Smoke coming from head light switch

[z8987]

Last night when I started the car (1970 240z #7951) I saw smoke coming from the steering column.  I went out today and opened up the column and started the car.  No smoke until I turned on the head lights.  I felt the wire heating up before it started smoking.  It's the two black wires coming out of the top of the switch.  I do have both relay harness upgrades ordered but I don't know if that's a fix for this issue.

 

Any ideas on how I can further investigate this.  I'm trying to trace the wired out to there termination point, it's kind of difficult, but I'm working on it. 

[Zed Head]

Carefully bend the four metal tabs back and the contact board will lift out of the case.  Be very careful, there are small springs and things inside.  You'll probably find pitting and maybe something melted.  If you can get things cleaned up and use relays it should be fine, with the lower current.

Be careful with the wires and solder joints.  After many heat cycles they get brittle and often crack and break off.  It's a pain resoldering them.

Looks like somebody might have been in there already.  There a threads about working on the combination switch I'll post one up if I find it.

[Zed Head]

Here's one that covers much more than the headlight switch.  Pic 37 is about the starting point.  About 2/3 down the page.

 

[Zed Head]

Here's another that shows the little pieces.  Don't lose them.

 

[jfa.series1]

The large gauge black wire on the center post is the high amperage power coming into the light switch from the fuse block, the small gauge black wire on that post is a jumper carrying power to the other side for the wiper switch. Smoke in this area says you have very high resistance either inside the switch or downstream in the wiring or at the lights. If you decide to open up the switch, I recommend you do so on a work bench topped with a soft towel. Tiny bits tend to bounce and run away on a hard surface - ask me how I know. Here's a pic of the small bits inside the switch box - rockers, tiny springs, and nylon "nubbins". You can see heavy carbon buildup on the rockers where they contact the posts on the circuit board. In the pic, one nubbin at the far right is actually melted from heat - it had to be replaced with one from a cannibalized switch.

Edited September 15, 2023 by jfa.series1

[z8987]

The large gauge black wire on the center post is the high amperage power coming into the light switch from the fuse block, the small gauge black wire on that post is a jumper carrying power to the other side for the wiper switch. Smoke in this area says you have very high resistance either inside the switch or downstream in the wiring or at the lights. If you decide to open up the switch, I recommend you do so on a work bench topped with a soft towel. Tiny bits tend to bounce and run away on a hard surface - ask me how I know. Here's a pic of the small bits inside the switch box - rockers, tiny springs, and nylon "nubbins". You can see heavy carbon buildup on the rockers where they contact the posts on the circuit board. In the pic, one nubbin at the far right is actually melted from heat - it had to be replaced with one from a cannibalized switch.

Did you clean the rockers? How about the contact points in the box, or is that the the nubbins?


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[jfa.series1]

3 minutes ago, z8987 said:

Did you clean the rockers? How about the contact points in the box, or is that the the nubbins?


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You have to clean both the rockers and the contact posts on the circuit board. The springs and nubbins just move the rockers to the various positions to make contact between the rockers and posts.

Edited September 15, 2023 by jfa.series1

[z8987]

Just received my Headlight Relay Upgrade and the parking light upgrade.  I also opened up one of the boxes on another car that has also had previous heat issues.  It's in worse shape than this one.  This car, the one I initially start this topic about has no melting or exterior signs of heating.  Do we think the resistance is cause by this box, or the heat in the box is a symptom of another problem?    I'm a little hesitant to open this box. You can see in the picture that there is a blue and white wire across the top.  It's pretty tight. Anyway, I'm going to install the relay's and get that part done. 

[jfa.series1]

There's no real telling where the issue is located. The blue/white wire across the switch is the washer circuit. You could gently move it to the side so as to open the switch. Installing the relay kit will certainly ease the power load on the switch but you still might be dealing with carboned up contacts inside and a less than optimum circuit.

[Zed Head]

You could check the switch for shorts to ground or shorts to other circuits.  If it checks out then the very small amperage of the relays probably won't bother it.  You can also check the downstream circuits for shorts also.

Which relay kits did you get?  Both the headlight circuits and the running lights can overheat.

[jfa.series1]

Here's anothe pic that might help a bit. To @Zed Head's point, the switch on the left is the same as yours, on the right is a later design. On your switch the large gauge black wire on the senter post is headlight power in and the faded red/white heavy gauge above it is headlight power out. On the left side is the parking light circuit - solid green wire in the center is power in, the green/white wire above it is power out. The unwired posts at the bottom are for the off positions of the rockers.

[w3wilkes]

After you get things put back together you should get the "Smoke replacement kit". These were initially created for Lucas wiring in British cars, but I think they'll work in ours too.

 

🤣🤣

Edited September 15, 2023 by w3wilkes