Hi gilshultz,
I'm sorry but I didn't understand you, where exactly do I have to put the resistor? I thought the MKR shield was meant to just plug itself into GSM.
I didn't attach the schematics because the only componentes in the circuit (besides the sensor) are Arduino. I'm attaching both schematics now though.
MKRGSM_V2.3_sch.pdf (1.6 MB)
MKR485ShieldV3.0_sch.pdf (44.6 KB)
Thanks!
CG