Dome Light Won't Turn OFF

My 94 Ford Tempo has had a trouble with the dome light for some time. It won’t turn off no matter the doors open or close. When I was aware of the fault, the dome light bulb and its socket had been burnt due to the high temperature arising from the light bulb being ON for long time. It could be a hazard and I don’t understand why Ford didn’t make a recall.

Without the repair manual, I can only do something that every technician does. The first thing is the trigger switches that is expected to be pushed by the edge of the door when the door is closed.

One of the trigger switches was found to be sticky. So I sprayed WD40 on it, pressed and released the button repeatedly until the stickiness went. Tested it with the doors closed, the dome light still won’t turn off! Then I unbolted the trigger switches and test if any of the switches was faulty. They were all good. They are momentary switches. The contacts are open when the button is pressed (door closed) and closed when the button is released (door open). Then, I disconnected the switches and tested the wires. What the hell! One pair of the wire was found shorted somewhere. I couldn’t identify visually where the short was because the wires run inside flexible tubing under the dash. I pulled and wiggled the wires; hopefully the short could be separated that way. No luck! No idea what to do next. Put the switches back and left it for then.

Did some internet search some day later; I found a post that it mentioned the dash light dimmer also controls the dome light operation. Then I tried it. It works! What the hell! The dome light is not faulty; only that its control is confusing! The head lights, the dash light and the dome light share one control knob. 

Pull the knob outward will turn on the head light; push it down will turn it off. Turn the knob clockwise will dim the dash light. Turn it all the way anti-clockwise will set the dash light the brightest. Turn it anti-clockwise further until it makes a “click” sound will turn the dome light on, regardless the status of the doors. The knob is so easy to set it wrong inadvertently!

In order to prevent from burning the dome light bulb again, I changed it to white LEDs. The LEDs are taken from a retired LED Christmas tree. Each LED has its diffuser and its light is much softer than that of a raw LED. Each LED takes 3.6V, so putting 3 LEDs in series with 2 rectifier diodes makes it 12V rating. I put two strings in parallel and the combination of the LED strings only takes 80mA. It won’t burn anything or drain the battery flat overnight if the same mistake is made again, hence safer.

The trunk light is controlled by a tilt switch which is inside the trunk light connector. It makes the contact when the trunk lid is lift. If the car is parked on the road downhill, the tilt switch may activate the trunk light and drain the battery.

This picture shows you that the burnt light bulb was modified to a connector for the LED strings.

33 LEDs Dome Light Upgrade (May 14, 2008)

The dome light is too dim. I upgraded it to 33 LEDs version a week later. See the pictures below.

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End of the project

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