Under hood lamp

[Isaiah72]

What am I doing wrong? The under hood light wont turn on. I connected the one wire to horn relay and added a ground wire to attaching bolt. I tried turning on all the lights and still nothing???

[Canuck]

This light is controlled by a mercury switch, not by a light switch in the car. Maybe the mercury switch is not working?

[Isaiah72]

That's what I thought, I did a little research and found that the mercury swith is integrated inside the lamp I ordered another lamp and tried it but same thing. I can't imagine getting two bad lamps?

[wallaby]

I think it's your power source. I don't remember the horn relay being on the firewall.

I bet if you disconnected from that relay then extended that wire all the way to the battery you would find the light works.

 

[MCfan]

5 minutes ago, wallaby said:

I think it's your power source. I don't remember the horn relay being on the firewall.

I bet if you disconnected from that relay then extended that wire all the way to the battery you would find the light works.

 

I agree.  When I installed that same light on my '70, I connected the single power wire to a longer wire that I ran along the driver's inner fender to the horn relay on the backside of the core support, driver's side.  You could run it all the way to the battery but it doesn't draw much current so the horn relay will work.  I did not add a ground wire as attaching it to the hood with sheet metal screws served as a ground and that's the way the factory installation was on my other '70. 

Also, the factory installation has a shielded disconnect (inline plug) midway between the light and the horn relay so you can remove power from the light if you need to keep your hood up for extended period of time.  I put a similar disconnect plug inline when I added the light so I could unplug it when I was at car shows or had the hood up while working in the engine bay.  Otherwise the mercury switch will keep the light on when the hood is up.

[Canuck]

1 hour ago, wallaby said:

I think it's your power source. I don't remember the horn relay being on the firewall.

I bet if you disconnected from that relay then extended that wire all the way to the battery you would find the light works.

 

That’s the correct location of the horn relay for 72. The horn relay was moved to the firewall in 72.

[Canuck]

As Dennis mentioned above, I know in 1970 they had a fuse in line. Not sure if 72 has this but here’s a photo of that connection in my 70. If you pull it apart there’s a tiny fuse in there.