30 = LIVE feed
87 = output(live to fan when switched on
85 and 86 are the "coil" terminals(nothing to do with ignition!!), so so long as one of these is live and one earth this will pull the contacts closed so joining 30 and 87 allowing current to flow, if relay doesn't have diode, and most don't it doesn't actually matter whic way these two go(85 + 86).
What you have done should work, IF you are defo 100% sure the fan is switched earth ?, if it were switched live this will not make it work as it would then have two lives, when one must of course be earth, most are switched LIVE.
tabetha