Hot start- not turning. Relay install?

[yetihair]

Hello all,
Our van has a bit of a hot start issue. If we've been driving for a long time like say Reading to Holyhead last night if we stop the van it won't turn over when the key is turned. This caught us out before when the AA came out and had a quick jiggle of the ignition wire to the back of the solenoid and claimed it to be a loose connection. In fact it seems that the van just cooled down enough for a bit of jiggling to work.
Now I have been able to start it by shorting out between the main supply from the battery to the trigger on the solenoid using a short ring spanner but it is a faff having to take all the stuff out of the boot including the bed.
I can't find my multimeter so I haven't been able to check voltage at the terminal during ignition but at one stage I did get a small spark when the ignition was turned and I reconnected the cable to the terminal so.
I think it is a case of the main ignition wire connections being poor or the cable has degraded so that I've got voltage but not enough current.
I bought some replacement 6mm2 cable to replace it but I haven't quite been able to trace it and I can see it runs inside a plastic trunking which will need to be cut open to replace the cable (unless anyone knows another way).
Does anyone know does that cable run directly to the ignition switch or does it run via the fuse box?
In the short term (I.e while I'm back in Ireland) I'm thinking a quick set up of a relay between the main positive and the ignition terminal of the solenoid triggered by the original ignition wire. I know a kit exists but I'll work something up from a local motor factors. Does anyone see any problems with that or do you think it would be easier to replace to cable altogether?
Cheers for your inevitable advice.
Gavin

[bigherb]

In the short term (I.e while I'm back in Ireland) I'm thinking a quick set up of a relay between the main positive and the ignition terminal of the solenoid triggered by the original ignition wire. I know a kit exists but I'll work something up from a local motor factors. Does anyone see any problems with that or do you think it would be easier to replace to cable altogether?
Cheers for your inevitable advice.
Gavin

It was a approved VW modification.

[yetihair]

Well, I've completed the modification. bit of a rush as I needed to get it done before driving the van back to Ireland for the last time.
The wiring is a little untidy and I had to use a weird earthing point (I'll tidy this up at a later date), but all the terminals were crimped and soldered and now the van starts better than it ever has done.