With a digital volt meter.
located passener side in front of battery, bolted to frame,grill
VAN
Where is the voltage regulator on a 1991 e350
Pull out the dipstick.
check wiring connections make shure they are tight or that they all got put back on. check for available voltage at starter and batteries also proform voltage drop test on starting circuit
under the passenger door bolted to the frame rail
drivers side by door under van attached to inside of frame
check odb codes and check o2 sen.
Check source for user manual.
Check the underhood sticker or the build tag.
Schrader valve on fuel rail.
Phone specs for the Samsung E250 are quite impressive for the price. Some of them include a battery life of up to five hours, bluetooth, Photocall for up to 1000 entries, camera and video capabilities.