Where is the starter relay located on a 2003 Nissan Sentra

SOURCE: 1996 nissan sentra

Find the big hose that comes out of the top of the radiator and follow it to the engine and that is where the thermostat is located. My advice is to be sure to get a factory thermostat and rubber gasket as it makes installation much easier. I have done it both ways and the factory one is easier to install.

SOURCE: need to bypass ignition switch on nissan sentra

it should be underneath your car in between the firewall and the engine. Now you don't want to supply direct power to your starter because you'll end up frying it. However to just start the car once you've located the starter, get a long screwdriver with a plastic handle and connect the two wires with the screwdriver.

As for a long term fix, without investing the money to replace the necessary parts. You will need to attach a wire that can handle 12v to both wires on your starter separately. Then connect the other ends of both wires to a switch that can handle 12v, and mount that in your car somewhere. Then whenever you need to start your car just flip the switch on until the car starts then once it is started flip it back off.
I know this sounds like a lot but it is very doable with about $5 and a little bit of time.

SOURCE: Location Of Starter relay switch

sometimes its the simple things. On the foot pedal for the clutch are rubber grommets that push the switch in on the manual trans. they get old and fall off or develop holes in them so the switch does not get depressed.

SOURCE: replace starter on 2005 nissan sentra

1. Remove or disconnect the following:
   
   Negative battery cable Air inlet tube Harness bracket Wiring at the starter Starter

SOURCE: I NEED A DIAGRAM OF THE FUSEBOX AND RELAY BOXES

On the cover of the fuse box indictes what each fuse/relay controls