charging prob and voltage drop on m1009

[hvillem1009]

i purchased an 85 m1009 about a month ago. when i bought it, it was running good. 2 weeks later the alternator burned out. replaced it with a reman alternator that burned out a week later. found out the wrong alternator was installed. now i have an isolated ground alternator, both were drivers side. now my problem is that when i can get it to crank the front battery is dropping voltage and the volt meter inside is dropping into red. i'll turn truck off and try to recrank and i get a very loud chattering with all the dash lights strobing. i've looked through the TM's and can't find anything that helps.

i took both batteries to have checked and they are good. took both alternators out and tested, both good. check gp solenoid and its good. i am at a loss of what to do. can someone please help point me in right direction of what i need to be checking?

 

[BigRix]

I had a similar problem the first time I tried to start mine. Turned out that the positive battery cable end was not making a good connection. I replaced it with a marine terminal end and it works fine now. If that doesn't do it I would switch batteries and see if the problem follows the battery.

 

[hvillem1009]

i did swap batteries around and still having the same problem.

i was searching on forum and found something on the doghead mod. what does this actually do?

 

[Warthog]

Did the parts house load testthe batteries?

Before starting ANY electrical troubleshooting, charge your batteries and have them loadtested. Don't guess.

Without knowing the status of your batteries, you are just guessing and wasting time.

The Doghead relay upgrade just fixes an issue with the starter. It helps keep it from staying running and breaking something.

 

[Warthog]

If you installed a non-isolated ground alternator on the passenger side, then something has fried.

 

[hvillem1009]

the batteries were load tested and passed. the non isolated alternator was installed on the drivers side. i haven't found any wires that look burned or damaged. i checked all fuses in fuse block and went ahead and replaced all of them with new ones. they all looked about 20+ years old. i want to get this fixed before i start my projects on the truck.

 

[hvillem1009]

i got it to crank today. so i decided to disconnect the battery cable from the positive on front battery to see if it would stay running. well it just died. hooked cable back up and it started the chattering noise and lights flickering on dash and no start. tried cranking several times and no luck. voltmeter shows yellow near green. but, when i tested the leads at battery the front battery was slowly discharging. the rear battery doesn't seem to be charging very little.

i ordered some new starter relays for cucv electric, hopefully will be here in a few days.

 

[BigRix]

That sure sounds like at least one of your batteries is bad. Like suggested above they should be load tested. The old rule of thumb we used to use on our old Vat-40 was one half the cold cranking amps for 15 seconds without the voltage dropping below 9.6 volts. I believe it is getting harder to find a shop that has an old school load tester any more. We use one of the new fangled electronic testers that simulates a load and infers what would happen at full load. Call around and find a shop that has a real load tester and if they pass, do a voltage drop test on the all the battery cables.

 

[combatmech]

That sure sounds like at least one of your batteries is bad. Like suggested above they should be load tested. The old rule of thumb we used to use on our old Vat-40 was one half the cold cranking amps for 15 seconds without the voltage dropping below 9.6 volts. I believe it is getting harder to find a shop that has an old school load tester any more. We use one of the new fangled electronic testers that simulates a load and infers what would happen at full load. Call around and find a shop that has a real load tester and if they pass, do a voltage drop test on the all the battery cables.

 

[hvillem1009]

thanks for the info. i will call around and see if i can find someone that has a good battery tester. i'm also gonna check some more wires to make sure none of them have shorted to ground. hopefully i get this fixed soon.

 

[hvillem1009]

ok. got a new front battery installed. the old one was bad. i am still not getting the charging that is suppose to be there. i was looking at wire diagram and noticed that on the passenger side alternator there were 2 wires coming off the positive on back and only one wire on the ground. but the wiring diagram shows 2 wires coming off the ground. i took a pic. is the thinner wire suppose to be on the ground connector?

 

[hvillem1009]

gen#1 probs

*** COMBINING THREADS ***

i am new to this forum and i posted a thread about some charging problems. but, i have done some troubleshooting and now i am totally confused.

first- i replaced front battery. old one was bad.

second- i checked the alternator plugs for voltage with key off/on. they are as follows:

gen#1: red wire- 12.42
brown wire- 0

gen#2: red wire- 12.64
brown wire- 0

gen#1(key on): red wire- 11.4
brown wire- 11.2

gen#2(key on): red wire- 12.64
brown wire- 12.35

i noticed that with key on gen#1 had a slight voltage drop. the gen#1 light on instrument cluster will not light up when key turned to on. also some other lights aren't working, high beam ind., speedo light, and parking brake light stays on when cranked. i pulled the cluster out and cleaned contacts and bulb sockets. then i ohmed the circuit board and everything checked good. even replaced all bulbs to ensure right bulbs were installed.

the gen#1 is still not charging and i'm at a loss of what to check next. i think there is a problem with a ground but can't find it, or does it sound like an ignition problem?

any input will be greatly appreciated. by the way i work on electronics on a daily basis for c-17 aircraft, so this is just aggrevating.

 

[hvillem1009]

forgot to mention battery voltages. front battery is 12.7 and rear battery is 12.6.

 

[doghead]

Try the link in my sig line.

 

[hvillem1009]

Next time I will be sure to capitalize where necessary. I was trying to get the information typed before I forgot what I was going to say.

 

[maxpanic]

How familiar are you with the 28 volt design? You know the alternators are isolated ground, right?

Are you getting voltage to the firewall brackets?
When facing the truck with the hood open, on the left behind the batteries there is the 24/28 volt bracket and the ground bracket below it. On the right just to the left of the master cylinder is the 12/14 volt bracket. Do you have a circuit from the alternators to those brackets?
Does the truck start/run?

 

[hvillem1009]

I am a little familiar from working on one of the fire trucks in the fire department.

Well, I did some more troubleshooting and started checking wire harnesses behind instrument cluster. Guess what I found? I found several wires burnt and fused together. The main ones burnt are the wires to the starter relay under dash. I will send a photo tomorrow. As far as i can tell is that it didn't burn all the way to the fire wall. But, it did go to the starter relay. I guess now would be a good time to do the doghead conversion. Does anyone know where a good place would be to get some new wires that will match the best?

Thanks for all the help. All the post I found on here for electrical problems have been a great help.

 

[hvillem1009]

Finally, today I was able to catch a break in the rain and get some pictures of the wires in the wiring harness that are burnt. They are the Purple, Purple/White and the Red wires that go to the starter relay under dash. There were only a couple of other wire that had very minimal damage. I will be able to fix those easily. I still haven't been able to get all the way to the firewall inside due to more rain while i was taking these pictures. It looked like it didn't burn all the way to firewall. But, I am going to replace wires from starter relay to other end point.

 

[cpf240]

Wow, looks like the dreaded runaway starter the stock starter relay is famous for!

 

[hvillem1009]

I am going tomorrow to Napa to get what I need for the doghead. I was lucky that only those 3 wires burnt and not anything else.