Unsolvable problem with charging system

[christian.benfell]

I've got a 77 C20 that been running great for awhile. That is until it died about a mile from home, and almost didn't make it back up the driveway. I noticed that once I got it started up again, it was reading only 8 volts. I had my alternator bench tested, and got a new battery just to be sure. When everything is hooked up properly, I'm reading about 11 volts. When the negative cable is unhooked, I get 13-13.5 volts. I've looked for bad connections and such, and I feel like I've looked at everything. Why am I getting a low voltage when my battery is hooked up properly, and a proper voltage when the negative is disconnected? (I know I shouldnt disconnect the negative while it's running, but the meter on the dash is my only means of knowing what it's reading)

[enaberif]

Don't go based off gauges on the dash as they can go bad.

What you need to do is get a volt meter and do 3 different tests. You need to test the battery when the truck isn't running and your battery should have a rest voltage around 12.8v. Then the start truck and check your voltage again and once more when you have high beams, heater and wipers on.

Also check your grounds. Battery to alternator, engine to body, and battery to frame if you want. I'm only running battery to alternator and engine to body.

[christian.benfell]

I guess I'm gonna have to go get one of those, because otherwise I'm at a loss. I never thought something as simple as an old pick up could confuse me so much. Thanks for the advice!

[enaberif]

I guess I'm gonna have to go get one of those, because otherwise I'm at a loss. I never thought something as simple as an old pick up could confuse me so much. Thanks for the advice!

You have to remember your working on a 40 year old truck and wiring and gauges can deterioate. The trucks and wiring itself is VERY basic and simple so don't over complicate it.

[Irish_Alley]

my take you have a short somewhere in the system. maybe the battery wire is sitting on the manifold. dont know if a shorted alt would show up bad in a bench test, i think it would but idk

[christian.benfell]

After using a volt meter, I get  12.6V on the battery with the truck off. When its running, I get around 14V.  So does this mean everything's fine, and my gauge on the dash is just wrong? I haven't driven it anywhere yet, because I want to be sure I won't have to push it home. The gauge drops when ever I drop it in gear, or after it starts warming up. I know the gauge might be faulty, but it's hard for me to trust my rig when I'm getting two totally different readings. Is everything as it should be, or do I need to check something else? According to the volt meter, everything is fine.. but my truck dying at a stop sign and only running at full throttle suggests something is wrong.

[enaberif]

After using a volt meter, I get  12.6V on the battery with the truck off. When its running, I get around 14V.  So does this mean everything's fine, and my gauge on the dash is just wrong? I haven't driven it anywhere yet, because I want to be sure I won't have to push it home. The gauge drops when ever I drop it in gear, or after it starts warming up. I know the gauge might be faulty, but it's hard for me to trust my rig when I'm getting two totally different readings. Is everything as it should be, or do I need to check something else? According to the volt meter, everything is fine.. but my truck dying at a stop sign and only running at full throttle suggests something is wrong.

Then what you need to do is find a way to see what the volts are from inside the truck when your driving around. As it is at the battery everything looks fine so if you check voltages inside the truck and see a difference then you could have a wiring issue somewhere.

[NCali]

Take a minute and read IRISH ALLEYS POST AGAIN


  Behind the block you have a cluster of wires going to the starter, in that cluster you have  a couple of big thick red wires going to the started. Those wires get hot from the exhaust and have a habit of melting together , melting on the exhaust pipe, breaking at the starter, especially when the guard has been removed. You will probably find your answer there