The power stage is behind the battery on the fender. It is likely to be held in by two slot head screws if original. You MUST have a perfectly fitting screwdriver if they are slot head as the heat and corrosion will have made these so tight they will fight you with every turn.

Clean the fender side and the back of the power stage then re-coat with thermal/heat sink paste. If they were the slotted screws, replace them with about anything else.

Be aware, this is one of three parts you should have a known good spare for. Known good is normally a used part that you install and drive around with (best if you do it in the hottest part of summer) for a couple weeks. You then put the original or the "new" known good in a baggie in the trunk/wagon spare wheel well.

The other two are the AMM (most important!) if yours is an LH 2.4 car and a fuel pump relay.

All three cannot be 100% troubleshot without replacing with a know good item and all three can leave you stranded.