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Headlight switch problem- 1978 280z


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I was having issues with my headlights where they would only turn on if I played with the knob and moved it back and forth in small increments. I took apart the switch and cleaned up the corrosion. One of my springs with the plastic tips that push the rockers looks melted or worn.  I am assuming this is no longer a part I can get.  Do I need the plastic piece on top of the spring or can I use the spring without it?  Is there anything I can swap the plastic piece with that could work as a fix?

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Yep, that's a problem. It melts down/wears down because of the heat from all of the current flowing through the switch. Don't try to get a 3D printed version. It will only melt down faster than the original piece.

@Captain Obvious You're better with plastics than I am. Can you think of a hard plastic that could be drilled/milled/lathed into a replacement?

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1 hour ago, SteveJ said:

 Can you think of a hard plastic that could be drilled/milled/lathed into a replacement?

Nylon 6/6 would be my first choice with Delrin being a close second. Both are easy to machine at that scale, but I think the Nylon is a little stiffer and stronger.

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1 hour ago, SteveJ said:

Don't try to get a 3D printed version. It will only melt down faster than the original piece.

What if you relay the headlights and reduce the current/heat through the switch (which is good practice anyway)?  That would presumably open up more material options.

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15 minutes ago, BoldUlysses said:

What if you relay the headlights and reduce the current/heat through the switch (which is good practice anyway)?  That would presumably open up more material options.

That's generally always a good idea.

If someone comes up with a replacement for that plastic tip, I can fix 2 or 3 headlight switches that I have.

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15 minutes ago, BoldUlysses said:

What if you relay the headlights and reduce the current/heat through the switch (which is good practice anyway)?  That would presumably open up more material options.

It's possible. The problem with most relay installations is that the owner hacks into the wiring. Now, @Captain Obvious provided me key information that would allow a relay kit to be created for the 78 that does not involve cutting any wires and could essentially be tucked away nicely. Unfortunately I don't have an unmolested 78 at my disposal to see that scheme to fruition.

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Posted (edited)

I put a single relay on my 76 to take the heat out of the switch.  If I recall right you just cut the red wire from the switch to the fuse panel and insert the relay there.  I punched a hole through the rubber plug in the firewall to the battery terminal.

Full power still runs through the dimmer switch but the combo switch only sees the amps to actuate the relay.

The circuit is kind of odd to look at because power comes through the switch from the W/R wire (on a fusible link circuit) then passes through the switch on the way to the fuse box.  So the relay doesn't control power in to the switch it controls current out.  Instead of supplying the fuse box through the switch you supply it through the relay, controlling it with the red wire out of the switch.

I have vague memories of posting (maybe just thinking) incorrect logic about the fuses in the past, I think because my thinking was backward about the current direction.  (One way in which the internet sucks.  The internet forgets nothing.).  I thought that the fuses saw less current with the relay in place.  But they see the same current just from a different source, the power still passes through the fuses on the way to the headlights.  Assuming my 2022 logic is better than that past logic.  I could be wrong.  Only adding in case someone sees an old post.  Maybe I'll dig it up myself.  (Just remembered that the fusible link is actually taken out of the circuit, not the fuses.  Rambling...)

 

p.s. if you take a few minutes and study that headlight circuit you see that there is "potential" in the factory setup to run 40 amps (assuming a green fusible link is 40 amps) through that tiny switch if there's a short in the red wire that heads to the fuse box.  Seems like the switch might melt before the fusible link.

p.s. 2 - the running lights run through the circuit right next to the headlights.  It's just a bad design.  Lots of heat.

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Edited by Zed Head
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I think epoxy or something 3D printed would both be fine for proof of concept, but I don't think they would last.

The thing that worries me about epoxy, would be low abrasion resistance and adhesion to the original remaining nub. And the thing that worries me about something 3D printed, is the very thin cross section where the nub captures the end of the spring. Brittle and prone to cracking?

And regardless of what material is used, the original part looks like it melted. So the root failure here looks like it got too hot. That needs to be taken care of first.

So since I'm in here... Other than friction resistance, is there any reason those nubs must be made out of plastic? Does it have to be non-conductive? Based on the switch pics above, it looks to me like the could be made out of metal? Brass for example?

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8 minutes ago, Captain Obvious said:

I think epoxy or something 3D printed would both be fine for proof of concept, but I don't think they would last.

The thing that worries me about epoxy, would be low abrasion resistance and adhesion to the original remaining nub. And the thing that worries me about something 3D printed, is the very thin cross section where the nub captures the end of the spring. Brittle and prone to cracking?

And regardless of what material is used, the original part looks like it melted. So the root failure here looks like it got too hot. That needs to be taken care of first.

So since I'm in here... Other than friction resistance, is there any reason those nubs must be made out of plastic? Does it have to be non-conductive? Based on the switch pics above, it looks to me like the could be made out of metal? Brass for example?

I would think that friction resistance is probably most of the reason. Also the parts supplier may have had access to injection molding equipment that would allow them to knock off a bunch of the plastic parts as opposed to machining the metal bits. (Dang it, now you have me thinking about the possibility of casting with brass. You are evil, @Captain Obvious!)

I am tempted to see about getting a 4mm delrin rod to play with to see if I could make the plastic part. 

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Casting in brass??? Pardon my French, but you're out of your mind!!  LOL  LOL!!

Unless you're going to make a hundred thousand, just turn it on a lathe! 

I could make that part in less than ten hours. Nine-and-a-half to figure out how to make it right, and then thirty minutes to make a good one.

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2 minutes ago, Captain Obvious said:

Casting in brass??? Pardon my French, but you're out of your mind!!  LOL  LOL!!

Unless you're going to make a hundred thousand, just turn it on a lathe! 

I could make that part in less than ten hours. Nine-and-a-half to figure out how to make it right, and then thirty minutes to make a good one.

Yes, I'm out of my mind. Is that important? With a lathe, there is less chance of burning something/catching something on fire. Where's the fun? Now with molten metal, opportunities abound!

Seriously, I might just buy the delrin rod.

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Posted (edited)

For a one off an Exacto knife and a pierce of plastic rod would probably do it.  It's not really a high precision piece.  Look at how long it lasted while it was melting.

p.s. if you add a relay you don't have to worry as much about the heat.  Except for the running lights right next to it.  I also ended up putting a relay on my running light circuit.  That was tougher though because Nissan buried that wire way up under the dash.  My original problem was the solder joints breaking.

Edited by Zed Head
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3 minutes ago, Zed Head said:

For a one off an Exacto knife and a pierce of plastic rod would probably do it.  It's not really a high precision piece.  Look at how long it lasted while it was melting.

p.s. if you add a relay you don't have to worry as much about the heat.  Except for the running lights right next to it.  I also ended up putting a relay on my running light circuit.  That was tougher though because Nissan buried that wire way up under the dash.  My original problem was the solder joints breaking.

Easy solution for the parking lights - LEDs all around (gauges, front markers, rear markers, and side markers)! It might even keep the connector at the steering wheel from melting.

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