New member here, and pretty new to the diesel equipment game. My shop has a tb135 that is acting up and I'm trying to help them figure out a solution. The starter motor just stays running when you hook up the battery terminals, even with the key in the off position. We've gotten the starter rebuilt and know its not a bad solenoid. And I believe I have narrowed it down to the safety relay or key switch. My only problem is the electrical schematic I had emailed to me is in horrible condition and I can't read any of it. I need a good quality schematic and some input on what it could be. Also not sure what circuits are normally open or closed on the key switch in any of the position. Had a hell of a day trying to ohm out wires and read a crappy diagram from my iPhone screen. Can anyone give me advice?
I'm not familiar with the machine, but starters are starters, you must have juice to the small wire on the solenoid at all times for the starter to keep running, I'd start with the key switch first, see if there's electricity at all times at the wire leading to the starter, I can't imagine where else the problem could be at, there's juice all the time at the key switch and with a bad switch its flows all the time through the switch to the starter would be my guess, or else there's a short somewhere in the wire after the starter. Track the wire back from the starter to the switch and check it at the switch, if its hot, unhook the wire at the switch and see what happens if that solves your problem fine, if not then you have a problem after the switch somewhere in the harness. As for a diagram, I can't help you with that, maybe someone else can, but I'm not thinking you need a diagram for this problem. If you have not figured it out, hook a new wire directly from the switch to the solenoid and bypass the whole harness to figure out if its a problem in the harness for sure.
You say you know it's not the solenoid, but I've seen that be it way more than any thing else. Have you tried pulling the little switch wire off and putting the battery cable back on? The contacts will weld together if they get overloaded, sometimes they won't release if the voltage is low, and I went to one once where a little screw had fallen out and in between the contacts. If it cures it when you take the little wire off, see Randy's post above, he covered that well.