update on 1979 K10. Everything dead but the lights
 

The truck just quit awhile ago and I started changing everything. After this cold weather I started it yesterday and let it run for 30 minutes , shut it off started it again, etc. Seemed to be fine. Last change was fusible link at starter and thought it did the trick. Today went to garage, turned key, buzzer came on, fan started, dash lights,,went to start and dead. No crank at all. If you shut key completely off and start again, same,,got buzzer,fan,etc but no crank when turning the key to start. I still have headlights so that side must be working but dead when starting. As I said before yesterday seemed fine and today nothing. I,ve changed battery, alternator, starter, fusible link at starter, ignition switch, key cylinder, checked fuses,,,????. Am I looking at a new wire harness? Any ideas would be appreciated.
Thanks

Re: update on 1979 K10. Everything dead but the lights
 

I wouldn't throw out the whole harness.
Think basics.
What is the battery voltage on the lead battery terminals? The actual battery not the cables or bolts...
Is the battery voltage the same on the lead terminals as the battery cable terminals? Or at least within .01V...

Do you get battery voltage (within .1v) from the starter BAT lug to the block after you twist the key to the CRANK position, killing everything, and leave it in the ON position with everything dead?

What's the voltage read from the alternator case to the + Battery lug with the key still left in the ON position? Within .1V of the battery itself?

Re: update on 1979 K10. Everything dead but the lights
 

actual battery-12.43
at terminals-12.42
starter lug to block-12.39
alt to battery-12.24
Everything dead when under truck then fan came back on after a minute or so.

Re: update on 1979 K10. Everything dead but the lights
 

You've got Gremlins... but also a good starting point to troubleshoot.

You're doing voltage drop tests and you exposed a possible problem.

You've exposed a possible ground cable issue at the engine end... You should've seen 12.38 or 12.39v from the Alternator to the battery. You got 12.24v... a .18v drop doesn't indicate a good stout connection from the ground cable to the alternator bracket. At most you should see a .03v drop like you see at the starter... .18v is 6x .03v on a much shorter cable than the one at the starter. That ain't good.

Remove the ground cable and clean up the connection to the alternator bracket. You may also want to remove all the alternator mounting bolts, clean em up, and add some Never-Seeze to the bolts before you snug em all back down.

From your test at the starter... the block seems to be getting a seemingly reasonable ground... but that can be misleading... You may be grounding from the smaller gauge body ground on the rad support, around the fenders and, through the cab ground strap to the LH head. If that's the case it'll disappear when you actually ask it to pass enough current to turn the starter.

The next place to test if the ground doesn't fix it...
Do you get at least 12.38v from the J-Studs on the firewall to the block after you twist the key to the CRANK position, killing everything, and leave it in the ON position with everything dead?

Re: update on 1979 K10. Everything dead but the lights
 

also make sure that when you take off the alternator ground that you have one of those washers that kinda look like a snowflake and cut into the alternator bracket as well as a lock washer . I have a 71 Monte Carlo and that was missing made the ground intermittent..

Re: update on 1979 K10. Everything dead but the lights
 

I went down and took the neg off alt bracket and filed it and wire for good connection. Now got 12.41. Still no start. Put charger on battery at 40a for a few minutes still no start. Put it on 225a boost and truck fired right up. Load meter on battery didn't show bad. It's a brand new battery. I'm going to let 2a trickle charge all nite. I don't feel it could be as simple as a bigger battery? I don't really know about this j stud on firewall to check voltage. Didn't see anything to put meter on. Something else goofy,,the resistor for the fan blower i changed and the fan would come on high when you turned key. With the 225 boost connected the blower came on low as it always did?? Do i need it connected and running to start truck?
Thanks again

Re: update on 1979 K10. Everything dead but the lights
 

You're getting closer. It takes patience to troubleshoot wiring. If you don't have patience wiring will teach it to you. If you're getting extremely frustrated step back for a few minutes or hours to compose yourself. If it was easy everyone would do it.

The battery is just fine. It reads 12.43v cold and you've load tested it.

You have a solid ground and power connection to the starter now through the 2ga battery cables. You didn't before you fixed your ground. When you fix the rest of the problem it'll crank easier and charge well.

