Ford Transit startup without key
 

An uncle of a friend of mine has an old Ford Transit. I am not sure of the year, but I have found a 1984 picture that looks quite the same. The thing has been sitting there for some 5 years now without being started. It has a dead battery (will not even light the side indicators), so we connected it to my car (it's a 1986 Fiat Panda with a 750 engine) with a parallel connection (+ to + and - to -) and the lights worked. So I assume this is the way it should be connected, though I'm not 100% sure. Then we took off the cover from the steering wheel (we haven't got the key) and tried to find the cables to bring the van back to life. We found a red cable and a black and yellow cable (which I suppose is ground) that light up the panel and give electricity to the levers (windscreen wiper and single side indicators, horn, headlights, battery and oil press warning lights). The fuel level indicator moves as well, and we saw there still is some diesel in it. So far so good, I assume we have found the cables that are connected when you turn the key into position 2 (normal operation). If this is right, it seems to me we will have to keep those wires connected to keep the engine running, otherwise it would be like taking the key out, right? . Now we are looking for the cables to simulate the key in position 3 (start). We have tried many combinations but have not found the right one yet. On one occasion we heard a funny clicking sound, but it sounded nothing like an engine starter.
We also noticed the cables have numbers close to them. The red one has 90 and the black and yellow one has 50.
We thought it could be simpler just to fool the key mechanism, so we put some wire in the slot to press the side contacts down while we tried to turn the mechanism with a screwdriver, but it didn't work. Probably we didn't touch all the side pins.
So here are my questions:

1) Is it possible to get the van working after a 5 year standstill?
2) Is the diesel still good or is it better to replace it (or mix it) with fresh fuel?
3) Which is easier: fooling the key mechanism or connecting the cables? If we choose the key, how do we fool the mechanism? If we choose the cable, what are the ones that give power to the starter? Do we have to keep that red and ground cables (the ones that light the panel) connected while the engine is running?
4) Do those numbers near the cables mean anything? Could they give an indication as to what cables should be connected to each other?
5) Is my 750 engine enough to start the beast? I keep it near maximum revs to prevent both batteries from going dead. Did I connect the two batteries right?

Thanks
Alberto

I don't think your 750 would be enough. Just put good batteries in there (Is there 2 of them?) The weird click might be your broken starter. If you can simulate the key ON position, then just use a jump start cable from bat + to solenoid, this way it will activate the starter for sure, but key needs to be ON.

and you did not connect the two batteries right. You have to connect + and + and ground the - from the running car on the dead car.