I had the same symptoms about 2 years ago and it was gradually getting worse over time, it turned out to be the ignition switch and since it was replaced it has been fine.
Seems like it could be one of two things. Mihht have to google.how to change the switch to see if its a difficult job or not
Please don't take this the wrong way, but I'm sensing you're quite green when it comes to this sort of thing. Alarms are ringing because you're talking about ataching jump leads to starter which means live leads whilst rumaging around under van. If you slip and touch a lead to the wrong place it could mean disaster! If you're confident then great, but if not, don't mess with electrics and get someone over to help mate
If bench testing can only occur with a bell housing out the van I can only assume @77 Westy means do it the way I describe. Afterall bridging the connections is not exactly safe either! You are welcome to pop round and have a go
I had this issue (I think) recently and eventually traced the issue back to the small wire at the starter motor. The connection was poor at the spade itself to the cable - just pushing it into a slightly different orientation solved the issue but I really do need to change the spade connector to make a more permanent repair
Thanks for that bit of info. I will recheck all the connections too in case I have missed anything first time round
So an update on this. The lights dim all round when I turn the key but nothing. The battery is new and showing strong. Baffled now.
When the lights dim with a new battery does the starter click or not If you turn on the hazard flashers at the same time as the headlamps do the headlamps dim in time? If either happens check the battery connections. With the headlamps on see if you can measure voltage drops across things like the battery post and the clamp it is attached to or between battery negative and the earth tag beside the right hand rear light cluster. Each time you should not be able to read more than hundredths of a volt. More than that then there is a bad connection.
The starter does not click. Absolutely nothing. The headlights only have the very feitness or flicker in time with the hazards. It really is negligible. I will get the multimeter out tomorrow night and and what I can find. Too annoying.
What was the state of the 6.3 mm spade connector on the starter? Have you tried rocking the bus in gear and then putting it in neutral, then trying again. It is possible that the solenoid is jammed in the bush. If you have an original Bosch starter I have seen some solenoids on ebay of late. Did you get a wire brush or dremel and clean up ALL the connections. Sorry if you have done this, just trying to rule stuff out. It is possible the wire feed to the solenoid is broken. Might be worth running a new wire to the spade connector from the battery and see if the solenoid clicks.
It all.looks very clean and shiny up there to be honest. I've tried rocking the bus but to no avail. It is a Bosch unit reconditioned and bought from GSF 3 ish years ago. I will try to run a new wire to it and see if I can get it to operate. I think if I could bench test it that would be best. But I do not have bell housing unless my 1500 beetle one would do?