The starter should crank when you bypass the truck wiring with a remote starter switch across the BAT and S terminals on the solenoid.

If the cab power is completely dropping out when you turn the key to CRANK and staying off when you release it back to the ON position it's usually the battery cables or the three major distribution points...

You've verified the 2ga cable connections.

The last two major distribution points are the firewall J-Stud pair and the ignition switch.

Your ignition switch is new... I wouldn't completely rule it out but I'd check elsewhere first. I would take a gander at the plugs on the Ignition switch and make sure they're firmly seated in the sockets on the switch. Easy to check but probably not the issue.

In 1979 the J-Stud should have a fusible link feeding the ignition switch feed wire through the firewall bulkhead plug. This feeder wire is marked Circuit 2E in the wiring diagrams. If the wiring is original the alternator BAT wire is attached to the J-studs through the same fusible link as the RED Circuit 2E wire. Both studs should measure out to within .03v of full battery voltage all the time... the feeder wire that runs down to the starter BAT stud isn't switched.

NOTE: If the power weren't dropping completely out when you turn the key to CRANK and staying off when you release it back to ON I'd check the connections to and from the Neutral Safety switch or the clutch interlock switch and or the adjustment of whichever switch you have...

Re: update on 1979 K10. Everything dead but the lights
 

I'll get after it again tomorrow. This is great information. I'm pretty sure wiring is original because my father in law bought new. More confused than frustrated at this point. This J-Stud thing is a question. I'll trace wire from alt. to see if I can locate it. They all seemed to end at the fuse box block and that looks like a lot of fun,,,but we'll see. I'm more mechanical than electrical at troubleshooting. Let me add a couple more questions. When the truck starts voltage gauge is running pretty high inside cab. Second what makes it shutdown. Does a wire get so hot it temporarily melts or something, the comes back as it cools off? I'm not understanding from one day to the next it starts and runs fine then next day nothing. And it's just sitting in garage. Thanks for all ideas and answers.

Just got back from garage. Battery after trickle charge is 12.8,,,12.8 at alt,,, Truck started right up. No blower fan running at all today? Looked on firewall for this J-Stud. Nothing. Is it down behind the distributor. Something there but would have to remove distributor to get to it. By pics I could find it should be beside brake booster? Will hit it later.
Thanks again

Re: update on 1979 K10. Everything dead but the lights
 

Intermittent connections are obnoxious to troubleshoot.

It sounds like there's corrosion or a loose connection that "magically heals" itself when you apply enough current to temporarily blow through the corrosion. These are miserable faults to locate but it can be done.

The J-Studs should be on a diamond shaped piece of thermoplastic between the transmission tunnel and the brake booster. I'd remove the ring terminals from each stud and clean em up even if your problem child isn't performing right now.
This guy has an 86 with the J-studs near the top of the firewall. Circled in RED. Yours' may be lower down or on the other side of the tunnel but all the squares had em.
http://67-72chevytrucks.com/vboard/a...1&d=1171316468

Buy or borrow a remote starter button with alligator clip connections so you can clip onto the starter solenoid and bypass the ignition switch without being under the truck when this intermittent crops up again. O'Rileys has a Lisle unit for less than $20. If she starts right up look at the Neutral safety switch. If she just cranks then you have a problem between the supply side of the ignition switch and the BAT stud on the starter.

Just curious how you load tested the battery?
I have a big ole heavy sheet metal battery tester with Ni-Chrome heating elements inside and a momentary toggle switch on the bottom. When I connect the clamps to a battery and switch it on it instantly draws a huge amount of current to heat those elements. The big analog meter on the front shows the charge level before and after switching the elements on for several seconds... IIRC a test cycle is around 10 seconds... It says how long on the tool. If the battery is weak it won't bounce the meter back into the green area. You can't rely on a test done immediately after you pull the battery charger leads off or switch the truck off after a drive. A weak warmed up battery will usually lie to a load test right after you pull the charger or kill the alternator. I usually let a battery settle down for at least 12 hours before I hit it with the load tester.

A couple more quick questions....
Are your battery terminals molded onto the cables or are they the strip and clamp service replacement type?
Side or Top Terminal?

