Great walking bass line, it's got pace but don't rush it,
keep the grove nice and steady
Main riff:
G----------------------------------------|
D--------------------4-6-6/8/6-6---------|
A--6---------3-4-5-6-------------3-4-5-6-|
E----2-4-6-4-----------------------------|
Play this as many times as it does on track...
[ Tab from: https://www.guitartabs.cc/tabs/s/stevie_wonder/i_wish_btab_ver_3.html ]
...and then go into this bit:
G------------------------------------|
D--------------------------------6---|
A------5---------7---8-7-8-----6---6-|
E--6-8---6--8-10---8-------5-4-------|
G-----------------------------------|
D-----------------------------------|
A------5---------7---8-7-8-----7/13-|
E--6-8---6--8-10---8-------7-6------|
Then just dive back into the main riff
