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Fixed my underhood lights

Old 03-13-2017, 10:40 PM
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belairbrian
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Default Fixed my underhood lights

When I bought the car the lights weren't working. It wasn't a priority to fix, but last night I had some spare time so i figured I'd look into it.

Driver's side was easy, it was mounted upside down so the mercury switch never closed.

passenger's side was a little more complicated. I had 12v across the terminals with the bulb out. Took the bulb to the bench power supply and it worked. Installed an LED version of the bulb and it barely turned on.

So I had voltage but not sufficient current. Cleaned the bulb holder and mercury switch with no improvement.

Went to the connector on the right corner/turn light assembly.
Separated it and inserted 12v directly to the bulb side and it started working. Looked in the supply side of the connector and found oxidation.

Pulled the fuse and cleaned the connector with contact cleaner and some dental pick scraping. That cured the problem.

hope this helps someone else.

Last edited by belairbrian; 03-13-2017 at 10:41 PM.
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Old 03-14-2017, 02:19 AM
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GREGGPENN
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So, the underhood courtesy light get power from the turn-light assembly? Interesting that it would have power all the time. I get what you are saying about the plug/connector though.

More importantly, how did you clean the mercury switch? I always felt that was the problem on my passenger side light.

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Old 03-14-2017, 08:03 AM
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Originally Posted by GREGGPENN View Post
So, the underhood courtesy light get power from the turn-light assembly? Interesting that it would have power all the time. I get what you are saying about the plug/connector though.

More importantly, how did you clean the mercury switch? I always felt that was the problem on my passenger side light.

The power comes from a fuse mounted to the left turn lamp assembly. It's closed in a cover. I'll post up a pic tonite. From the fuse it goes to a two pin connector on each side of the car. Also on the turn lamp assembly.

As far as cleaning the switch, They just pop out with the use of a small screw driver. Mine had a white/grey oxidation which i cleaned of with cleaner and a brass brush around the outside and on the tip. As I mentioned the corrosion that I had trouble from was in the two pin connector for the passenger side.

One other thought, if your spraying contact cleaner make sure you have the fuse out our you could create a short circuit and blow the fuse.

BTW i'm pretty sure it's the same mercury switch that is in the center console.
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Old 03-14-2017, 10:30 AM
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Went to LED's about a year ago. Great for showing the engine bay at night. Probaly 2 to 3 times the brightness.

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Old 03-14-2017, 10:44 AM
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Nice write up. I worked for AMP/Tyco Electronics for 30+ years in the connector divisions. It's easy to forget about the maintenance of the connectors. Especially the ones in the front of the car. These connections are getting old and need maintenance. The corrosion creates resistance and that creates problems. Dielectric grease is your friend.....just clean contacts gently, you want to remove as little finish as possible.
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Old 03-14-2017, 03:54 PM
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Originally Posted by belairbrian View Post
The power comes from a fuse mounted to the left turn lamp assembly. It's closed in a cover. I'll post up a pic tonite. From the fuse it goes to a two pin connector on each side of the car. Also on the turn lamp assembly.

As far as cleaning the switch, They just pop out with the use of a small screw driver. Mine had a white/grey oxidation which i cleaned of with cleaner and a brass brush around the outside and on the tip. As I mentioned the corrosion that I had trouble from was in the two pin connector for the passenger side.

One other thought, if your spraying contact cleaner make sure you have the fuse out our you could create a short circuit and blow the fuse.

BTW i'm pretty sure it's the same mercury switch that is in the center console.

I picture a mercury switch as a reservoir filled with liquid mercury. And, to clean THAT, you'd have to disassemble, pour/save the mercury, clean, and reassemble.

Since you didn't mention anything along those lines, it sounds like you didn't pull the lights physically apart?

Or...do I have a misconception of a mercury switch?
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Old 03-14-2017, 07:27 PM
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Originally Posted by belairbrian View Post
Driver's side was easy, it was mounted upside down so the mercury switch never closed.
Originally Posted by scuba717 View Post
It's easy to forget about the maintenance of the connectors. Especially the ones in the front of the car. These connections are getting old and need maintenance.

