Technical Not starting using the key

[mu0chn]

Hi.
Has anyone got a wiring diagram for the starter system.
One of our vans would not start at a garage forcourt the other day and the driver asked if someone could have a quick look. They told him it needed a new starter and the van was pushed into a parking space.
I went and had a look and the first thing I did was check the connection on the solenoid. Found that it was bolted on and not pushon so I put my test meter on and turned the key, now power so using one of the test leads I touched the live wire in the fuse box and the starter worked and it fired up.
I have a push switch I could fit but if I can trace the fault it would be better.

Jes

 

[mu0chn]

Have fitted the push button and can now turn the engine over from inside the van. I put jump lead's from my van because it has not been used for about 15 days, engine turns over fine but won't fire.
Tried putting it back as it was and using the wire as before and still will not fire.
Anyone any ideas please.
Jes