99 GMC Sonoma with brake light issues

[michael bustamante]

ok so i now own a Baby truck! a 1999 GMC Sonoma SLS with a 4.3 and 5 speed manual tranny. cool little truck.
My uncle owns a 2001 s10 4wd ZR4 with a 3.4 and auto trans.
were both having the same issue
the brake light on the driver side is not lighting up. also when we hook a trailer there no brake light on the left trailer light as well.
which wire is the brake light so i can trace this sucker down?
is this a common issue with these little trucks?
all other functions work as designed with these taillights on both our trucks

[michael bustamante]

if anyone can just post me a taillight diagram id appreciate it