Help with new starter issue

Sounds like a direct short to earth somewhere if you lose power and volts go to zero. Sounds like it could be in the starter or starter solenoid itself. If it was me, I'd take the starter off if it isn't too hard and bench test it.
Also, why did you change the starter. Maybe there is a wiring problem passed onto the new starter.

 

Maybe try ground to the motor. A lot of that stuff on the frame is connected by rubber grommets.
Also I've been through the 42my a few times. Look on YouTube at 42mt rebuilding

 

I think I just saw your problem from what you just said.
You need a seperate relay to go between the starter solenoid and the starter button. There's too many amps going through the starter button and the ignition switch to the starter solenoid for it to work. I had same problem myself once. Wire the relay direct to positive on battery or some other high capacity terminal. Then wire the signal side of the relay to the starter button.
Another problem I had with a 52MT starter was the starter cables just weren't up to it. I doubled up the positive and negative cables to the batteries (2 positive cables & 2 negatives instead of one each). Hope this helps.

 

You either (1) forgot one of the ground wires (2) have a bad ground cable. Usually the one that goes from starter to frame. That is a very good replacement starter. Slowly back track your work. It gets frustrating sometimes. As long as that starter was not bad out of box, you will find the problem.

 

I had this same problem as well, it was the ground from the starter to the frame, we cleaned everything and put a new larger cable along with a new cable from the batteries to the frame on the negative side and it fixed the problem, hope it's something simple like that for you.

 

Electrical problems can be one of the hardest things to diagnose without a digital volt meter. Performing a voltage drop test can reveal problems not easily seen by eye. It is very easy to perform yet most mechanics do not know how. Once after many trips to the shops and replacing batteries, starter several times. My boss gave me the job. Performed voltage drop test and found the positive cable terminal at the batteries was shrink wrapped from the factory, but never crimped or soldered. I would have never found this without performing the test. Place volt meter terminals on each end of cable to be tested, no need to disconnect cables. crank engine and observe reading. Should be .50v or less. O remove ECM fuse so engine will not start. This can be done on any cable suspect If what you said is correct the cable you touched that sparked is not a very good connection. They should not spark when touched. That IS your problem.

 

you have found your problem. the cable you touched that sparked is the problem. it should not spark.