Help! Electrical problem. (Battery, alternator, starter, relay?)

[Cntymnty77]

i need some help with an electrical problem! I have no power and the truck won't turn over now. I don't even get power to anything with the key on.

I know the battery is about shot and I'm pretty sure the alternator is shot as well. I went to move the truck today and I had to jump it. I got it to crank over several times and it almost started and then it acted like the battery was dead and cranked slower and slower. I waited a while and tried it again and it started to turn over, almost started and then again.. on the second attempt this time, nothing. No power to anything. Is the battery just that shot? I would think with it being on a hot lead from another vehicle, it would still crank. I checked all fuses and couldn't find anything blown. Could this be a relay that blew?

Thanks!

 

[CK10]

Check all your leads and grounds (there are a mess of them). As you crank with bad connections they build heat and the heat increases the resistance further killing the amperage which might explain why you hear the cranking slow as you kept turning the key. My bet is on the battery to frame ground, but check everything.

 

[Cntymnty77]

Check all your leads and grounds (there are a mess of them). As you crank with bad connections they build heat and the heat increases the resistance further killing the amperage which might explain why you hear the cranking slow as you kept turning the key. My bet is on the battery to frame ground, but check everything.

Thanks! I'll check that. I just hate the fact that someone has hacked almost all the electrical on this thing and it could almost be anything at this point. Looks like now would be a good time to rewire under the hood.

 

[CK10]

I had plenty of that when I bought my truck, still planning to strip an unhacked truck of its harness soon just to have a clean one on standby. I've got a bunch of splices and wrong color wires that I'd love to be rid of and it's easier to grab another one for $50 than it is to be super particular about fixing mine. It works perfectly but every time I see one of the splices I just think about how I could do it better.

 

[diesel4me]

A dead battery will suck the juice from any other one you use to jump start it...sometimes hooking the jumper cables to only the positive cable at the battery and the ground jumper right to the engine helps ..

It would be best to charge the dead one first,or at least leave the jumper cables hooked up to the other vehicle and let it run several minutes before trying to crank it,give the battery a chance to recover..
Sometimes starting up a vehicle with a dead battery with a jump,can fry the alternator,it'll try putting out maximum amps and volts to recharge the battery--they are designed to maintain a charge in a good battery--not charge a stone dead one...

It is possible a fusible link fried during your attempts to start it--they are located in the thick red wire at the starter solenoid,usually one or two of them on most GM trucks--also another one near the power brake booster at a plastic junction block..if those fry you cant always tell by just looking at them--no power will get to the cab if they fry..

 

[Cntymnty77]

A dead battery will suck the juice from any other one you use to jump start it...sometimes hooking the jumper cables to only the positive cable at the battery and the ground jumper right to the engine helps ..

It would be best to charge the dead one first,or at least leave the jumper cables hooked up to the other vehicle and let it run several minutes before trying to crank it,give the battery a chance to recover..
Sometimes starting up a vehicle with a dead battery with a jump,can fry the alternator,it'll try putting out maximum amps and volts to recharge the battery--they are designed to maintain a charge in a good battery--not charge a stone dead one...

It is possible a fusible link fried during your attempts to start it--they are located in the thick red wire at the starter solenoid,usually one or two of them on most GM trucks--also another one near the power brake booster at a plastic junction block..if those fry you cant always tell by just looking at them--no power will get to the cab if they fry..

I'm wondering if a fuse is fried then. I've got no power to anything with turning the key. Now I just need the time to go out and hunt it down.

 

[Cntymnty77]

It is possible a fusible link fried during your attempts to start it--they are located in the thick red wire at the starter solenoid,usually one or two of them on most GM trucks--also another one near the power brake booster at a plastic junction block..if those fry you cant always tell by just looking at them--no power will get to the cab if they fry..

I can't find a plastic junction box by the brake booster to save my life. There is a "hot" relay in the middle of the fire wall but that's all I've got close to the brake booster, other than the main fuse block.

I did just notice the main ground from the battery goes to the alternator bracket and not the frame. That seems a little odd to me.

 

[CK10]

Main ground should go from the battery to the frame just below where the alternator is. Some trucks have a smaller ground run between the alternator bracket and the core support and then from the core support to the frame.

Someone has moved some electrical around on you, check to make sure the grounds from the back of the passenger head are still connected to the firewall also.

 

[dyeager535]

Pretty sure that is how mine is wired up. Or bolted to the block. Everything should be grounded (block to cab and battery, cab to battery at core support) so not an issue if the cables and connections are all good.

