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Discussion Starter #1 (Edited)
This is a stupid, piddly question, but it's been driving me nuts! How does the light under the hood come on? Is there a pressure switch somewhere (like in a refrigerator)? My light hasn't worked in some time but the bulb is good - and, if I have the hood open when I are/disarm my car alarm, it flashes just like all the other lights do. So what in the world makes it turn on when you open the hood? I've looked all around the hood/engine area, traced the wire from the bulb as far as I could (not far, it goes into a bundle), and I've scoured my Deville Service Manual, I can't find a thing!
 

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Turn your parking lights on with the hood up. It's controlled by a mercury switch in the bulb socket, which is wired into the parking light wire. Why Cadillac did this, we will never know.
 

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DaveSmed said:
Turn your parking lights on with the hood up. It's controlled by a mercury switch in the bulb socket, which is wired into the parking light wire. Why Cadillac did this, we will never know.
Oh Good Lord! You're absolutely right! This has been driving me crazy for years! I KNEW I'd seen the under-hood light on before long ago - and it must have been at night when I had the other lights on! Here I've changed that bulb and searched and searched for a pressure switch. Why Cadillac has it this way IS a good question. So if you happen to be working on your car at night and need some light, you're supposed to leave the parking lights on and run down the battery, is that it? Hmm. And with your answer, I WAS able to find it in my Deville Service Manual under the Electrical Diagnosis/Interior Lights/Engine Compartment/Ashtray wiring diagram. How obscure! Again, Good Lord! However, it does say the light is off when the hood is closed so the mystery still remains of how the system knows whether the hood is open or not!
 

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The lamp itself still has a Mercury switch. There are other GM cars that have a lamp that operates this way. That way, when you're working under the hood during the day, the lamp isn't burning. My Allante doesn't work that way. Lights on or off, the underhood lamp comes on when you pop the hood. It's a PITA, so I pop the fuse to keep it off until I'm done working.
 
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