Lost all electrical power? 73 C30

[bd94s10]

Everyone has posted great feedback. Many helped me when I had challenges with my 79 cranking. Here is my feedback:

-Def swap the battery as others have said. I have several extra batteries I keep on my tender at my place. After I got mine to crank (was an issue in the column so ran a push button start) I ended up having a battery that was on it's last leg. Swapped to a red top I had and blam.... helped a lot cranking

-The junction stud and the wires going to it should be checked as others pointed out. I have a Power Probe tool (cheapest place to get one is Amazon) and I was able to begin tracing wires and checking everything thoroughly. Def crawl up in the engine bay and track the wires come off the junction studs. With a power probe or test light you can ensure your getting power to each spot along the way with the key on

-I unbolted the fuse block at the firewall as it splits in two on the 79 (prob the same on your year). I found using the power probe on various connections on the fuse block showed most was in order and working fine. I found one connection that in addition to my column issue is causing mine not to start. The key is trace all the wires and check all the connections. I also used some cleaner on the electrical connections. See pics here: http://67-72chevytrucks.com/vboard/s...d.php?t=719517

-I actually cut out some wire that was nasty including a fuse link that may have been corroded. I replaced pieces that seemed pretty bad and crusty. My truck now starts fine off the push button.

The good news is the trucks are very basic overall. Although a tad stressful in the beginning you'll get it figured out!

[TheCougarine]

I greatly appreciate everyones help so far, I'll admit I'm not great at troubleshooting wiring. If I know whats wrong I can usually figure things out but this feels like a needle in a haystack kind of situation, especially given the amount of extra wiring thats been ran in this truck. I'm going to swap batteries anyway to be sure but would a battery with a short still be able to read 12.5 volts? When I tested mine with a voltmeter it gave a good reading, though I didn't see if flipping the switch on had any affect on the output.

[SCOTI]

Originally Posted by TheCougarine

I greatly appreciate everyones help so far, I'll admit I'm not great at troubleshooting wiring. If I know whats wrong I can usually figure things out but this feels like a needle in a haystack kind of situation, especially given the amount of extra wiring thats been ran in this truck. I'm going to swap batteries anyway to be sure but would a battery with a short still be able to read 12.5 volts? When I tested mine with a voltmeter it gave a good reading, though I didn't see if flipping the switch on had any affect on the output.

The batt should be about 13v. Yes, it can have a cell that's weak & show charged but when stressed the cell craps out.

[TheCougarine]

Okay guys, swapped the battery for a known good one and unfortunately it did nothing. The truck still has no electrical power and I still have not been able to get the dome light to come on since the other day. I'm at a total loss but I really don't want to have to have this thing towed to my mechanic but its looking like I might have to. Any other ideas?

[SCOTI]

Originally Posted by TheCougarine

Okay guys, swapped the battery for a known good one and unfortunately it did nothing. The truck still has no electrical power and I still have not been able to get the dome light to come on since the other day. I'm at a total loss but I really don't want to have to have this thing towed to my mechanic but its looking like I might have to. Any other ideas?

If the new batt is known to be good, the works/doesn't work scenario reeks of a bad cable connection and/or ground.

I run a ground from the batt to the frame & run a ground from the block to the frame (same spot) using the same gauge batt cable. There's usually already a hole in the pass side frame rail where it's easy to pop in a bolt & ground the cables.

[franken]

The purpose of the big ground cable is to provide a ground for the starter. It should run to the block first. Period.

It sounds like the OP has a bad connection, (not a short, or bad battery) since the power came back mysteriously, and then went away when a larger load was put on it.

You need a DVM (voltmeter), and a long (6-8') piece of temporary wire, say 12 gauge with big alligator clips on the ends.

Use clip wire and run a connection from the - side of the battery to the cab and connect to the metal of the cab. Go into the cab and ground one side of the DVM (DC Volts settings), and use the other to check for 12V in the fusebox. Or see if some lights work (don't leave them on for more than a few seconds yet.). If they stay on, you have a bad ground.

If not, the trouble is in the small + feed from the battery, which looks like it feeds from the starter up to a junction on the firewall. Try measuring to your new cab ground from the junction block. Voltage?

Run your new wire from the battery to the junction block and check the lights. You may want to clip to the wire terminals on the wires leading to/from the j-block, but the terminal connections themselves may be bad. You may need to feed the feed the engine side of the fusebloc by the master cylinder next. I think its a big red wire from the junction block. Check lights.

The big cables run the starter, but like I said, the small + wire coming up from the starter is fed by the big + cable.

With the truck in park/neutral sou can alsu run the starter solenoid (which runs the starter, so don't kill yourself or a wall.) to see what happens. If the starter turns, the high current side is fine. If you can, measure across the battery terminals while the engine is cranking. What's the voltage?

This should provide some ideas...

[TheCougarine]

Okay cool, I appreciate the input I'll have to try that out tomorrow and see what happens.

[TheCougarine]

Okay guys I was able to check some of this stuff out today and heres what I've found. The ground appears fine and didn't seem to have any affect on anything but when I ran a wire from the positive battery terminal directly to the junction block I got power back, lights and radio came back on and the starter would just barely crank. So this means the trouble is in the wire that runs from the starter to the junction block?

