My 2.5 diesel has no balast resistor. They do draw alot of current, that could be why it has trouble starting.
I have just fixed my mates 2.25 diesel because the balast resistor was on its last legs. We also found that someone had put another earth from the last plug to the block, and that was sucking all the power from the glow plugs.
Just make sure that the plugs are ok (take them out, and use a set of jump leads to power them up) They are about £20 a set i think) :lol: