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Old 29-07-2020   #1
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Ignition Switch Problem

I.have a 1974 124 Spider. I did the “brown wire modification” in order to correct a starting problem. Please note that I am an electrical idiot. Followed the instructions and then tried to start the car. Cranked over fine but had smoke coming from the ignition switch on the third try. Assumed I did something wrong and burned out the ignition switch. Ordered a new switch and replaced along with all fuses under left side of the dash. I have nothing when I turn the switch. There is what looks like to me another fuse holder (longer, black ends) that connects to one of the wires going to the ignition switch but I have not opened it, etc. I did not reinstall the switch into the columns while testing but do not know if that could cause a problem. Any help/advice greatly appreciated! As I said earlier, I am electrically challenged and classic Fiat mechanics are pretty rare in Easley, SC! Thanks
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Old 1 Week Ago   #2
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Re: Ignition Switch Problem

Did you ever sort out the problem? Nearly any mechanic who can troubleshoot electrical problems should be able to help. If you really don't know anything about electronics and don't want to, I'd suggest finding a mechanic. If, on the other hand, you want to learn a bit...

I just worked on my ignition switch (1978 124 Spider). You should have a 12V tester of some sort. You can buy a cheap one (such as this: https://www.amazon.com/JASTIND-Autom...2FT/ref=sr_1_5) or find a similar item at a local car parts store. The basic idea of that part is you touch part of it to ground (nearly any unpainted metal in the car, such as a nut or screw) and then you can touch the tip to various wires to see if you have voltage. Cars operate on 12V. If you touch a 12V live wire, the probe lights up. Note this is not a dangerous amount of power, but you could possibly damage some parts if you did the wrong thing (though more likely you'd just blow a fuse)

With a voltage tester in hand (I actually used a multimeter but the result is the same), what I did was to connect to ground (the car frame, which is connected to the negative terminal of your car battery) and then I carefully stuck the positive probe into the back of the white molex connector that comes off the ignition switch pigtail of wires. The brown wire should always have power, if the battery is connected. I confirmed that, then I confirmed that none of the other wires had power.

Next, you turn the key to the "on" position. At this point, you should be able to see 12V on all of the wires coming out of the switch except one (in my car, the red one). That red wire goes to the starter, the other wires power up things like your radio, horn, lights, etc.

If you have power coming out of the ignition switch, but not at all the accessories, then the very likely issue is something at your fuse block. Maybe you put in the wrong size fuse and they popped? Maybe you touched another fuse and broke it? I found the fuse block to be very finicky on my car, so I actually just replaced it as described here: https://www.mirafiori.com/faq/conten...Ofuseblock.htm. That might be ambitious for someone who's afraid of electronics, but if you own a Fiat, you might need to level up on your mechanic skills. :-)

Anyway, if you still need help, respond here, I'll see what I can do. Sadly this forum seems to have a lot of unanswered posts. I'm not anything close to a mechanic, but I can get by under the hood and I'm decent enough with electrical systems.
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