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Topic: Underhood Light - 78 C3

in Forum: C3 Electrical


Underhood Light - 78 C3

Posted: 1/14/23 4:17pm Message 1 of 11
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The Villages, FL - USA
Joined: 8/14/2012
Posts: 40
Vette(s): 78 Black Coupe with Oyster interior and mirrored T tops

My underhood light had not worked since I bought the car several years ago (it was pretty rusty among other things). So today I put in a new assembly, which I've had for a few weeks. It was straight forward and I was able to swap it out to the harness connection the other one was connected too. I had assumed a toggle switch  on the passenger side firewall was the trip switch...lift up the hood it would go on and had been disconnected since I owned the car. Anyway I put in the light bulb and pop the light comes on! Now I'm confused since I didn't connect that toggle switch. I like to know where the right switch is, cause all I have to do is close the hood and the light goes out. Or open the hood and as I lock it in the open position the light comes on. I cannot find a switch that the hood or struts might be connected. I'm concerned as I would prefer to be able to keep the light off while I'm showing the car. I know I can disconnect the bulb or the connection at the harness but I guess I'm a perfectionist and want to know how this sucker is working.

I have the huge trouble shooting wiring book for the 78 vette and I cannot find the underhood light mentioned in the drawings. I'd also like to know what that other toggle switch is for as everything else seems to work on the car, except the AC.

Anyone have an idea on either? Thanks

Late edit: the toggle switch is not toggle, but a plunger type of switch. Sorry for any confusion. 



|UPDATED|1/14/2023 4:17:06 PM (AZT)|/UPDATED|



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Re: Underhood Light - 78 C3

Posted: 1/14/23 4:09pm Message 2 of 11
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 916
Vette(s): 1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day. 2023 Accelerate Yellow HTC Stingray

I believe the underhood lite uses a mercury switch to activate it.  Is the toggle switch that you mentioned OEM or aftermarket?  It might be an ignition kill switch if it's not easily spotted.  Otherwise you'll need to track the wiring down.




1973 L-82 4 spd

Re: Underhood Light - 78 C3

Posted: 1/14/23 4:14pm Message 3 of 11
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The Villages, FL - USA
Joined: 8/14/2012
Posts: 40
Vette(s): 78 Black Coupe with Oyster interior and mirrored T tops

That makes some sense, because I can rock the hood and the light will flicker on and off. Would love to know where it's at though. The other switch is actually a plunger switch (not toggle...my bad). It's standard because I see it in manual pictures, but as background. Thanks!




Re: Underhood Light - 78 C3

Posted: 1/14/23 4:33pm Message 4 of 11
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The Villages, FL - USA
Joined: 8/14/2012
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Vette(s): 78 Black Coupe with Oyster interior and mirrored T tops

I did find the switch/light for the hood in my book, don't know if it's helpful, I'm not a trained electrician.




Re: Underhood Light - 78 C3

Posted: 1/14/23 4:43pm Message 5 of 11
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 916
Vette(s): 1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day. 2023 Accelerate Yellow HTC Stingray

That's the mercury switch inside the lite housing.




1973 L-82 4 spd

Re: Underhood Light - 78 C3

Posted: 1/14/23 5:53pm Message 6 of 11
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Grapevine, TX - USA
Joined: 8/26/2006
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Vette(s): 1972 LT-1 convertible with factory air. 2017 Black Rose Grand Sport convertible.

The plunger switch you found is probably for the alarm.




   

Re: Underhood Light - 78 C3

Posted: 1/14/23 7:52pm Message 7 of 11
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The Villages, FL - USA
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Vette(s): 78 Black Coupe with Oyster interior and mirrored T tops

@73shark - If it is, it's the smallest switch ever. There's just doesn't seem enough room with the size of the unit holding the socket for the light. But that seems to be a possiblity for sure. I still have the old one, think it'll take it apart, if possible. Thanks

 



|UPDATED|1/14/2023 7:52:27 PM (AZT)|/UPDATED|



Re: Underhood Light - 78 C3

Posted: 1/14/23 7:54pm Message 8 of 11
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The Villages, FL - USA
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Vette(s): 78 Black Coupe with Oyster interior and mirrored T tops

@F4Gary - could be, I'll try opening the hood with the alarm on. I know the alarm works with the doors, so we'll see. Thanks.

 




Re: Underhood Light - 78 C3

Posted: 1/14/23 8:26pm Message 9 of 11
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 916
Vette(s): 1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day. 2023 Accelerate Yellow HTC Stingray
Custommilt said:

@73shark - If it is, it's the smallest switch ever. There's just doesn't seem enough room with the size of the unit holding the socket for the light. But that seems to be a possiblity for sure. I still have the old one, think it'll take it apart, if possible. Thanks

 

A mercury switch can just be a tiny capsule w/ two electrodes on one end.  When the capsule is tilted so the mercury touches both contacts, it completes the circuit as mercury is a metal and conducts electricity. Often called a tilt switch like TV bombs that go off when the package is picked up or moved.
 
Let us know what you turn up in your analysis of the old one.







1973 L-82 4 spd

Re: Underhood Light - 78 C3

Posted: 1/15/23 5:00pm Message 10 of 11
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The Villages, FL - USA
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Vette(s): 78 Black Coupe with Oyster interior and mirrored T tops

@73Shark - you nailed it. I went back to the vendor site and in the description, besides the wire etc it included the mercury switch. Many thanks!  I've yet to test out the other switch. But thanks again. 




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