Was told best to leave lights on and electrical equipment on while getting jumped as not to cause electrical problems,i once jumped a wagon,to find a fault with the anologue tachograph.Any pointers,or do most dont bother with that method.?
prob depends on how old the unit your jumping is. but it wouldnt suprise me if its ■■■■■■■■, that they just want someone to turn up in a van to jump it, and charge you a fortune for the pleasure 
Been doing it years on old cars and bikes with no issues. On trucks as long as you remeber that you have 2 batteries in line to give you 24volt you should be ok.
But
On some modern cars the manufacturers don’t reccomend jump starting as a power surge can damage complex electronics.
as a mechanic my self you are right in what your saying about the newer wagons. jumpstarting can blow the ecu, having the lights on takes away the load going to the ecu.
or you can put the negative on the chassis of the flat truck instead of the battery!
when removing the jump leads from the truck that you have just started, it can cause a power spike and blow the ECU, to avoid this, turn on as much electrical stuff as possible, such as lights, heater, radio
Our firm has been advised to leave both vehicles running for at least 5-10 mins after jumping before you take the leads off. This gives time for the charge to even out between the vehicles and avoid a 'spike.
shuttlespanker:
when removing the jump leads from the truck that you have just started, it can cause a power spike and blow the ECU, to avoid this, turn on as much electrical stuff as possible, such as lights, heater, radio
This is spot on, only need to equalise voltages if batteries are so flat even the tacho doesn’t light up. below 4v ish