53 Desoto Trunk Light

Paul, two things to try.

With a multimeter , test resistance from the aux switch output to the light socket. That will show whether you have a break in the wire.

Also, with your test light and ACC on, check whether you have power at other spots on the wire. ie. peirce the insulation at 6in away from the socket. maybe the socket terminals are bad.

Or maybe your headlights need to be on. My Rolls Royce trunk/hood light(s) operate this way...

Thanks Paul,

Thanks to Rick also. I had a bit of trouble posting, but that is all taken care of.

A simple trunk light, but a complex issue............

I re-wired my car, back in 1989, and never put a bulb in the trunk light. Now, I find out, the socket is live all the time. I still have the old harness, and also a parts car with the old harness intact. I will have to wait for the cold weather, to kill all the creepy crawlers in the parts car, before I start crawling around inside it myself.

In the meantime, does anyone know, what turns the trunk light on?

My Ross Roy Data Book,( for salesman) only refers to the trunk light, but does not tell how it is turned on.

Mark Waite

That's typically a mercury switch, with liquid mercury inside the body of the light that rolls to the bottom when the deck lid is up and completes the circuit between the always hot bulb socket and ground through the body.

If you have voltage to the socket terminal but the light is not lighting up, I'd make sure the socket assembly has good ground to the decklid. You should also be able to test continuity through the socket contact and the light body by rocking the assembly back and forth in a manner as if the deck lid was being opened and closed.

I dont think the key or lights have to be on. I think the circuit is supposed to be hot all the time.

When cars get restored, they often get painted in places that the manufacturer never put paint, for example between the decklid and the hinge. All that high quality paint between the panels makes for a good insulator when an electric circuit required grounding through the body panels.

Thanks Tim,

I will admit, I have not taken the socket off, and looked at carefully, but, I doubt if it has a mercury switch. It is the basic, crude, bulb socket , that when a bulb in inserted in it, it pushes the wire out the back. No other switches can be found activated by the lid itself. Did they have mercury switches back then? If I get time, this week-end, I will take it out and check for sure.

Mark

Well, maybe you caught me in an assumption.

I'm certain that the '53 Oldsmobile's trunk light and hood light were mercury switches, so the system was certainly available to the automakers.

Attached is an image of the trunk light for the '56 we're restoring. Inside is a little glass bulb (that I just learned my tech broke when he installed the new wire....grrrrrrr....) with liquid mercury in it.

Does your light look anything like that?

That is exactly what it looks like. Mine must be a mercury switch also. I was going to put a jumper on the socket, and close the lid, to see if it remained live, but, I do believe that now is uncalled for. This week-end I will take it off, and look at the "guts' of the socket, to make sure.

Thanks Tim.

Paul, if yours is not live, I wonder if the mercury switch in yours is shot?

OT, sort of, but Tim, where did you get that trunk light? Or is it the cleaned up original?

well, here's the ugly of it. (don't tell anybody)

It's original to the car. It worked when it came in. Since about 12" or so of the wire shows after it's snaked through the deck lid, we put a new wire on it and detailed the socket and bracket.

Since I checked with the tech to confirm it operated on a mercury switch for this discussion, he thought it was a good time to admit he broke the little mercury bulb while he was reinserting the socket into the bracket.

So now we've restored it, but it won't work........ until I fix something that wasn't broken to begin with........on my own time.

Oh, the secrets of the professionals........

Tim

My 53 trunk light looks the same. If the mercury switch is in there it would have to be durable since the trunk gets opened and closed and probably slammed every so often. I will be checking it out. For now there is no evidence of mercury or anything like that. I guess I do what Ben suggested to see if the switch completes the circuit to ground and then maybe take it out.Thank you all.

Since I started this trunk light thing, I will try to end it.

Last night, I took off the socket. This morning, took it to work, managed to get it apart, and.............guess what? Inside, IS a mercury switch!

When I get home tonight, I will attempt to take a photo of the switch, apart, and post it here. I would have never known......

You were right Tim.

Mark Waite

It had to happen sooner or later, Mark....

Since you have an unbroken mercury bulb, can you measure its dimensions for me so that I know what I'm looking for as a replacement?

Be careful on the reassembly!

Hi ,New guy here.
Got a 52 Firedome six weeks ago and have been working hard getting everything working,I contacted Mark about this same issue,I couldn't figure what fired the socket.Mark got back to me and said it is a mercury switch.We had thought this when we first talked but were not sure if they were using them at that time.After talking to Mark,I took the socket apart and there is a capsule inside that I got continuity through by shaking it,alot,but it still doesn't make good contact each time.The thing about this switch is that it's metal,not glass.Didn't measure it but would guess 5/8 x 1/4 in. cylinder.As I said,mines a '52.
Bart

Since the mercury switch has a metal housing maybe all I need to do is cycle it a few times. Or maybe mine has a bad connection to the negative hot side so it can not complete the circuit to the ground. Or maybe the ground is bad. I will check it out this weekend.
Mark, was the assembly easy to get apart?