter.
A screwdriver
And of course, the dome.

First off, we need to pop the dome apart. To do this, there are four Philips screws, location marked by the four red X's.



Remove those and the white plastic should come right out. If it doesn't, gently push on one of the switches to pop it free. Fear not, there aren't any pieces that are going to go flying.

Now turn the board around so that it looks like this.



Note the bolts numbered One, two, and three. You'll be testing your dome light with these bolts. You should find the following is true.
1 - Constant Power
2 - Ground
3 - Door Circuit

If it isn't, adjust accordingly. Be careful to wire this up correctly! If you don't, you risk burning your truck to the ground.

You should see that the various bulb's terminals are marked. We'll be only making use of three of the contacts.

Yellow boxes with a black X inside designate ground. Blue boxes designate the door circuit. Green and orange boxes designate the 'always hot' lead.

After you're sure that the domelight ohms out properly, we'll start building the circuit.

This is where some alligator-clipped jumper wires will be handy.

Take your diodes and connect them as shown by the purple 'wire' going from mark to mark. Make sure to orient them correctly, otherwise it won't work properly. They should allow current to flow from the center festoon bulb but not back to it.
Note that the orientation shown may or may not be correct for your specific diode. Simply flip the diode around if it doesn't work at first.

Once you have your jumper wires connected, apply power and see if the lamps illuminate properly. They should be on regardless of what position the switch is in. But of course, if terminal 1 is powered and 3 is left open, they should operate only by the switches and the center bulb should be dark no matter what way the switches are pointing.

All three bulbs should only illuminate when terminal three is powered.

If it works, take the bulbs out and solder on some wire to the outside of the festoon's clips, taking care to route the wire so it doesn't get in the way of anything or potentially shorting anything out. Once that's done, test it again to make sure it still works.

If it does work, the following should be true, spoken as if it were mounted in the truck.
- When the door is open, all three bulbs come on regardless of what state either switch is in.
- When the door is closed, both outer bulbs should turn on and off independently of each other. The center festoon bulb should not be active until either the door is opened or the cargo light switch is turned on.
- When the cargo light switch is on, all three bulbs should illuminate, again regardless of what position either switch is in.

If this all is true then you're done. I, however, would recommend leaving the domelight running outside the truck for an hour with all three bulbs on. There's a reason for this.
Diodes have a forward voltage and with this produce heat. If they get too hot to hold onto you may need different diodes. You should be able to hold the wires and the diode barehanded indefinitely. Cool to the touch is okay, warm to the touch is okay, but hot enough that you can't hold it is a warning sign. Swapping the diodes may be necessary, but shouldn't be.

Warnings:
-If you don't remove the bulbs before soldering to the contacts, you'll end up ruining the bulb. While the bulbs are cheap, you may be mislead into thinking you damaged the actual dome circuit by accident.

-Make sure your diodes can handle upwards of 16 volts and at least five amps of current each. While at most you'll see 15 volts from your truck and it doesn't draw 5 amps, stick to these parameters otherwise you may find yourself with a smelly, hot, mess of melted diodes, which could potentially set your headliner on fire.

-When soldering, be careful not to melt the plastic housing.

-It is advisable to use heatshrink tubing over the diode to prevent it's leads from shorting out. However, leave the inner bulb contact uncovered otherwise the bulb may not receive power.

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This is the first 'how to' I've ever done, so I hope it's easy to understand. If there is any confusion, please, do not hesitate to tell me so I can clear it up. I hope you enjoy your modded dome light.

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While I was browsing YouTube, I was watching a couple videos about diodes. Picking out diodes can be very tricky, so I thought I would provide some helpful information on the subject.


In this application, a Zener diode is the worst type of diode to use, and the video on it will explain why. I'd hate to hear somebody burned their truck down to the ground, so I thought I'd try and help to prevent that with a little more knowledge explained by someone more qualified than me.

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I think you nailed it!
Great write-up & Thank You

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Black '98 XLT 4.0 liter, super/extended cab, 4X4, 5 speed manual

*Mods & Pseudo Mods*
Sony head unit, Expo OHC, Uniden CB, 16" Wheels from a 2002 Expo Sport Trac/255-0R16 tires

So can you still use the map lights independently?

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@Bob C.
Sure can.

@Grampy

Thanks, and you're welcome.

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Great write up! The pics make it very easy to understand and your detailed how-to is simple to follow. Nice first how-to!

nice write-up!

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Thanks to the both of you. Glad to see it's going over well.

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Great! Thanks for the write up,nice job!

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Where would we find these at?
Part numbers would be great for those of us who are that familiar with diode specs

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Black '98 XLT 4.0 liter, super/extended cab, 4X4, 5 speed manual

*Mods & Pseudo Mods*
Sony head unit, Expo OHC, Uniden CB, 16" Wheels from a 2002 Expo Sport Trac/255-0R16 tires

If you google the part number on ebay or amazon, you should be able to find some.

http://www.amazon.com/s/ref=nb_sb_no...s=sb5100+diode

http://www.ebay.com/sch/i.html?_from...diode&_sacat=0

Also, the diode's part number is sb5100. Apparently it's also a modem's model number.

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Cool Thanks!
I'm too impatient to wait until sometime September for the USPS to loose the package while rowing their outrigger from China. LOL
The USPS and I don't play well together if that wasn't apparent.
Looks like I might have a little "travel time" ahead of me, as our local Radio Shack went into the cell phone business, and couldn't compete with ATT & Verizon lol.

There are however a couple of electronic repair shops close enough to check out. (I'm about 10 miles from town)

So if while on my quest, if I run across anything over 16V & rated at 5A, I'd be good to go?

*** Just Imagine ***
Buggman LEDs in the dome & the OHC on a slightly foggy night, would make the truck light up like a Scy Fy flick!

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Black '98 XLT 4.0 liter, super/extended cab, 4X4, 5 speed manual

*Mods & Pseudo Mods*
Sony head unit, Expo OHC, Uniden CB, 16" Wheels from a 2002 Expo Sport Trac/255-0R16 tires

As long as it can handle a minimum of 16V and 5A, you're good to go. I doubt that dome light would ever draw anywhere near 5A, but it makes for a good safety margin. Also worth noting that the SB5100 is a Schottky diode, not a regular silicon diode.

If you're not familiar with diodes, the only real difference is a lower foward voltage, so less heat. I'm sure one could get by with a regular silicon diode though with the same rating.

And yeah, those LEDs do sound rather nice. I may have to buy a pair from him some day down the road. They're certainly popular.

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