#1  
Old 09-18-2024, 12:33 PM
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Default 1970 Underhood lamps

I have a few questions regarding underhood lights in a 1970 GTO:

I found 2 mercury (positional) underhood lights in my parts box (see first 2 photos).
Both work, both look correct. One has an in-line fuse holder and a round terminal for 12V+ power. The other light has no fuse and a weird terminal.

First question: Which is correct?

A small bulb will fit as well as a larger (tail light size) bulb. Which is correct?

Next question: Where do the underhood lights receive 12V+ power? I don't know of anywhere the round terminal could attach in stock configuration, nor is there any extra connection on the stock wiring harnesses for the weird looking terminal (which I assume fits into a plastic housing of some sort).

Final question: Was a reel light an option in 1970 and, if so, is the unit pictured in photo #3 correct?

Thanks in advance for any help/info/guidance.
Jim
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  #2  
Old 09-18-2024, 02:23 PM
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Neither under hood lamp you have is correct. The A body hood light mounts to the firewall and was activated by a switch. (same as the brake light switch) 12 volt power came from the BAT terminal on the fusebox.

The reel light was available on the GP. Not sure about the GTO
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  #3  
Old 09-18-2024, 05:59 PM
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I think I have one of those in the parts box. I guess I should have checked the manuals first. Mea culpa. Thanks.
It's gonna be fun hooking up to the fusebox. This car has power windows, power door locks, power seat back release, power top, power flow through ventilation, power trunk release and hood tach, all of which hook up to the fuse box batt, ignition or acc terminals.

  #4  
Old 09-18-2024, 06:02 PM
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When did Pontiac start/stop using the mercury switch lamps? I've had two 70 GTOs that were unrestored and had the lamps in the photos above. Could it have been a late year change?

  #5  
Old 09-18-2024, 07:29 PM
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Don't know for sure but the earlier A bodies had the same set up. The switch bracket was different from the 68-70. 71-72 had a third style switch bracket but the light was still attached to the firewall.

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  #6  
Old 09-18-2024, 08:50 PM
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So where did the mercury switched lamps come from?

  #7  
Old 09-19-2024, 12:58 AM
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Chevy or Firebird? I think the one with the inline fuse is from an Olds, but don't quote me

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  #8  
Old 09-19-2024, 08:30 AM
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Big bulb or small bulb?

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Old 09-19-2024, 02:14 PM
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Should be a size '93'

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  #10  
Old 09-19-2024, 02:52 PM
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do either of these look right?
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Old 09-19-2024, 06:24 PM
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Metal switches were used through 68. and the L shaped bracket on the right was for the pre 68 A body models so that would appear to be a pre 68 switch assembly.

68-70 A body had a stepped bracket as shown below.`

Not familiar with the bracket on the left. Could be for B body?
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  #12  
Old 09-19-2024, 09:20 PM
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The design seems very inefficient. First of all why complicate matters with a separate lamp and switch when the mercury switches were in use on other GM lines and working well? On my car, a RAIV, a lamp attached to the firewall as you show would throw almost no light on anything but the rear of the Ram Air foam and air cleaner assembly. Again, the hood mounted mercury switched lamps would actually be more useful in terms of illuminating the engine bay.

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