Okay, running -tsls- 'works' on my data and produces the post-estimation tests which allows me . Thanks for your assistance on this.
I do have a conceptual question about assessing and selecting suitable instruments, however. When assessing them in running OLS models, I'm often finding that at least one of them shows up as significant, but if my reading of IV is right, a 'suitable' instrument cannot have its own independent effect on the response, only via its correlation with the endogenous variable. Correct? Otherwise, I'm left with just one variable which passes, but which doesn't quite make F > 10 on the weak IV test and no Sargan calculation (tough, you may say).