Accessory Hood Light Connection

[Conn47D24]

For the purpose of connecting and under hood accessory light.

 

The instructions tell me either regulator or horn relay " hot " terminal.

 

Please guide me towards which terminal this would be on either REG OR HR.

 

Thank you in advance ?

[Sam Buchanan]

You need to add either (or both) a DC test light or a multimeter to your toolbox, many uses around our old cars. Ground one end of the light and use the probe to find the hot terminal.

 

 

https://www.harborfreight.com/612v-circuit-tester-with-5-ft-lead-63603.html?utm_source=google&utm_medium=cpc&utm_campaign=12144811130&campaignid=12144811130&utm_content=117789286078&adsetid=117789286078&product=63603&store=3256&gclid=CjwKCAjws7WkBhBFEiwAIi16870gqGlSJagQZbKOzQjTkxN6astH4vcz9SnGfNVFuse7UoZcjXoYXRoC-A4QAvD_BwE

Edited June 17, 2023 by Sam Buchanan

[SteveR]

Continuity testers are ok but I prefer to use a multi-meter. That way you can see what voltage you are getting where a continuity tester will not. You can buy Mulit-Meters cheaply. Not only that but a meter can be used in the house as well to check voltage and resistance in fuses.

 

https://www.harborfreight.com/electrical/electrician-s-tools/digital-clamp-meter-96308.html

This one will check amperage as well.

[Semmerling]

1. How does your light turn on, is there a switch onboard, is it an old mercury style movement hood style, will you need to run it to a switch?
2. Do you want it to be able to be turned on only when the key is on or anytime?

3. Does it have a cord and is moveable or is it a surface mount stationary light?

4. Is it fused?

If this is a small draw light, forget all the electrical instruments, they are not needed. Just use common sense and do not tap into anything having to do with the engine....just the running gear. If you have access back into the interior behind the dash you can properly fuse it or switch it, etc. If the light grounds when mounted and you always want to be able to turn it on at any time, well....that is a one wire run. 

 

 

All of this can impact where you tap power. 

Edited June 18, 2023 by Semmerling

[Sniper]

56 minutes ago, Semmerling said:

Just use common sense and do not tap into anything having to do with the engine....just the running gear

 

That is the OP's question.  Where does he tap into the power.  There should be a terminal labeled B on the regulator.  That's where the instructions want you to hook up.

[Conn47D24]

Thank you all.

 

I own a multimeter , understand it's basic function, but I've never mastered using it ,need to do a tutorial on YouTube I suppose. 

 

This is the old style butterfly hood style light that closes with the hood and shuts off with a Mercury switch.

Mercury, which is sketchy but I wanted to install it anyway.

 

I will attach to the "B" terminal on the regulator .

Instructions only say HOT therefore my question to be sure.

 

I'm taking here that this wiring will allow it to be used with key on or off

 

thank you !!!

[Conn47D24]

All set !

Mercury switch is spotty , but good Anyway .

[desoto1939]

Clayton:  I had one of these on my 39 Desoto and i also connected mine to the Battery Terminal on the volt regulator. Until you posted a picture of the lamp i thought you were talking about the hood ornament like onthe deSotos that had the plastic Desoto face that had a bulb behind the yellow plastic insert.

 

Just a FYI you might just want to pull the lead at the B contact point on the Volt reg when the hood is open because of the light being on. Also check the light in the dark garage when you part the car tomake sure the lights goes off and is not drawing any current to run down the battery.  Could use an alligator clip to make the quick connection when needed.

 

Car is looking great. We were at a local town car show last night that had over 300 cars and was run by the local firehouse as a fund raiser. Drove the car home around 9PM and the light were ok but not great but knew the roads so not really any big issues.  I hope to see you at Hershey in October.

 

Also happy fathers day.

 

Rich Hartung

[Conn47D24]

 

Hi Rich

 

This switch only works if I tap it a few times.

 

Also, I disconnect the battery when not driving .

 

 

Question , after I connected to B terminal,  I started the car and the Amp meter was swinging around like crazy.

Took the lead off the terminal and it still was wild.

Shut the car off disconnected the battery reconnected and it meter was back to normal sits kind of steady just a hair underneath zero as usual.

What the heck is that all about? I don't need the hood light that bad LOL

 

[Sniper]

Probably a bit of oxidation on the battery terminal. 

[Semmerling]

On 6/18/2023 at 7:03 AM, Sniper said:

 

That is the OP's question.  Where does he tap into the power.  There should be a terminal labeled B on the regulator.  That's where the instructions want you to hook up.

