(quoted from post at 21:33:24 12/25/18) We have a 1961 4010 diesel. As we have posted and read on this forum it appears to have been correctly converted to the early 4010 system. We have installed new battery cables to the starter and a new fuseable link on the left side battery to the transmission and a new cable between the batteries. Now it turns over very slowly or not at all. The batteries are 8 months old and are holding a 12.4 charge. We have disconnected all the cables - then connected only the right hand side battery to the starter and the meter reads 0 volts, we then disconnect the cable and the meter reads 12.4 volts.
Any help in diagnosing this would be appreciated.
Also is the fuseable link the only ground cable on these tractors.
"it appears to have been correctly converted to the early 4010 system"
Battery wiring as you describe started with 4020 Serial # 91,000, but, of course, many older tractors were retrofitted.
But, NO MATTER, from the point of view of the starter, ALL 24 Volt 4010 4020 systems are electrically the same.
As it left the factory, the (+) terminal on the RH battery was connected to a terminal stud on the engine side of the starter "belly".
The (-) terminal on the LH battery was connected to the large and topmost terminal stud on the starter solenoid.
So, measuring the voltage between the two studs just mentioned should give you a voltage reading of 24 Volts (nominal), actually around 27 Volts with good, charged batteries.
And, if your little ground wire/fusible link is intact, touch black digital voltmeter lead to a nice, clean area on the chassis, and the red lead to the battery cable stud on the starter solenoid, voltmeter should read (-) 12 Volts (nominal).
Now, touch red lead to other battery cable stud on engine side of starter belly, voltmeter should read (+) 12 Volts (nominal).
Check that out, and report back.