the little wire basically tells the alternator how much juice it needs to supply. it goes through the light on the dash somehow and somehow 'excites' the alternator into action.

if the resistance in the loop is different on your xr2 to what it would be on the ERST, this could mean that the alternator doesn't 'know' that your battery is low and needs charging.

done know how to test or rectify this though.

bttt for clever electrical folk