24 volt charging problems .2 12 volt batteries 1 battery 16volts and the other about 9-10 volts

11 1/2 to 12 1/2 is not charging . That's less then battery state of charge , Battery stat of charge should be 12.6 volts , when charging with a volt meter you should see 13.1 to 14.1 volt at the battery posts . Is there a battery symbol lit on your instrument cluster ? Is there battery B+ voltage at the wires hooked to the alternator How to Test an Alternator

if you want the same voltage but with increased capacity connect positive to positive and negative to negative on each successive battery ---connected in parallel
example 6 X 12 batteries each of 200 crank hours will be equal to 12 volts and 1200 crank hours ( good for mobile fridges , winches , battery hoists etc)
if you want to increase voltage in the bank then connect positive to negative for each successive battery ---connected in series
for example
with 6 X 12 batteries of 200 crank amps you will have 6 times the 12 volts which equals 72 volts and the current flow is increase from 200 crank amps to exceed the 1200 crank amps because of the electrical principles and formula I think it works out to be around 72 times the 200 crank amps ( I am sure that there are mathematicians out there that will adjust the sum to make it correct)
However I think that you get the idea
when charging batteries it is always positive to positive with the battery leads to the first battery in the bank and the difference is if in parallel the charger has to be big enough the charge at the accepted rate of the batteries ( 12 volts charge at 14.5 volts and around 20 amps an drop back as the batteries charge
when the batteries are in series it all changes and best talk with a good battery supplier as to how it is set up and if you need to change the charging circuit and equipment

An unloaded reading of 10 Volts on a 12 Volt car battery is considered dead. There are 6 cells in a typical lead acid (car) battery - each provides 2 volts. They are internally connected in series to provide 12 volts on the + and - posts. If one is cell shorted out - you'd see 10 volts if fully charged. Trickle charge the battery for 24 hours and measure voltage again. If 12 volts, bring it to be load tested. that will tell you the true state of the battery.

24 volts is way to high, the battery should be 12 volts, the alternator should put out 13 volts up to 15.5 volts, if the alternator belt is excessively loose, it wont charge properly, if the belt is tight check the alternator output, (you can ck it at the battery) make sure the output is a minium of 13 should be not less when reving the engine up a little the voltage should increase, but not above 15.5 volts

did you have your alternator check

First put your battery on a slow charge 6-8 hrs.then check the batteries voltage it should have at least 12-12.8 volts if it does'nt then you need a new battery.If has 12 volts after its charged and goes dead after its installed in the car then you need a new alternato.

The first thing to do would be to put the battery on a slow or trickle charge for about 24 hours. It may be worn down enough from sitting that it needs to be revitalized. This should do it if the battery is still good. While it is charging, clean up all your cable ends and terminals to bare shiny metal. Do the battery, starter and alternator and the grounds in the engine compartment. Once the battery is charged up try it again. If the car will only start once or try to start once and need to be boosted, you will need a new battery. If it starts and runs repeatedly, then get the output checked on the alternator. A new one should charge at 14-14.5 volts but as long as it shows better than 12 volts it should be okay. Also when you are testing it, turn all your accesories on, radio, heater, A/C operate power accessories and watch to see how the alternator handles the load. The needle on your meter will bounce a little but should come back to where it was. If it doesn't then you will need to replace it as well. Hope this helps.

Yes, the extra Voltage can overload the Relay. You have several problems here. The Batteries are suppose to be connected in such a way to give you 12 Volts. If you are measuring Voltage to the Relay without the engine running, the main battery cables must be wrong. But one of your batteries must be shorted because two X 12 Volts is 24 Volts, not 16. Unless your dash Voltmeter is pegging out at 16 Volts; you are really getting 24. Use a Multimeter set to Volts and retest to see what the actual Voltage is.

If you are measuring Voltage after the engine is running, the Regulator is bad and allowing too much Voltage in the system which can burn out about anything designed for 12 Volts. It would not be much of a factor for the Glowplug Relay though, because it should shut off before you crank your truck. So in theory you would not be generating 16 Volts while the Relay was working.

You can get a free load test on the Batteries and the Starter at Autozone, Oreillys, and Advance autoparts. Ask for a charging system test. Some Walmart stores will test, but I do not know if it is free.

I hope my solution is very helpful in providing you some items to check to cure your problem.

On some of the older style GM's you can take that brown wire and cut it and take the end leading from the alternator and hook it directly to the hot terminal on the alternator and just leave it hooked up and it will work. But I have ran into the occasional problem where leaving it hooked up will drain the battery when the vehicle isn't running. Hope this helps..

have the battery tested, a shorted cell in the battery can cause an overchargre (anything over 15 volts) condition, also verify at the battery that the system charging voltage is 16 volts.