Ignition switch problems!

[Yelcamino]

Hey guys,

I need some suggestions asap if possible! The other day I came home from work in my 71 Blazer, turned the key to off and the engine kept running like I didn’t do anything. https://static1.pt-content.com/images/noimg.gif

So, being the smart guy that I am, I went to NAPA and bought a new ignition switch. I installed it a few minutes ago, started the engine, let it run for a minute or two and then turned the key to off, and guess what? It kept running! Obviously the ignition switch isn’t the problem. https://static1.pt-content.com/images/noimg.gif I guess I’m not so smart any more!

Has anyone had this happen before and if so, what did you do to fix it? This is my daily driver so I need to figure this one out quickly! Thanks.

[Jim Nilsen]

I have heard that this happens when one of the diodes goes bad in the alternator. Get your alternator checked to find out if it is working correctly.
This is just something I have heard of and have never had the problem myself.

[Madspeed]

Yup what Jim said is correct
that can do it unplug it and retry youll know pretty quick.
I own a 72 4X4 blazer since 1975 (well passed down to me From Pops)

[Yelcamino]

I think I fixed the Blazer. To rule out the alternator, I disconnected all the wires from it, started the engine and then turned the key off with no luck, the engine kept running. So now, with my trusty $5 multi-meter in hand I decided to check voltage since the alternator wasn't the culprit.

The first place I checked my voltage was at the fuse box and this is where I found the problem. There are a pair of red wires (one large & one small) in a single connector plugged into the spot labeled "Ignition Unfused." With the key off I checked that plug and no voltage. With the key on I checked and there was 12+ volts. I also checked the two red wires in case they were feeding the ignition system but they were dead. Before I plugged those two wires back in, I started the engine and then turned the key off and the engine stopped! I plugged the two wires back in and started the engine again but this time it didn't shut off with the key, so I reached under the dash and pulled those two wires out and the engine shut off. That's interesting. There was another spot on the fuse box that wasn't being used, I checked it with the m-m and it had 12+ volts when the key was on and 0 volts when the key was off. I plugged the two red wires into that spot and everything seems to be working like it's supposed to. Go figure? :hmm: The two red wires have been in the Ignition Unfused spot since I replaced the harness and now three months later it does this. Weird. In case you're wondering, the stock harness had the two red wires plugged into the Ignition Unfused spot also, which is why I plugged the new harness in there.

For now it seems to be working, but it still doesn't seem right. I'm going to keep diggin around with the m-m checking voltage. Who knows, maybe I'll find the real problem.

Thanks for the suggestions.

[Madspeed]

Hmm are you powering electric fans off that?
that fat red wire is the gig lighter that pluggs into the fuse box
I should know this system like the back of my hand .. Its been a lil bit since I played with one though
I can allmost tell you what every color wire goes to
Lemme know what ya find

[Yelcamino]

Yes I have electric fans, but they're powered via relays. Power to switch the relays on/off comes from the fuse box. I've been busy over the weekend but will make it a point to investigate further this week.

Thanks.

Herb