I have a 1997 nissan sentra that i installed a new starter but still will not work some times when car is warm up. Is there a relay in the circuit that can cause is problem.

https://www.google.com/search?q=2005+nissan+sentra+1.8+starter+relay

and

https://fuse-box.info/nissan/nissan-sentra-b15-2000-2006-fuses-and-relays

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There is no relay for the headlamps . Do you know how to read a wiring diagram , how to test electrical circuits using a volt meter ? http://www.bbbind.com/free_tsb.html free wiring diagrams ! There are videos on youtube .
Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts

How to Use Multimeter to Troubleshoot Common Problems

check the firing order of the plug leads . If you have all that is required then this is the only thing left. You may be 180 degrees out on the setting

There's a master relay that stops the windows from working when the key is off.

MIGHT BE A RELAY ! LOCATED UNDER HOOD, YOU SHOULD SEE RELAY BOX NEXT TO BATTERY. MAKE SURE BATTERY TERMINALS ARE CLEANED, PUT SOME VASOLINE ON TERMINALS, RECONNECT, TIGHTEN. CHECK ALL GROUND WIRES. ARELAY BOX MAY ALSO BE LOCATED NEXT TO POWER STEERING . COULD HAVE A FAULTY SOLONOID@ STARTER, IGNITION SWITCH COULD ALSO BE FAULTY, ITS NEVER EASY TO PINPOINT ELECTRICAL PROBLEMS, PROCESS OF ALIMINATION, CHECK ALL STARTING CIRCUIT SYSTEMS, IS YOUR SHIFT LEVER ALL THE WAY IN PARK ? DOES ENGINE CRANK ? OR DEAD, NO POWER ? ARE YOU GETTING SPARK ? HOW ABOUT FUEL ? DID YOU REPLACE BOTH THE AIR &FUEL FILTERS ? THE STARTER / SOLONOID IS WHAT CRANKS THE ENGINE, I THINK YOUR PROBLEM IS THERE ! REPLACE RELAY TO STARTING SYSTEM, ARE YOUR SPARK PLUG WIRES NEW ! THEY WILL SHORT OUT ANY SPARK IF OLD, DIRTY, I SUGGEST A TUNEUP, NEW FILTERS, AND REPLACE STARTER/SOLONOID !!!!!!

if u start car alot--or hav a low batt--or dont keep vehicle tuned up-----nevr run starter more 20 sec at a time-----giv it a couple min rest

was it running when it stopped running? If it was check for broken timing belt.

This sounds like you have a bad ground somewhere, check the main grounds to your starter and engine and see if you can find one that is loose.

Your best bet is to do a Google search for "Nissan Sentra owner's forum" and find an enthusiast's forum for your car. You'll find a wealth of information on performance, cosmetic and electrical mods, maintenance, etc, for your car.