Troubleshoot this electrical problem
 

Daily driver K20 in decent condition. Ignition switch start function was getting close to failure, so I installed a start button low on the dash as a backup until I could either get a new column with a key or replace the switch. I'd noticed here that getting into the column usual gets pretty involved. But it was just a precaution, switch was still working fine.

Truck had been sitting 5-6 days, started up fine, but I immediately noticed a weird humming or buzzing from behind the dash in the area of the heater control. Then the Fasten Seat Belt light came on bright. It hadn't done much but blink occasionally in years. Hit the throttle to kick it off high idle and the belt light got even brighter, so I looked at the voltmeter. Pegged all the way past 18 to the right. Electrical smell, moved the heater and blower controls around an heard a pop. But it could have been a coincidence. Shut the truck off, went to start it again and it was dead. Headlight, park lights tail lights all work. Nothing else, not even brake lights or hazards.

It was dark and not at my house so I had very little ability to check it out before my wife picked me up. And I won't be able to get back to it for a week. I'm figuring right now it is the alternator, ignition switch or something in the heater control. Obviously a fusible link is gone, not sure which one as I couldn't get a good look and haven't had much time to go over wiring diagrams yet. If you have any input please let me know.

Thanks

Re: Troubleshoot this electrical problem
 

Replace the column, or Ignition switch, remove cheesy push- button switch and replace fusible link.

Re: Troubleshoot this electrical problem
 

The electrical portion of the ignition switch is on the outside of the steering column behind the knee panel.

If your ignition lock cylinder is borked it's a bit more involved to fix but not impossible. You will have to dig into the column to fix the lock cylinder.

18v + and super bright bulbs sounds like the regulator in your alternator took a dump.
You probably now have the honor of replacing any bulbs that were lit.
If the blower motor was on it may not be happy with you.
Basically anything that was switched on got some electrical stress if it didn't burn out.

There can be two fusible links at the starter and more on the J-stud... but this varies by year. The electrical diagrams will tell you what positions and how many.

Re: Troubleshoot this electrical problem
 

2nd on the alt going bad due to regulator. Disconnect before further start attempts.

Take an assortment of fuses. Possible one or more blew.

Take an assortment of bulbs for the same reason.

IIRC - there is a separate fuse for the blower motor on the firewall side for full speed blowing.

Original start problem: bad ignition switch, worn/broken tooth on either/or sector gear or rack piece inside the column.

Take a battery charger if you have one. You can use it to keep the battery up while you test things if replacing the alt isn't possible up front.

Re: Troubleshoot this electrical problem
 

Thanks. I was thinking regulator, but I’ve only heard.of them going the other way.

Maybe I’ll take the button out and go back to the screwdriver across the solenoid terminals technique.

Re: Troubleshoot this electrical problem
 

I've seen both. I'd much rather see em stop charging than have em run away. Lot less dangerous.

Re: Troubleshoot this electrical problem
 

Finally time later this week. Looking at the diagrams, I see THERMO HW and fusible links. What’s the difference? It seems the power is coming up from the solenoid to the block, still getting to the lights but nothing to the ignition switch. I will probably bring an HEI module with me.

Re: Troubleshoot this electrical problem
 

Thermo HW are fusible links.
One of those tiny inconsistencies in the manuals.

Re: Troubleshoot this electrical problem
 

So work schedule keeps getting changed, other stuff happens and I don't get to the truck until about noon today. Have all my tools and parts, trying to be optimistic. At this point the truck has been sitting in a hotel parking lot by the Cincinnati airport for more than two weeks. Parking spot right by the passenger side, I pull in and get out, notice right away the back of the seat is tilted forward. Not how I left it. Somebody came through the sliding window, over the toolbox in the bed, unlocked it and went through everything.

No worries, nothing of value in the cab, but then of course I notice the ignition cylinder had been destroyed. Some moron had actually tried to steal a 40 year old truck worth maybe $2000-$2500 tops. Sitting under lights in a parking lot, right next to a busy road by a couple bars and restaurants that have business until early in the morning. I know you guys in law enforcement see idiocy on a daily basis, but I was blown away. I assume the penalty for stealing a '79 K20 and a 2019 Duramax are the same.

