Randomly wont crank, but will start with starter jumpstart

[Uku]

So basically wont crank anymore, current guess is ignition switch but will try to short it tomorrow and see if it does anything.
Will start with shorting starter connections.
At the spot when i needed to drive, i googled a bit and found about starter relay? behind gloves compartment, so removed that but it seems good.(not sure if it was right one, i squeezed my hand from bottom up and it didnt *click* when turning key to start, there were 2 relays that didnt *click*, only 1 of 3 *clicked*)
For extra info, my ignition is really worn out and it only works well with 1 key, that is without buttons, but has been starting well with that, if it use other keys, ignition will stay on and ignition barrel will keep on rolling, but i dont problem is the key.

What else should i check?

[theWalkinator]

Jump the starter relay then try to start with the key, if it starts then test the relay, if relay is good then the control side wire to the relay is not sending voltage, go from there, it might be the ignition switch, or EWS or a broken wire.
https://ww2.justanswer.com/uploads/VI/VirtualWrench/2014-04-02_233925_starting_circuit.jpg

[Uku]

Thanks for good info, but i tried with jumping ignition switch and it starts well like that. I removed ignition switch and tested with multimeter and it gives connection.
With that i guess something in key barrel wont engage long enough to turn ignition enough ?
I will try with ignition switch connected and turn it without key assembly and see if it does anything.

[Uku]

So ignition switch and key barrel all seems well, but i measured the incoming positive wire and as soon as ignition switch gets to "Start" position , voltage drops to 0v.
So why is that ?
Picture for better understanding:
https://imgur.com/a/kagESaz

[JimLev]

This is from a 98 diesel, m42/m43
What does the voltage read at #5 when you turn the key to START?
Have you checked the battery posts and clamps to make sure they are clean and tight?

725143
725142

[Uku]

Thanks for tip, I currently dont wanna disassemble that, will check if that is the cause after i finish other e39, but i checked on other e39 junction box, and that connector was really rusted out, so most likely that might be the cause on current daily.
Will update after checking it.

[Uku]

Solved, connector at junction box was totally corroded and no contact.

[JimLev]

Thanks for the update.
Guess you forgot to tell us that the vapor barrier had let water into the pass side floor.

[Uku]

I think it was caused more by the bottom hole cover had came off at some point and i drive alot gravel roads and from there, most of water and gravel gotten in, but might be vapor barrier also or water gets in from under cowl electrical box as on my other e39 did.