Headlight switch problem- 1978 280z

[SteveJ]

The connector changed to a round connector. 

[Zed Head]

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.

 

Edited August 17, 2022 by Zed Head
s > x

[gotham22]

what about using some epoxy on the bad one to reform the top?  Do you think that could work?

 

[Captain Obvious]

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?

[SteveJ]

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. 

[Captain Obvious]

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

[SteveJ]

2 minutes ago, Captain Obvious said:

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

[gotham22]

Wondering if I try and find a machine shop 

[SteveJ]

10 minutes ago, gotham22 said:

Wondering if I try and find a machine shop 

What? You don't want to try casting?  

[Captain Obvious]

34 minutes ago, SteveJ said:

Yes, I'm out of my mind. Is that important?

Sorry. My bad. Who am I to say something like that!  Objection withdrawn!

[Captain Obvious]

LOL!!  

[Zed Head]

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 August 17, 2022 by Zed Head