The funny part is that had he gotten the cylinder to turn, the truck was still dead. Got it drug home, knocked out the rest of the cylinder so I could get the wheels to turn and drag it into the shop. So now I guess I will replacing the ignition cylinder or the whole column, or both. I know there are some good threads here on this stuff, if you know of any off the top of your head please point me that way. Thanks again for the help.

Re: Troubleshoot this electrical problem
 

No computers,chipped keys, or PATS makes an older vehicle a much easier target for casual theives.

My column was hacked up when I got it. New\used $25 swap meet column was a simple swap. Much easier than rebuilding my original.

Re: Troubleshoot this electrical problem
 

Ya, who would've think? Stevie Wonder could have seen that coming. Squares are more valuable than you think.
Two days after buying my 85, I had a Viper alarm installed.

Re: Troubleshoot this electrical problem
 

Replaced two fusible links, new alternator. Started and ran fine with my push button and a two handed screwdriver. Fuel gauge in and out. Tested the resistor and it seems fine, but it's been an issue since forever. Nothing seems burned out. I really didn't let it run long when it had the problem.

Took the column to a guy who redid it with new and used parts while I waited. Learned a lot watching somebody who knows what they are doing. Side note, the key cylinder that O'Reilly brought him didn't work. We had to take it back to the store and get one that actually turns. He installed and adjusted the new switch, but he made me take the old one home just in case. He wasn't impressed with the new one. Detents sloppy, etc. Guess what, it didn't work. Oh for two. I called the guy and he had me install the original, tweaking the adjustment so that it would fully engage the start function.

Burned wire on one of the ignition switch connectors. It's a small gauge brown and white wire that shares a terminal with a heavy orange wire. I traced it and can tell it's been an issue for a long time and doubt its related to the recent problem. The wire is a single silver conductor. Looped around the harness a bit and then went to the firewall connector. Looks like heat was an issue all the way. Couldn't get the firewall connector off because of course the screw that holds the halves together stripped out. I replaced the wire but would like to know what it does if anyone knows. It says on the diagram "omitted with 6 cyl gauges." My diagrams are incomplete screen shots and I can't really trace it. Anyone knows what it does?

Re: Troubleshoot this electrical problem
 

That's why I'm keeping mine looking sorry.

Re: Troubleshoot this electrical problem
 

Don't know what year your truck is but it might be as easy to go to the junk yard, find a vehicle with a key in the ignition (what I did, TRUE) and take out the ignition cylinder from that veh. I had the cheesy push button on my 98 for about 5 years, found a YouTube video of how to remove the steering column...while doing the research I think that video showed how to remove the ignition lock...that was the problem with mine all the time, the ignition lock one of the pins was bad. duh!! Ignition wouldn't turn all the way.

Re: Troubleshoot this electrical problem
 

This thread explains that tan/white wire, circuit #130. Note that I misunderstood this wire in one of my posts. Read Ray_Mcovoy's post(#4) to get the correct info.

This thread has links to Hatzie's scanned manuals, including full wiring diagrams.

Re: Troubleshoot this electrical problem
 

Thanks for coming through here, kipps. I knew there was something different about that wire, which is why I wanted to know more. The fact that it’s a resistance wire makes sense given the heat issues it’s had. There was a place where a PO had taped up the burned insulation, but there were also areas I wondered if it had just happened. Makes sense since it was an alternator problem that started this whole dumpster fire.

Not sure if I will try a salvaged wire or the resistor. Probably the resistor.

Thanks again.

Re: Troubleshoot this electrical problem
 

The alternator exciter wire is the resistor on these trucks. The wire itself has a resistance somewhere around 47Ω. It's not a separate piece if the wiring hasn't been repaired or replaced. Resistance wire is used with the gauge package.

Folks that convert from warning lamps to gauges cut the 16ga exciter wire and solder in a 1/2W 47Ω or thereabouts resistor.

If the wire is crispy you may be having diode or regulator problems internal to the alternator.
http://67-72chevytrucks.com/vboard/s...d.php?t=743692