The starter is the single largest draw on the truck, going directly to the block makes sense.

 

[diesel4me]

The "junction block" shown below is where two thick red wires coming off the starter solenoid post (same post the positive battery cable goes to on it) ,should have a fusible link (NOT a fuse,it'll look like a cylinder on the wire,resembling a firecracker)..

---those wires are also the same ones that have fusible links in them down at the starter area--they may be run through a steel conduit pipe,or just exposed)...if any of those fusible links are bad,you'll get no power to the cab,it wont crank,and several other things wont work..

It was common practice for GM to ground the battery to the altenator bracket--most of my trucks had another ground cable to the frame,and a smaller 10 gauge wire from the negative cable to the radiator support--also a ground strap from the valve cover to the firewall...all of those need to be intact ..

 

[Cntymnty77]

The "junction block" shown below is where two thick red wires coming off the starter solenoid post (same post the positive battery cable goes to on it) ,should have a fusible link (NOT a fuse,it'll look like a cylinder on the wire,resembling a firecracker)..

---those wires are also the same ones that have fusible links in them down at the starter area--they may be run through a steel conduit pipe,or just exposed)...if any of those fusible links are bad,you'll get no power to the cab,it wont crank,and several other things wont work..

It was common practice for GM to ground the battery to the altenator bracket--most of my trucks had another ground cable to the frame,and a smaller 10 gauge wire from the negative cable to the radiator support--also a ground strap from the valve cover to the firewall...all of those need to be intact ..View attachment 226054

Thanks for the help everyone. Sounds like this truck has a lot more wiring issues than I thought it did. Half of the grounds that you guys talked about, I don't remember seeing on this thing. Hopefully I'll have time to look at it tomorrow and see if I can figure it out.

 

[dyeager535]

FWIW, not saying mine is stock, but my ground cable goes to the block, with a much smaller ground that is bolted to the core support near the battery. Then from block to body. I want to say there is another one from core support to frame, but I'm not home to look at it. There are no electrical issues in the truck, this much I do know.

Edit: Yes, above description is correct: Battery to block, block to body, battery to core support, core support to frame.

 

[76k5blazerr]

I second the fusible links. My 76 blazer did the exact same thing, no power to anything and it was a blown fuseable link coming off the junction block on the firewall.

 

[Cntymnty77]

I second the fusible links. My 76 blazer did the exact same thing, no power to anything and it was a blown fuseable link coming off the junction block on the firewall.

I finally got around to looking and I now know why my wiring is all jacked up. All fuseable links are gone. So now I don't know what the hell it is.. I'm thinking more and more about doing an LS swap and I could rewire with everything out. The only problem is I need my truck to run to go pick up the new setup.

 

[76k5blazerr]

It sucks buying something from a hack. Sometimes people just need to realize that NOT doing something is better than doing it wrong. Sounds like a complete rewire would be the way to go, then you at least know it's not going to catch on fire or something going down the road. From what I have read the painless wiring harnesses really are "painless" if your willing to pay the 6-800 bucks.

 

[Cntymnty77]

It sucks buying something from a hack. Sometimes people just need to realize that NOT doing something is better than doing it wrong. Sounds like a complete rewire would be the way to go, then you at least know it's not going to catch on fire or something going down the road. From what I have read the painless wiring harnesses really are "painless" if your willing to pay the 6-800 bucks.

They do sound painless other than the hurt on the wallet.

 

[CK10]

The lack of fusible links won't keep it from starting, burned ones would though. If they've been removed and connected without them it's the same as replacing a fuse with a piece of wire, it's definitely a no-no but as long as there is continuity you would still have power.

 

[Cntymnty77]

The lack of fusible links won't keep it from starting, burned ones would though. If they've been removed and connected without them it's the same as replacing a fuse with a piece of wire, it's definitely a no-no but as long as there is continuity you would still have power.

That's why I'm at a loss now as to why I'm not getting any power. All fuses are good and can't find any fuseable links anywhere on this thing.

However, I did notice a replaced wire from the junction block on the firewall to the starter had been touching the right exhaust manifold and melted through it. But I don't know how long it's been like that.

 

[CK10]

Do you have a multi-meter available to you? Even a cheap-o harbor freight $5 one could really help narrow this issue down.

 

[Cntymnty77]

Do you have a multi-meter available to you? Even a cheap-o harbor freight $5 one could really help narrow this issue down.

No, I've got an idiot light but I could probably find a meter.