M35A2 wiring troubleshooting

[Dunkeye11]

Upon installing my new 6TL batteries to replace my value power ones! I’m getting a short on the main positive power cable and it almost melted a new terminal off......
It’s the one that connects to the front harness. I started disconnecting things and testing it for resistance. I’m sure others have run into similer issues is there a common item that fails or shorts often that I can check I did most of the lights and the high beam switch and the turn signal box and primary light switch all accessories radios and convoy lights are disconnected

 

[cattlerepairman]

Is the battery cable itself ok? The insulation becomes chafed over time and it shorts to the frame.

 

[Dunkeye11]

It isn’t in amazing shape but from the ohmmeter it isn’t shorting

 

[doghead]

You’re saying that you changed your batteries. Did you connect your negative cable last, and your positive cable arced at that point? Or after you tried to start it?

 

[doghead]

Did the truck start and function prior to changing the batteries?

 

[Dunkeye11]

Arced when connecting negative cable

it had issues with a loose terminal arcing on start before I put a screw in to tighten it to get home and replace the clamps and batteries

 

[blisters13]

I realize the ohmmeter is not showing a short, but if all you did was replace the batteries then it seems likely the problem is in that area.

Often, a chafed wire/cable will not measure low resistance or shorted until it’s moved/disturbed. Also, ohmmeters only put out a very low voltage in the test circuit, so they often give false readings in dirty environments.

If I was asked to look this over at work, I would make a very careful inspection with a powerful flashlight, moving and twisting the affected cables/wires to view all the way around the surfaces wherever they pass through anything, including clamps.

In this case, as it’s the neg cable connecting causing the arcing, it indicates to me a positive wire/cable is shorted to the frame somewhere.

-Ken

 

[Dunkeye11]

Would me connecting the batteries improperly the first time have caused any failures to the system? They were in series correctly but we hooked the positive terminal to the vehicles negative cable and then attempted to attached the positive cable and it arced so we stopped

 

[USAFSS-ColdWarrior]

Would me connecting the batteries improperly the first time have caused any failures to the system? They were in series correctly but we hooked the positive terminal to the vehicles negative cable and then attempted to attached the positive cable and it arced so we stopped

REVERSE POLARITY....
As long as all of your power switches in the cab were (properly) in the OFF position when this occurred it should not have had a detrimental impact. You simply completed a circuit (incorrectly) through the frame/grounding of your positive side of the battery.

I have not gone back to review all of your current (no pun intended) symptoms, but short (another pun) of a fried battery or a cell or two inside one or more, the truck's systems and components should not have been damaged IF the switches were OFF.

 

[blisters13]

So, if all circuits were open or “off”, there would not likely have been any damage, as there would not have been any current flow.

Since there was an arc, there was current flow. The likelihood of damage is high, IMHO. The AMOUNT of damage may still be small.

When posting queries like this, it’s best to note all the problems as best you can. For some people, connecting the batteries backwards would be embarrassing, so they might not be inclined to mention something like that. But not noting such conditions can send advice in the wrong direction, which can lead to mistakes and wasted time.

 

[Dunkeye11]

With the ohmmeter I believe I have tracked the fault down to the alternators rectifier I’m assuming it fried during the attempt to hook up improperly

but even then why would it be giving such feedback?
Also squirrels just ate all my headlight wires this week......

 

[dmetalmiki]

It is a generator fault. IF you connected the batteries incorrectly the input I.C. is fried. And now you have a full blown generator fault.
You have to change the transistors and or rectifier in the back of the unit.
As an aside, It is not possible to 'Reverse the polarity' on an alternator.

 

[Dunkeye11]

Pulled the one out of my M151 to swap in to see if that works. Going to try and get my 2 dead ones rebuilt locally if anyone even does that anymore

 

[Dunkeye11]

Moth balls and chicken wire now.... after just one night the squirrels built another nest atop the engine

 

[dmetalmiki]

That should work just fine as they (The alternators(Self Regulating)) Are fitted across a wide range of M.series vehicles.