Underhood Light
Thread Starter
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Fleet Mechanic
Joined: May 2009
Posts: 1,460
Likes: 6
From: Bay Area, Unfortunately
Underhood Light
Hi guys,
I just finally picked up an underhood light to replace the missing one on my truck. It seems most of the ones I found in the junkyard were pure junk. I bought a seemingly good one, put it in, and it does not work. I got anywhere from 2 to 10 volts between the terminals, and I can not get the bulbs to light at any voltage (they are new). Is this common? Is this worth trying to fix? How do I fix it, and does anyone know anything more about the ball bearing switch that the EPA was offering for free?
Last question is which wire should the light plug into? I can not seem to find it under the hood and I can not find it in any schematic.
I just finally picked up an underhood light to replace the missing one on my truck. It seems most of the ones I found in the junkyard were pure junk. I bought a seemingly good one, put it in, and it does not work. I got anywhere from 2 to 10 volts between the terminals, and I can not get the bulbs to light at any voltage (they are new). Is this common? Is this worth trying to fix? How do I fix it, and does anyone know anything more about the ball bearing switch that the EPA was offering for free?
Last question is which wire should the light plug into? I can not seem to find it under the hood and I can not find it in any schematic.
Senior User
Joined: Aug 2008
Posts: 132
Likes: 1
It may not help you at all but I did the exact same thing, bought a junkyard light and attached it to my hood.It was a green wire with a yellow stripe that came out of the harness near the brake booster. It also helped that this wire was running along my hood already but...
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
The Underhood lamp was an Option.
It did not come on the trucks standard.
The lamp has a seperate harness extention that runs under the hood to the plug next to the brake booster. Light Green/Yellow Stripe wire.
The Ground hooks to the Hood.
You also need to have the hood to Firewall ground strap. If you don't have this strap, the light won't work.
It did not come on the trucks standard.
The lamp has a seperate harness extention that runs under the hood to the plug next to the brake booster. Light Green/Yellow Stripe wire.
The Ground hooks to the Hood.
You also need to have the hood to Firewall ground strap. If you don't have this strap, the light won't work.
Thread Starter
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Fleet Mechanic
Joined: May 2009
Posts: 1,460
Likes: 6
From: Bay Area, Unfortunately
Thanks, I have the strap, the wire leading to the light, and I put it into a switched source for now, because I could not find the plug next to the booster. Is there any way to clean it for the contacts, or is this a sign of the mercury switch going? Should I even try to fix it?
Thanks
Thanks
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
You can split it apart by drilling the rivets.
This way you can also replace or change the mercury switch as well.
To put it back together, use rivets or small nuts and bolts you can get at the hardware store.
Just becareful of the spring and lamp cord pulley when you take it apart.
This way you can also replace or change the mercury switch as well.
To put it back together, use rivets or small nuts and bolts you can get at the hardware store.
Just becareful of the spring and lamp cord pulley when you take it apart.
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
Do a search online. In some cases you can get a free ball bearing replacement for the mercury switch.
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Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
A toggle switch works fine. Plus they are $2 at the local ace.
You dont need a ground strap either. Mine is missing and my light runs fine.
You dont need a ground strap either. Mine is missing and my light runs fine.
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Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
A Free ballbearing switch is better that $2, and it would work as original, and wouldn't be cheezy in my opinion.
Then how does your lamp complete the circut? It has to ground somewhere.
Light grounds to hood. Hood Grounds to firewall. The hood will not be grounded properly just going through the hinges. The hinges pivot and are a loose connection. It needs the Factory Ground strap.
You dont need a ground strap either. Mine is missing and my light runs fine.
Light grounds to hood. Hood Grounds to firewall. The hood will not be grounded properly just going through the hinges. The hinges pivot and are a loose connection. It needs the Factory Ground strap.
Tuned
Joined: Oct 2006
Posts: 361
Likes: 0
From: Eagle River, Alaska
With out removal, you may try extending the lamp several times to gain better contact between the extension and the case. Years of non-use could result in poor internal contacts that would act like a bad internal switch. I noticed with my unit though that the extending wire had been retracted in a twist next to the bulb that had become rather tight. Manipulation of the lamp in this state can cause severing of the wire internally. A volt meter used while moving the separate contact (extension, wire) may narrow the problem to the point of origin. best wishes.
FTE Leadership Emeritus
Joined: Sep 2000
Posts: 7,298
Likes: 45
From: Southern California
Great thread! Rep for all. My '81 F250 has an underhood light that works every time. My newer vehicles have had trouble with the bulbs or did not have it at all. You guys are the best and ford rocks.
Thread Starter
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Fleet Mechanic
Joined: May 2009
Posts: 1,460
Likes: 6
From: Bay Area, Unfortunately
I really agree! Thank you guys for all the help...Something as menial as an underhood light has garnered a lot of response and help! I am still tinkering with this and am getting to the root of it - I hope.
Postmaster
Joined: Feb 2008
Posts: 2,658
Likes: 5
From: Out of here
I would not do the "toggle switch" mod if I were you.
The purpose for the mercury switch was to ensure that the light would only come on with the hood raised.
If you "re-engineer" it by using a toggle switch, there is a chance that you could forget to turn it off, or accidentally turn it on during the day without knowing and kill your battery.
I am always a firm believer in keeping things stock unless there is a BETTER way to do it then they did from the factory. In this case, I think the factory did it right (sans the mercury).
The purpose for the mercury switch was to ensure that the light would only come on with the hood raised.
If you "re-engineer" it by using a toggle switch, there is a chance that you could forget to turn it off, or accidentally turn it on during the day without knowing and kill your battery.
I am always a firm believer in keeping things stock unless there is a BETTER way to do it then they did from the factory. In this case, I think the factory did it right (sans the mercury).
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
Used a toggle switch on my 96 XL. Worked fine. never had a problom remembering to turn out the switch. Everytime I forgot the glow under the truck gave it away.
The circuit will ground through the hinge. Try it. Please, please, dont argue worthless info.
The circuit will ground through the hinge. Try it. Please, please, dont argue worthless info.
Postmaster
Joined: Feb 2008
Posts: 2,658
Likes: 5
From: Out of here
My point still stands and I'm not "arguing worthless info".
Why would you want to "rig" something up like that when you can easily fix it so that it functions the way it should?
I personally am here to try and set an example of fixing things right, not half-baked.
Once again: the reason FORD did it like that in the first place is so that you don't forget to turn it off, and it will only turn on when the hood is up. Right when you need it.
You could easily turn the switch on during the day (either purposely or accidentally) walk away from the vehicle for a few days and kill your battery. When the mercury switch is functioning properly the light works as designed, and you NEVER have to worry about leaving it on unintentionally.
Why do you think they have automatic shutoffs on headlights these days? Don't tell me you have never left your lights on and came back to a dead vehicle.
Same principle.
Why would you want to "rig" something up like that when you can easily fix it so that it functions the way it should?
I personally am here to try and set an example of fixing things right, not half-baked.
Once again: the reason FORD did it like that in the first place is so that you don't forget to turn it off, and it will only turn on when the hood is up. Right when you need it.
You could easily turn the switch on during the day (either purposely or accidentally) walk away from the vehicle for a few days and kill your battery. When the mercury switch is functioning properly the light works as designed, and you NEVER have to worry about leaving it on unintentionally.
Why do you think they have automatic shutoffs on headlights these days? Don't tell me you have never left your lights on and came back to a dead vehicle.
Same principle.