Where is the starter relay switch located on a 2001 Infiniti QX4 not labeled on fuse cover

SOURCE: 2001 Infiniti QX4 low beam bulb replacement instructions

Look directly behind the headlight box if there is a rubber sleave covering the plug take it off. Unplug the wires from the bulb, there may be a saftey clip you will have to pry up to get it off.after you get the plug off the bulb holder should twist counterclockwise then it will pull right off.When you change the bulb just remember to wipe your body oil off the bulb before attaching it back into the headlight box. Then plug it back in and your in business. The high beam has three wires and the low beam has two wires. The bulb will have to be the right one.
God Bless You Greg

SOURCE: 2003 Infiniti G35 Starter location

Downloaded a PDF detailed service manual online. Gives you diagram and everything else you need.

SOURCE: power seat switch

It is most definitely the seat slide motor. Most infiniti drivers seats have three different motors. I30, I35's and QX4's all had problems with the seat slide motors. You can tap on the slide motor which is under the front of the seat and it will probably work for a little while, but it WILL stop working completely. There was actually a Technical Service Bulletin regarding this issue because there were so many vehicles that had this problem. I hate to see that guy waste money trying to get a circuit board rebuilt that absolutely will not solve the problem. 

SOURCE: MY 2001 INFINITI QX4 KEEPS SAYING SERVICE SOON

First off, make sure that the gas cap is tightened beyond three clicks. If it is and has been then there are many things that could be causing the light to come on. But let me start by assuring you that it is not something that requires immediate attention. The sole purpose of the service engine light is to detect malfunctions of emissions related components. If the gas cap isn't tight, the computer system detects an incorrect amount of pressure inside the tank due to vapor leaking out of the filler neck. If the cap is tightened after a period of time the computer detects the right pressure and the light will go off. However, on QX4's the most common cause of the light is oxygen sensors, or cam and crank position sensors, and finally intake valve timing control sensors or solenoids. O2 sensors measure the amount of oxygen in the exhaust gas. Normally I have seen that in damp and wet conditions these sensors are more likely to intermittenly give false readings. That being said, although the SES light is not an emergency situation, it will need to be addressed at some point, as the Engine control module takes the readings from these various sensors and automatically adjusts things like idle control, and air fuel mixture ratio, and eventually will to some point affect the performance of the vehicle. I have seen folks drive 100K miles with a service engine light on, so if you don't want to spend a 200 or so dollars right away, I would take the car to autozone, have the codes retrieved, and report back to this forum, at that point I would be able to advise you a little further. But more than likely you could continue driving the car without any driveablility issues.

SOURCE: Radiator cooling fan fuse location for Ford Taurus

The cooling fan on a ford car usually does not have a fuse. The cooling fans are controlled by a relay in the power distribution box inside the engine compartment. The box is usually located near the battery. Your owners manual should have a guide showing you what each relay in the box is for.