 Sniper, don't make a career of this.

Ok, now that we actually know what he is using and the means of turning it on, now Sniper,  we can answer his question. Me? I would bring the wire through the firewall and into a nicely prepared fuse panel and then provide a simple inside switch. Why? because the vast majority of the mercury switches I come across do not do a good job and tend to eventual fail, and do so as ON. Given that it is a mercury switch, I would allow for the means to turn it off for long term storage.  Me? I remove the mercury switch, but thats just me. 

[Sniper]

He did not ask what you would do he asked what the instructions were telling him to do. And that's the answer I gave him.

[greg g]

Why are Mercury switches spotty?  Unless the container is breached, they shouldn't be problematic.   My father used to make his own for under hood and trunk lights.  His favorite  container was those new fangled plastic medicine bottles.

Edited June 19, 2023 by greg g

[desoto1939]

21 hours ago, Conn47D24 said:

 

Hi Rich

 

This switch only works if I tap it a few times.

 

Also, I disconnect the battery when not driving .

 

 

Question , after I connected to B terminal,  I started the car and the Amp meter was swinging around like crazy.

Took the lead off the terminal and it still was wild.

Shut the car off disconnected the battery reconnected and it meter was back to normal sits kind of steady just a hair underneath zero as usual.

What the heck is that all about? I don't need the hood light that bad LOL

 

As sniper stated maybe some corrosion on the B Terminal or the connector for the light. Also might be a bare wire but the wire to the light is a covered in plastic or rubber.  Recheck the wire as it comes near the volt regulator.

 

I am stumped on this one also.

 

Rich

[Semmerling]

3 hours ago, Sniper said:

He did not ask what you would do he asked what the instructions were telling him to do. And that's the answer I gave him.

 

This is a forum and its not yours. If a person wants to ask him questions to understand his issue it might be "does it have a mercury switch" and what ever else a person might like to pleasantly ask. I gave him a link talking about my experience with mercury switches and what I did. Guess what? He has a problem with mercury switches and battery drain. One of the two of us thought that might be coming and asked. Back off or get help. 

[Dodgeb4ya]

The mercury switch itself is probably the cause of the light at times not coming on...

This as long as there is a good ground and clean 6V feed connection as already mentioned.

Old car mercury switches.. even NOS can be very troublesome.

 

Edited June 19, 2023 by Dodgeb4ya

[Sniper]

8 hours ago, Semmerling said:

Back off or get help.

 

You might want to reflect on that yourself.  Not sure why you are all wound up.

[D35 Torpedo]

Are you sure that is a mercury switch? Usually those style switches are for automatic on off function based on the angle of the fixture. Yours is hard mounted to the firewall with what looks like a plunger switch. It probably has some regular old contacts inside. I've always found mercury switches to be fairly reliable, since they are a sealed unit.

[Sam Buchanan]

The mercury switch comments had me going back for a second look at the photo. I also assumed there was a plunger activating contacts but instead the entire fixture appears to be spring-loaded and hinged so the pushrod tilts the fixture down as the hood closes. The mercury switch detects the tilt and opens the circuit. Clever!

 

Edited June 21, 2023 by Sam Buchanan

[Bob Ritter]

I have never seen a light like that, but I guess with that butterfly hood you need something like that. With all that copper piping do you have two heaters?

Sorry about the question, but I'm just trying to learn more about our cars.

[desoto1939]

Sam: is correct in his explaination of this type of underhood light. Inside the hood of the lamp is the socket and that socket is a murcury switched socket.  I had one of these on my 39 Desoto and it stopped working and also have a NOS unit still in the box. The push rod with the rubber tip makes contact with the butterfly style hood and then pushes the entire unit down and then the mercruy drops the connection for the light. When the hood opend then the mercury flows again to make the light come back on.

 

Rich Hartung

desoto1939@aol.com

[Conn47D24]

Bob,

 

Yes, dual heating units. # 53 & 54

 

Driverside unit I added, so had to do the plumbing myself. 

[D35 Torpedo]

14 hours ago, desoto1939 said:

Sam: is correct in his explaination of this type of underhood light. Inside the hood of the lamp is the socket and that socket is a murcury switched socket.  I had one of these on my 39 Desoto and it stopped working and also have a NOS unit still in the box. The push rod with the rubber tip makes contact with the butterfly style hood and then pushes the entire unit down and then the mercruy drops the connection for the light. When the hood opend then the mercury flows again to make the light come back on.

 

Rich Hartung

desoto1939@aol.com

That's pretty neat. Thanks for clearing that up. I see it now.