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Porsche 993: Why Won't My Interior Light Go On/Off?

A malfunctioning interior light causes inconvenience. Learn how to detect the sources of interior light failure and their solutions.

By James Karuga - April 13, 2015

This article applies to the Porsche 993 (1993-1998).

The interior light comes in handy when it's dark and you have to look for something in the car or locate the ignition key and barrel. Most cars have the interior light on the roof and on the door panels. For most cars, Porsche 993 included, the light is set to go on, when doors are opened, and off, when the doors are closed. When they malfunction, the aforementioned actions won't occur, and that can be a source of nuisance to any car owner. This article highlights some causes of interior light malfunction for the 993 and possible solutions. With help from this article, you will be able to quickly trace the problem and sort it without guessing.

Figure 1. 993 Turbo interior.

This article assumes the interior/dome bulbs are working and not blown.

Step 1 – Is the door contact switch working?

The action of closing the door of the 993 is supposed to switch off the interior light. But if the door contact switch on the door panel is faulty, then the interior light remains on when the door is closed. A faulty door contact switch loses the grounding effect that turns off the interior light. Connecting a voltage tester on the switch plugs after removing the faulty switch and turning the tester on and off helps you narrow the problem to a faulty switch. If the door contact switch is worn out, replacing it costs less than $55.

Figure 2. Door contact switch.

Pro Tip

An interior light that doesn't go off when it's supposed to drains power from the battery.

Step 2 – Is the hood properly closed?

The interior light won't go off if the hood is not properly closed when the doors are. If the interior light remains on after you properly close the hood, it could be the case that the hood release latch or latch switch button are faulty. Hence, one or both may require replacing. A new hood release latch for the 993 costs from $50, and the button from $10 onwards.

Figure 3. Inspect the hood latch.

If the issue still persists after confirming the functionality of the hood latch, move to the door switches.

Step 3 – How is the door microswitch condition?

There are instances where the interior light fails to come on when doors are open. If that happens, check the condition of the door actuator microswitch. When the door actuator microswitch is faulty, it fails to detect the open door condition as it should, and the interior light won't switch on. Faults in the microswitch also affect the central locking mechanism of your 993. You can detect a microswitch problem if, after leaving the keys in the ignition and after opening the door, the car fails to give a warning sound. The solution is replacing the faulty actuator microswitch with a new one which costs less than $100.

Figure 4. Door microswitch.

Pro Tip

Also check the condition of the wiring connected to the door actuator microswitch; if it's faulty, the switch won't work.

Step 4 – Are the interior light fuses blown?

If the interior lights are not turning on, check to see if their fuses are blown. The fuses blow up if current is excess or wire casings have peeled off and are touching the ground parts. Also, if the 993 is fitted with aftermarket components, those overload the circuit, causing the interior light fuses to blow up.

Figure 5. Check interior light wiring.

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