This is a song The Band would open or close their concert with.  It was originally done by Marvin Gaye. 

(Standard Tuning: E B G D A E)

The song is simple:

    G  C       Bb  G
E|--3--------------3-|
B|--3--5-5--5---3--3-|
G|--4--5-5--5---3--4-|
D|--5--5-5--5---3--5-|
A|--5--3-3--3---1--5-|
E|--5--------------3-| Repeat this throught the entire song. 

Solo over these chords in C minor.    

Improvise around those chords to make it more interesting.  
Here's a riff to get your started.

E|---------------------|
B|---------------------|
G|-----3--3h5~-5p3-----|
D|--/5---5---------5~~~|
A|---------------------|
E|---------------------|