The starter relay on a 1999 GMC Suburban with the bib block engine is located on the solenoid for the starter. The solenoid for the starter is on top of the starter.
Inside fuel tank,
a defective starter switch
It is screewed into the side of the engine block, right in front of the starter.
I have a 96 2.2 and had to drop the exhaust from the manifold in order to change the starter. and goos luck.
I had this happen on an 88 GMC Suburban. Took a while to find it. Turned out to be a ground wire under the dash
where is the starter located on a 2004 chevy suburban
How do you replace a starter in a 1999 suburban
Slide in under the truck behind the passenger side front wheel. Look UP at the rear side of the engine and you will see the starter. It will have 2 bolts holding it on.
disconnect + battery terminal take out 2 bolt out of starter from the engine block take off the wires remebering where they go do in reverse order to reconnect
this might help you: http://www.justanswer.com/questions/194b5-1987-gmc-suburban-4x4
bad starter, or wire to starter