[hatzie]

Originally Posted by TheCougarine

Okay guys I was able to check some of this stuff out today and heres what I've found. The ground appears fine and didn't seem to have any affect on anything but when I ran a wire from the positive battery terminal directly to the junction block I got power back, lights and radio came back on and the starter would just barely crank.

So this means the trouble is in the wire that runs from the starter to the junction block?

Correct.

There should be two ring terminals and three wires on the starter BAT terminal.
In the wiring diagram you'll see two small wires in one ring. Those are the fusible links off the starter. One is your Ammeter and the other is your junction block power.

I don't see the smaller wires in your pictures. I only see the battery cable on the starter BAT terminal.

Everything about that second picture is a red flag. The Previous Owner made a mess down there.
--What is the black wire someone ran to a fork terminal on the starter? I bet one of those is to your ammeter.
--What is the fat green wire? Where does it go?
--A yellow wire nut are you serious? Where do the wires from the wire nut go?
--Unsealed butt splices... that's a no-no under the vehicle where salt and water can get to em.

In the J-Block Picture...
--What does the GLASS Fuse with the GREEN and RED wires on the J block go to? Is that fuse burnt out?
--Is the HVAC blower HI fuse burnt? That's the GLASS Fuse holder with the ORANGE and RED wires. The body of the holder is brown where it's gotten very hot.

[TheCougarine]

I checked those fuses and neither were blown. I originally thought the green wire might be going back to the alternator but am not sure and now I'm thinking that could be the wire run to the junction block? I realize it doesn't look like it in that first picture but the big green wire is ran to the main battery bolt with the main power cable from the battery. The ring terminal has both the green wire and also a small black wire that is then ran back to another bolt on the starter solenoid. If there are not any other wires on the same terminal the main battery cable is on, would the fix be to run a new wire (with a fusible link of course) to the junction block? If its possible I'd like to get power back to the truck before trying to redo any of the rest of the wiring.

[Theoriginalsilverado]

Originally Posted by hatzie

The special short section of wire itself is a fuse. Usually Fusible links are sized two gauges under the wire being protected but not always. The GM wiring diagrams show the wire gauges used. PDF files of the GM wiring diagrams are in my signature.

In 1973 there are TWO fusible links in the system. They changed up where the fusible links were and how many they used on almost every year so this only applies to 1973.

#1 is a 14ga fusible link at the starter 3/8" BAT lug. It protects the 10ga RED wire that powers the Junction Stud block on the 1/4" stud. If you have the optional ammeter one of that gauges' wires will be run to a second fusible link on the same ring terminal.

#2 is a 16ga fusible link at the #10 Junction Stud. This protects TWO 12ga RED wires. One runs to the firewall disconnect plug and the other to the Alternator BAT terminal. The 12ga WHITE Alternator sense wire is on this link too.

This is the junction stud pair you'll find on the firewall. You can see there are two different size studs. In 1973 ALL of the power inside the cab comes through this junction.
In 1973 there can be a short chunk of 10ga wire with ring terminals between the 1/4" & #10 terminal or a special jumper terminal depending on when the truck was made.

It seems like you should be able to help me with a problem I have!
If you could have a look at my post, that would be very much appreciated:
http://67-72chevytrucks.com/vboard/s...d.php?t=726497

[El Dorado Jim]

any update?

[TheCougarine]

Update: I've got the truck running again. Ran a new wire from the big battery terminal up to the junction block and the truck fired right up and all the powers back. Needless to say I'm very happy. I want to seriously thank everyone in this thread for helping me, there is no doubt in my mind that it is only because of everyone here that I was able to solve my problem.

[SCOTI]

Originally Posted by TheCougarine

Update: I've got the truck running again. Ran a new wire from the big battery terminal up to the junction block and the truck fired right up and all the powers back. Needless to say I'm very happy. I want to seriously thank everyone in this thread for helping me, there is no doubt in my mind that it is only because of everyone here that I was able to solve my problem.

So, from the older GM cars/trucks that I've had.... that would/should be the Fusible-linked wire from the POS term on the starter that routes to the junction block (to supply power there) went bad.

[TheCougarine]

It appears so, I think that green wire in my pictures used to have a fusible link where that yellow connecter is. I decided since I'd already picked up the fusible links and wire that'd I'd just run a whole new wire straight up to the block. I'll probably have to go back and clean things up and make it look a little better but at least I know the truck is getting power now.

[bd94s10]

Glad you got it going. Like I said it can be stressful at first but if it ran fine before it just takes some troubleshooting. Happy New Year!

[TheCougarine]

Thank you! I appreciate it. Now I can get to addressing the other million things the truck needs lol

[hatzie]

Originally Posted by TheCougarine

It appears so, I think that green wire in my pictures used to have a fusible link where that yellow connecter is. I decided since I'd already picked up the fusible links and wire that'd I'd just run a whole new wire straight up to the block. I'll probably have to go back and clean things up and make it look a little better but at least I know the truck is getting power now.

Cool. Thanks for writing back to let us know what you found.