Where is the relay switch for the coolin fan for the 1999 plymouth voyager se

are you asking is there one or for us to search endlessly for it?
why not post the symptoms and ask for diagnosis.??

i looked for you, at alldata.com and there is NO RELAY
check fuses. first. ,first always.
read the FSM read how to test the system.
on your car (modern) the PCM controls speed.
the PCM uses MPH as inputs and brake pedal switch
and then operates a SINGULAR
speed control module .
called
the vehicle speed control servo (has 3 solenoid valves inside and 4 wires)

the module is dead if the brake switch fails. 100% dead
wires,
1 brakes off.
2 ground.
3: vacuum solenoide
4: vent solenoid.... these are not real pin numbers. its a list.

very possible as it would be to accommodate the upmarket version

Someone would need to check the fan relay for voltage and then jumper it to see if the fan will run.

You would need the wiring diagram for that circuit to test the relay, one wire is battery power, one is power from the key switch, one is a ground signal from the computer, and the fourth goes to the fan motor.
The engine temp sensor tells the computer when the engine reaches 220 degrees and the fan is needed.

se encuetra detras de la luz izquierda

I have to assume you have lost the cover for it, as the schematic/Map, is on the underside of it.

sounds like a faulty motor or relay

Check you replaced the correct fan control sensor switch (not the temperature gauge sender),
Check fan fuse,
Check fan control relay operation,
Check fan will run if power applied directly to it.

Should be located in front of left frame rail (pictured below). May have to remove the left headlamp capusel and air intake cover to gain access to relay. You may also try from underneath vehicle before removing these components.

the cooling fan module is located under the air cleaner box on the radiator core support. very common problem .it is flat and about 3 inches long held on with 2 5.5mm bolts.