PLEASE make it start

[The Green Tomato]

Hello Guys, I am new here and I hope this is the right place to post a question. Well, more like a cry for help. My M35A2 has a starting issue. I get no power to my gauges, fuel pump, lights... etc. MOST of the time. I can let her sit for a day or two and it will start with the ignition switch and the button but after I turn it off... nothing, dead in the water. Here are the details:
25.3 volts at the batteries
new magnetic relay
new ignition switch
connections and grounds all good

There is only one thing I have noticed that is different from when it was running fine and that is when it will run, the battery gauge jumps into the red when I give it gas and then drops back into the green when I let off the peddle. Almost like the alternator is pumping out way too much power. Oh, ya, and the alternator is new too! It's not a generator, replaced it when it died.

This just started and left me in the parking lot at work one day. Anyone with ideas? I am so lost. Thank you.

 

[NDT]

The problems are related. When the alternator pegs out, the connection to the battery has been lost and the alt is "self exciting" without a reference voltage. If you are SURE that all the cable connections to the various posts are spic and span, and your batteries test good, look for this comes and goes gremlin which can be based on temperature and humidity: INSIDE the cable terminals, between the wire strands and the terminal, corrosion can form which acts like a semiconductor. If there is white crumbly corrosion coming out of the terminal end near the rubber insulation, this might be your problem.

 

[The Green Tomato]

Thank you thank you, I will check but all the battery and starter terms are clean. Do you think the wiring in other parts of the harness could be corroded?

 

[NDT]

Sure, these trucks are old now and any cable between the frame and battery, between the batteries, and the smaller gauge cable leading from the positive battery terminal to the engine area are all suspect. Remember the cable end terminals can be super clean while the corrosion lurks inside the terminal where you cannot see it.

 

[Bulldogger]

It sounds to me like you have corrosion or breaks inside the jacket of the battery cables. It’s not that expensive to replace them and eliminate that as a potential cause. I’ve bought a lot of old vehicles and have replaced many a battery cable.
Bulldogger

 

[The Green Tomato]

Thank you very much! I think I will see if replacing the wiring is something I can take on or if I should just find a new harness and put it in. It is pretty simple looking and I have replaced harnesses in several older Jeeps before that were a bit more complicated. However... I may be asking for more help as I dive into this project. Winter will be here soon in Colorado and I have to get it moved so my wife can park in the garage! Maybe she can just park under the Duce...? Thanks again!

 

[fasttruck]

Battery terminal issues will increase geometrically if the PO put those auto parts store "fits all" clamp on type terminations on the battery wires. Soldered or crimp ons work best,. especially if you have the military battery hardware and eye terminals on the wires. If the point where the ground wire is attached to the frame is dirty or loose it will interfere with the electrical system too.

 

[dmetalmiki]

Double check the batteries are the right way round. Double check whether the alternator is correctly wired.(As in) Is it a self regulating alternator, OR, Does it ( The type of alternator you fitted) require a Voltage regulator and cut out unit.

CHECK the wiring on the STARTER MOTOR and the STARTER RELAYS.

CHECK the wires to the back of ( And On )the MASTER SWITCH..and the MASTER SWITCH unit.

Check the ground wires behind the instrument panel.

 

[The Green Tomato]

Well, just an update, I spent most of the day inside of the engine bay checking wires. I think we may be on to something, the voltage at the batteries was about 10 volts higher that the voltage at the alternator. Now, I don't know that may be how it is suppose to be but I would think it should be the same. So there may be crud caking up in those wires... just like you all said! Looking forward to another fun filled day of playing with electric spaghetti. Thanks for listening and all the help!

 

[doghead]

Inspect the Posative battery cable from the battery to the starter. It goes through a hole the frame. Look for any possible rubbing through the insulation.

You can use an ohm meter to test your wires(to find if they are bad(internally corroded).

 

[NDT]

Voltage should be the same at batteries and alternator no matter running or not.

 

[cattlerepairman]

Honestly, I would use this as an excuse to go to your supply place of choice and get a length of cable and ends and make new battery cables. You can make a sleeve out of a rubber hose where it passes through the sheet metal opening as well. Plus, you know it is new and done right.

 

[The Green Tomato]

Well Guys, it has started again! She is running nicely and after removing tape, following wires and testing everything I still have no idea as to what I did to make it run. ha ha It just all of a sudden had the voltage at all testable locations all the way to the dash switch and she took off like a raped ape. I think it is some kind of corrosion in the wires like everyone says, it's the only answer since all the connections are good and there are no ware problems on the wires. Hard to trust her now, I may just pick up a new harness from Erik"s or somebody later on as I can afford it. Thank you to everyone for help, I hope I can repay the kindness one day. Now... off to tackle some oil leak issues...