Thanks, these are both good suggestions. I need to get busy and fix my passenger side light now
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Old 03-14-2017, 07:55 PM
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The fuse is in this holder - should be 10 amp
the connector is for the drivers side the passengers is in the same place (on the other side obviously)


The mercury switch is in the top of the light assy (unless some moron installed the light upside down)


this is the mercury switch removed and cleaned. it pops in and out fairly easily


this is the end of the switch showing the contact and insulator
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Old 03-14-2017, 07:58 PM
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Originally Posted by GREGGPENN View Post
I picture a mercury switch as a reservoir filled with liquid mercury. And, to clean THAT, you'd have to disassemble, pour/save the mercury, clean, and reassemble.

Since you didn't mention anything along those lines, it sounds like you didn't pull the lights physically apart?

Or...do I have a misconception of a mercury switch?
I added some pics to make this clearer. I took the switch out and cleaned it up. It had a fair amount of oxidation (a white film) that I brushed off both on the body of the switch and the center contact.

The switch is sealed and being shield should not have corrosion on the inside.
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Old 03-14-2017, 08:01 PM
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Originally Posted by CREWZIN View Post
Went to LED's about a year ago. Great for showing the engine bay at night. Probaly 2 to 3 times the brightness.

I've gone to LEDs on the hood lights, B-pillar lights, door lights, mirror lights and floor lights.
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Old 03-16-2017, 10:16 AM
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Originally Posted by belairbrian View Post
I've gone to LEDs on the hood lights, B-pillar lights, door lights, mirror lights and floor lights.
Did you have to change anything other than just the bulbs?
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Old 03-16-2017, 10:23 AM
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This is awesome... It's one of the only things wrong with my vette...
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Old 03-16-2017, 11:40 AM
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Absolutely going to look into this, as mine are INOP as well...and I hate dealing with electric crap...Just a PITA honestly

D.
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Old 03-16-2017, 04:44 PM
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Originally Posted by FOURSPEEDVETTE View Post
Did you have to change anything other than just the bulbs?
For what I've changed it was just bulbs. Once you get into turns is where it gets complicated.

One thing I found was with the map lights in the mirror. You have to choose if you want them to work with the other lights OR independently. Can't have both like with the incandescent bulbs. Also to install the LEDs in the mirror I had to remove the lenses. i couldn't get them in from the back like the original bulbs.
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Old 03-16-2017, 04:46 PM
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Originally Posted by Need A Vette View Post
Absolutely going to look into this, as mine are INOP as well...and I hate dealing with electric crap...Just a PITA honestly

D.
I fixed aircraft electronics for 20 years so light circuits are pretty basic to me. This circuit is pretty basic and doesn't really need a meter to troubleshoot. It can be done with a test light.
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Old 03-22-2017, 02:34 PM
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Great write up - Thank you!

Two quick questions:

1) So the fuses are located on either side of the car, in the nose of car and not where all the typical fuses are? Also - what is used to get that out? A little flat head?

2) The mercury switch needs to be removed and cleaned? Im assuming this can be done with a steel brush or brass brush?

Thanks again!
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Old 03-22-2017, 04:47 PM
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Originally Posted by Mayor111 View Post
Great write up - Thank you!

Two quick questions:

1) So the fuses are located on either side of the car, in the nose of car and not where all the typical fuses are?Thanks again!
Only one fuse on the drivers side, so if the one fuse blows both lights go out and yes the fuse is down by the signal assembly rather than a fuse box

Originally Posted by Mayor111 View Post
Also - what is used to get that out? A little flat head?
The fuse holder has a cover with retainers like most of the connectors you can lift it with your finger and open it. There is a picture of it open




Originally Posted by Mayor111 View Post
2) The mercury switch needs to be removed and cleaned? Im assuming this can be done with a steel brush or brass brush?
I popped mine out an used a brass brush. They pop in and out like an old glass type fuse. In the end it was cleaning a dirty connector behind the passengers side turn assy that got my passenger side working
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Old 03-22-2017, 04:57 PM
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I wonder if mine work. I've had them unhooked for 15+ years
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Old 03-22-2017, 05:03 PM
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BOOM!! Bro - Thank you!! Opened the fuse, and sure enough, the fuse was broken/bad inside.

My under-hood lights lit up like Christmas trees once I swapped out the fuse!!

I owe ya one!
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Old 03-22-2017, 08:52 PM
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I've never really looked at mine or had them out to see how that mercury switch worked, but you said one didn't work because it was upside down. Makes me wonder then if it could come on when the hood is down instead of up and be the mystery battery drain some people sometimes get.
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