Battery Charging Issue

So, my son purchased a 1995 Mighty Max that is all beat up. Been working for months to get it running but now I have an issue with the battery charging. I have changed the battery, started, and alternator already and it will crank and run. But using a volt meter I notice it will loose power right away. Any help would be appreciated, things I have confirmed:

• When truck is off testing the batter I get 14-16 volts
  
  • Tested terminal to terminal
  • Tested connector to connector
  • Tested negative cable to main fuse box (this is there the main fuse and 80AMP charging fuse is located)
  • Tested from negative to the junction box by the drive side firewall. When off 2 of the 3 have the same voltage.
  
  
• When jumping (truck no running just passing current from another car)
  
  • Tested all the above and getting 19-20 Volts
  • When truck is cranked it drops to about 10 volts but once running it goes back to 19-20 volts
  • At this point the 3rd jump on junction box (this is the one going to the main fuse under dash) now have the correct voltage.
  • Once I remove the jumper cables the batter started loosing voltage until the truck finally dies.

I have traced as many cables as I can and I confirm:

• power from alternator is running to firewall and then over to junction.
• two cables from alternator is going inside cab to a junction under passenger kick plate
• starter is powered directly to postive terminal and than the metal connector to main fuse box which has voltage confirmed.
• checked all the ground cabled and cleaned any rust spots before tightening back down.

Question, based on the wiring diagram looks like there might be another fuse or really coming from alternator for voltage regulation. I noticed on the passenger kickplate there is a gold.brass box just below the junction panel. Is this a relay fo capacitor for the voltage regulation?

Once again thanks in advance for help, trying to make this a father/son project and avoid taking to a shop.

Thats way too many volts
voltage regulator is likely dead

voltage regulator is the black round thing on the back of the alternator if bosch typy
or if melco type you have to split the alternator open - but its probably the bosch type

The battery shouldnt be seeing more than 16 volts ever, it will be boiling dry. should be about 13v when car is off

another issue could be that the alternator you recently put in requires an external regulator, but a quick look at the back of it will confirm that


Check the voltage coming out of the alternator while its running, it should be 13.5-14.5V

Measure the voltage of the battery, it should be about the same. If it is dropping, and the alternator is putting out 13.5-14.5v then you need to check the wiring between the two, there will be a fusable link in there that could have gone if it was getting too much charge from the alternator

Not exactly related but to me this was really solid GOLD:
https://youtu.be/pjXt7_gusgM

Thanks for the advice but I have a question. Just put new alternator in from Autozone so are you saying I need to take it apart as the voltage regulator is on the alternator? So for the stupid question but I have changed out alternators on a few pre-90s cars and never had to do this before.

Attachment 26013
There should be voltage reg like that on the back of you alternator

But first you want to check the voltage the alternator is putting out between idle and 2000rpm. If it goes over about 14.5v then the regulator is no good, or it's an alternator that needs an external regulator.

I have heard the new regulators are sometimes dead on arrival. If autozone will test it for you then take it in (nowhere here does that so I'd just put the multimeter on it)

If the alternator and regulator check out fine, then we can start checking the wiring.

you dont need to take anything out of the alternator (unless you wanted to replace the voltage reg, but its a new alternator so you can just swap it for a good one)
https://www.youtube.com/watch?v=LGB6ZEjGm7Q
basically this video

Awesome info thanks everyone.

Another question, does the ECM relay having anything to do with charging the battery.

I also noticed in the wiring that contacts to the Alternator there is an extra orange wire that has clip and connects to just under the oil filter. The clip snapped so looks like someone connected to to the chassis, I assume this is a ground?

So far we are still struggling with keep this running, ALT has been inspected, Battery replaced, Stater replaced, and continuity with wires from ALT to battery is good. With a new battery it will run for 30 mins before it dies and will only charge will being jumped.

I just wonder if there is a relay or ground problem going on. The previous owner obviously took a lot of shortcuts.

So after replacing with a second ALT and Battery, still having same issues. New questions are:

• Does the ECM relay have anything to do with the charging system?
• The cables coming from the firewall to the ALT has an orange looking cable with a clip that believe connect to a tab under oil filter. What is this? The clip broke and looks like previous owner connect to a ground spot on the side above wheel.
• I also this he did some creative wiring with the negative terminal. Right below batter is a ground that looks like he cut and and rewired using that as a junction for grounding. What I can tell is one wire goes to starter, the other to the bottom of the engine, and the last to the negative terminal. Is this normal or should I have one cable with connect points?

As mentioned still in same place, when jumping everything works. Once I remove the cable the truck will run for maybe 30 min before dying. It appears that it never charges bit all wiring has good continuity and there are no issues with the fuses. Just never goes about 12amps when not connect to about car.

Any help would be great, sorry I am such a newbie.

My guess is the 'orange' wire should be the oil sender/low oil warning light. It's a good 6" longer than the alternator harness bundle and has a thick protective sheath around the actual wire. The ground loop sounds right. The original probably corroded through and they used single grounds anchored to the battery tray. Check the ground lead from the battery. Bad grounds will create headaches so make sure all the ground bolts and lead eyelets are clean and have good conductivity.

...and don't apologise for being a noob. You're asking questions - not guessing or ghetto fixing :thumbup:

Here is a better video of how to find the thing that's draining the battery: https://youtu.be/B__DqK90IIc

Don't give up ~ getting another vehicle is too expensive ~ by any chance might there be a community college nearby that has automotive technician degree certification program ? Or any other business that might do training ~ they might use your truck to train the students?