Shouldnt really matter, i had my power on and messed around with the earth and it went on..... make sure its all connected ok...power cable, 2 xRCA, blue remote wire, earth and amp > sub.....it should work if everythings connected up correctly.
If you look towards the right side under the boot carpet (near to where you get the jack out) theres a black gromet.....remove that sand it down and stick a nut+bolt thru it
cover the essential parts up with kitchen foil (dizzy cap etc etc) spray degreaser everywhere let it sit work it in with a hard bristle bursh let it sit wash off with a low pressure hose hand dry what you can peel off the foil wait about 5min start car How i do mine with no problems at all
no point faffing around testing it, can never simulate the real high temp conditions that occur in the cooling system when you class it as open it mabe too late for the engine.....dont forget our cars are 10+ years old cant expect things like the stat to last forever its cheap enough to replace, renew the coolant, whack some new hoses on if you wish and see what happens........i wouldnt even drive it let alone keep off the boost with such a essential part of engine possibly damaged.
Bit un-helpful arnt we lads........although it is lol ;) Check ebay out something like this here Soooo much shit to choose from, starlets need something like this tho the road noise is crazy on the motorway