Underhood light operation?
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 2,096
Likes: 15
Underhood light operation?
I just replaced my underhood light assembly with harness because it didn't work and the wires were brittle. But now with the new one in place and plugged in it still don't work. Is there a trick? I tried turning the rheostat for interior lights thinking maybe that was it but it wasn't. Now that I'm writing this I'm wondering if the headlights have to be on??? Hmmm. Gonna go check
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
Light on my '77 comes on anytime hood is raised. No need to have anything else turned on. Use a volt meter to see if you have a constant 12v to the wire coming from the wiring harness to the light. You must also have a ground wire going to the hood prop. Here are pics. of mine. mike...
Last edited by mds3013; Oct 5, 2012 at 09:55 AM.
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 2,096
Likes: 15
Light on my '77 comes on anytime hood is raised. No need to have anything else turned on. Use a volt meter to see if you have a constant 12v to the wire coming from the wiring harness to the light. You must also have a ground wire going to the hood prop. Here are pics. of mine. mike...
Racer
Joined: May 2008
Posts: 327
Likes: 2
From: Livermore California
there is a switch near the windshield next to the hood latch on the drivers side. it is hot all the time. when you close the hood, the light goes out (a la refrigertator), raise hood ... light on.
Safety Car
Joined: Jun 2004
Posts: 4,360
Likes: 221
From: Beecher Illinois
That plunger switch by the firewall has nothing to do with the underhood light. That's for the alarm system.
There is a mercury switch capsule inside the light housing. Mercury fluid turns it on and off depending on angle of the light.
Open the housing and you'll see the little capsule.
The light connects to the big red wire that goes to the alternator. There should be a fused link in the light harness.
I believe 80-82 lights used two wires going all the way under the hood, hot and ground, rather than the ground tied into the hood support like earlier years.
There is a mercury switch capsule inside the light housing. Mercury fluid turns it on and off depending on angle of the light.
Open the housing and you'll see the little capsule.
The light connects to the big red wire that goes to the alternator. There should be a fused link in the light harness.
I believe 80-82 lights used two wires going all the way under the hood, hot and ground, rather than the ground tied into the hood support like earlier years.
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Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 2,096
Likes: 15
That plunger switch by the firewall has nothing to do with the underhood light. That's for the alarm system.
There is a mercury switch capsule inside the light housing. Mercury fluid turns it on and off depending on angle of the light.
Open the housing and you'll see the little capsule.
The light connects to the big red wire that goes to the alternator. There should be a fused link in the light harness.
I believe 80-82 lights used two wires going all the way under the hood, hot and ground, rather than the ground tied into the hood support like earlier years.
There is a mercury switch capsule inside the light housing. Mercury fluid turns it on and off depending on angle of the light.
Open the housing and you'll see the little capsule.
The light connects to the big red wire that goes to the alternator. There should be a fused link in the light harness.
I believe 80-82 lights used two wires going all the way under the hood, hot and ground, rather than the ground tied into the hood support like earlier years.
Safety Car
Joined: Jun 2004
Posts: 4,360
Likes: 221
From: Beecher Illinois
Can you test your old light on the bench with a battery?
Maybe you have a bad connection in the harness. Can you find the end of the wire that comes out of the harness? Do you have a test light you can use at that connector?
Maybe take a jumper wire to the stud/red wire on the back of the alternator to the pos side of the light connector as a test.
Maybe the ground is bad. Bulb good?
The light basically ties into that red wire at the alternator, just with the connection buried in the harness by the inner fender.
NOTHING else needs to be turned on for the hood light to work. It's wired directly to hot.
Maybe you have a bad connection in the harness. Can you find the end of the wire that comes out of the harness? Do you have a test light you can use at that connector?
Maybe take a jumper wire to the stud/red wire on the back of the alternator to the pos side of the light connector as a test.
Maybe the ground is bad. Bulb good?
The light basically ties into that red wire at the alternator, just with the connection buried in the harness by the inner fender.
NOTHING else needs to be turned on for the hood light to work. It's wired directly to hot.
Thread Starter
Melting Slicks
Joined: Jun 2011
Posts: 2,096
Likes: 15
Can you test your old light on the bench with a battery?
Maybe you have a bad connection in the harness. Can you find the end of the wire that comes out of the harness? Do you have a test light you can use at that connector?
Maybe take a jumper wire to the stud/red wire on the back of the alternator to the pos side of the light connector as a test.
Maybe the ground is bad. Bulb good?
The light basically ties into that red wire at the alternator, just with the connection buried in the harness by the inner fender.
NOTHING else needs to be turned on for the hood light to work. It's wired directly to hot.
Maybe you have a bad connection in the harness. Can you find the end of the wire that comes out of the harness? Do you have a test light you can use at that connector?
Maybe take a jumper wire to the stud/red wire on the back of the alternator to the pos side of the light connector as a test.
Maybe the ground is bad. Bulb good?
The light basically ties into that red wire at the alternator, just with the connection buried in the harness by the inner fender.
NOTHING else needs to be turned on for the hood light to work. It's wired directly to hot.
