I' ve done it another way
Question
Why won' t the engine bay light on my 944 work?
Answer
The principle behind the operation of the engine bay light is that within the housing there is a mercury tilt switch. When the bonnet is closed the mercury does not make contact with the live feed and conversely when it is open the mercury makes contact and completes the circuit. It should be noted that the light will only illuminate if the sidelights are switched on.
If the light is not working then the procedure outlined as follows should work in most cases:
1. Make a small cut in the wire leading into the bulb holder to expose the inner wire. Using a circuit tester, make sure that a current is actually being delivered to the bulb holder, not forgetting to have the sidelights on of course! If you have no current, check the sidelight fuses. If still none consult a qualified vehicle electrician as to the cause before continuing with this fix.
2. Assuming that a current is present, switch off the sidelights and remove the bulb. Remove the complete bulb holder assembly from the bonnet. It is held in place with one self-tapping screw. On the upper side of the bulb holder is a small tab that holds the black plastic inner component in place. Using a small screwdriver, prise this tab up. The inner component can then be pushed out of the metal holder.
3. At the end of the black plastic component you have now exposed, you will see a small metal disc that the ' live' terminal of the bulb makes contact with. Remove this by gently releasing the grips holding it. Do this by inserting a small screwdriver into the slots in the end of the black plastic holder and opening them up slightly. BE CAREFUL THERE IS A GLASS VIAL CONTAINING MERCURY INSIDE THE BLACK PLASTIC HOLDER.
4. Place the metal disc and vial in a safe place. Looking inside the black plastic housing you will see the soldered end of the live cable. Use the tip of a small screwdriver or needle file to clean any corrosion away from this soldered end. When this is done, turn the sidelights on again and check that you have power at the end of the cable. Sidelights off. With a file or emery cloth clean both sides of the small metal disc.
5. Replace the mercury vial into the black plastic holder. N.B. The vial has a metal rod running through it. The rod has a break in it so that it appears to have a long & short end; the mercury acts as the contact between the two, allowing the light to come on only when the bonnet is raised. MAKE SURE THAT THE SHORT ROD IS AT THE WIRE END OF THE BLACK PLASTIC HOLDER. Failure to do so will result in the light being on when the bonnet is closed! Replace the metal disc making sure that the ' pimple' is uppermost and that the grips/tabs on the black plastic holder close over it.
6. Again, with sidelights on use the circuit tester to check for a current at the metal disc. You also have to hold the unit at the same angle it would be at with the bonnet open; remember the mercury tilt switch? If the test proves positive you can carry on and finish the job, if not ensure that the vial is in the right way up or clean the contacts again.
7. Assuming all is well, replace the black plastic holder back into its metal housing and push the small retaining tab back into place. Screw the unit back onto the bonnet and replace the bulb. Switch on sidelights and the light should now be working.
Of course, an alternative to the above would be to obtain a replacement unit from one of the 944 breakers that advertise in Porsche Post and change the whole thing.
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