Ignition switch wiring issue: make it make sense

[Hydro626]

I've got a 72 Super that I've been driving for about 15 years now. Recently I noticed some of the wires behind the ignition switch got pretty hot sometimes. I figured out that they only get hot when the headlights are on. I have no idea how long they've been doing this.

Looking at the back of the switch I see where I rigged the system 15 years ago by tying the headlight (black/yellow) wire to the ignition (black) wire and sticking them both on terminal 15. "I should probably fix that" I thought to myself, and so I split the two wires up with new connectors and plugged them into their correct terminals: 15 for the black and X for the yellow/black.

Aaaaand the car won't start. The headlights come on with the key on but the car won't start. Confused, I tied the wires back together and the car starts right up.

What on EARTH is going on? Isn't the black/yellow wire supposed to deliver power TO the headlights? How could the ignition wire be getting power from it? Or is it getting a ground through that wire? Can I leave them tied together like they've been for over a decade now and not cause any problems?
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1972 Volkswagen baja Super Beetle "Elizabeth"
1989 Cadillac Brougham D'elegance

"Never name your car...too much unhealthy emotional connection coupled with your human dark/light,yin/yang energy affects the mechanical health of the vehicle and causes magnetic convergences like the one you just had.that, or some old f**k backed into your car,its hard to tell..." -johnnypan

[airschooled]

It sounds like the 15 portion of your switch went out, and you supplied 12v to the ignition circuit through the X (headlight/wiper) output on the switch. Since the X terminal was doing double duty, I'd replace your ignition switch now with one that hasn't been heat-warped.

Robbie
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[Hydro626]

[ashman40]

Power comes into the ignition switch over the solid red #30 wire. This is battery constant 12v+.
Inside the ignition switch, the key in the ON/RUN position will power both #15 (black wire) and #X (black/yellow wire) from #30. When you turn the key to START power is cut from the #X terminal while #15 and #50 (red/black wire) which powers the starter solenoid are powered. By powering both of these wires the engine will crank and the ignition will spark the spark plugs. The #X wire which powers the wipers, headlights and blower is not powered while the starter is cranking.


Separate your merged wires and test your ignition switch wires.

#30 (red) = constant 12v+
#15 (black) = 12v while key is in ON/RUN and START
#50 (red/black) = 12v only while key is in START
#X (black/yellow) = 12v only while key is in ON/RUN position

Using the above test, confirm whether it is the #15 or #X output of your ignition switch which had failed?


If your ignition swith #15 is working and #X is not, you can continue to use your ignition switch but I would recommend adding a cheap 30A SPST relay on the #15 wire between the ignition switch and the fuse box. The output of the relay can power BOTH the #15 and #X wires. The only difference with this arrangement is your headlights and wipers will continue to work while your crank the engine. As long as you have a strong battery you are good.

Otherwise, if either #15 or #X output is not working you could replace your ignition switch with a new one. I would still suggest adding the relay on the #15 wire as a way to extend the life of your new (Chinese made) igniton switch. You should also add a Hard Start Relay on the #50 wire under the rear seat. Also to extend the life of your new ignition switch. The relays reduce the current load on the internal contacts of the ignition switch so they can last decades. Without the relays the internal contacts can burn and become unreliable after only a few months/years.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Hydro626]

[Hydro626]

Just went out and tested the ignition switch with a test light. Everything checked out. 12v at every point where it should be and nowhere where it shouldn't be. I genuinely don't know why separating the black wire and the yellow/black wire made the car not start. Unless that was a bad spade connector on the black wire somehow ¯\_(ツ)_/¯
_________________
1972 Volkswagen baja Super Beetle "Elizabeth"
1989 Cadillac Brougham D'elegance

"Never name your car...too much unhealthy emotional connection coupled with your human dark/light,yin/yang energy affects the mechanical health of the vehicle and causes magnetic convergences like the one you just had.that, or some old f**k backed into your car,its hard to tell..." -johnnypan

[kreemoweet]

So the defect in your ignition circuit must be downstream from the ignition switch. According to the stock wiring diagram, the black wire from term 15 on the ignition switch goes to the supply side of #11 fuse, which is connected internally to the supply side of #12 fuse, which is connected by black wire to the ignition coil term. #15. The headlight switch is not involved in any way in that circuit.
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'68 bug: seized by the authorities
'71 kombi: not yet seized by the authorities

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[Hydro626]

[ashman40]

Good job troubleshooting!

_________________
AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}