Re: update on 1979 K10. Everything dead but the lights
 

I have a load tester looks like a cabbage grader. I checked at a couple different times but I'll let it sit and try again. Battery is side mount with molded fittings on the ends. Re-did the neg 12 ga wire running to body ground from the terminal. could that j-stud be on the inside of the truck on firewall? I spent last hour going over every inch of firewall and no j-stud connector. I hear what you're saying about every chevy truck but it ain't there. The battery wire from alt. goes into a wrap along top of motor and goes down to top of bellhousing into a wrapped plastic tee. One leg goes under truck and other comes up by brake booster then to fuse block. I'm going to put the truck back up on the lift to see if i can see anything under truck that looks like it. I would have to pull the motor or transmission to service that tee,,it's that tight. I'm going to clean some stuff up around the pond and let all this sink in for awhile. It's hard to find something when it's not broken. Shook every wire I could find in and out of the truck to try and shut it down but nothing.
Thanks again

Ran truck in garage for 30 minutes. Stop,start,,,,,Battery when running voltage 14.64. After shutting down battery 13.66.

Re: update on 1979 K10. Everything dead but the lights
 

It'd be on the firewall somewhere near the one in the picture.

The firewall disconnect should have two RED main power wires. One from the starter Fusible Link that goes directly to the bulkhead plug corner socket and one from the J-Studs fusible link that goes to the middle of the bulkhead plug.

Sounds like someone doctored the wiring a bit. The deviation from the factory wiring is probably your failure point. It's probably in the plastic wiring tray.

If you have AC there should be four wires running to the J-Stud;

1. Incoming from the BAT lug on the starter.
2. To the middle of the bulkhead plug through a fusible link.
3. To the Alternator BAT lug through a fusible link.
4. To the AC/Heater Blower relay on the AC box through a 40A fuse or a fusible link.

The Alternator sense lead on plug terminal #2 goes down to the starter through a fusible link.

I'd get a J-Stud off a junked square and put it back on your firewall... Or get a battery power stud from a speed shop. Then I'd run the wires back to it using ring terminals and fusible links the way they belong. Not difficult to fix at all. Just time consuming.

Download the 1979 wiring diagrams. The stuff you're looking for is on the first long page.

Re: update on 1979 K10. Everything dead but the lights
 

appreciate all the info. I think I'll just use it to run around the farm for a while. If it quits pull it back with a tractor. If I'm going to rewire it I need to do it right. Easier for me to just pull the motor and start over. I've got plenty of other vehicles to use while this one is tore down. I've been building a 1936 chevy 5 window coupe. A lot of time invested.
Maybe my old friend will run and never quit again! Who knows. Again thanks for all the help.

Re: update on 1979 K10. Everything dead but the lights
 

The wiring deviation that replaced the J-Studs is loose and or corroded. This is your gremlin. It will be back.
Loose connections can cause an electrical fire and they do heat up the wire making it brittle.
Trying to charge the battery through a corroded or loose connection certainly will not help the alternator to live a long prosperous life.
It'll be cheaper to repair it before it burns out the alternator and much easier to repair it before you have an electrical fire.

Cheers.

Re: update on 1979 K10. Everything dead but the lights
 

I was having this same trouble on my '94 2500 diesel truck. About drove me mad, wouldn't "Stay Broke" long enough to fix it. One day it died at an intersection. I had some folks push me over to the side & I went to the parts house & bought a test light, a small adjustable wrench & a small pair of vise grips. By Damn I was gonna find out what was wrong with that truck before I moved it.
Long story short that truck fed voltage to the cab by an external wire at the Pos term on the battery. At sometime the cable had been changed by PO & the connection to the little pigtail on the cable had been made not with a butt connector but with a female Bullet connector!!! It was right there in front of me all the time! They had crimped that bullet connector between those wires just like a butt connector but of course there was no way it was gonna stay tight!.
Live & learn.;)

Re: update on 1979 K10. Everything dead but the lights
 

Butt connectors leak water and usually don't get applied properly.

I usually crimp on non insulated sleeves and then add a drop of liquid electronics flux and a drop of 60:40 Pb:Sn electronics solder at each end of the sleeve. I don't use more than a 40W iron. I cover em with "marine" adhesive lined heat shrink tube.