In addition to the two items above, I suggest doing an internet search for the thread "ultimate adrenergic control of erections". It is a very long read (book length) however there are a number of texts cited there that describe the overall process and which put T in the context of a lot of other things such as norepinephrine. I'm not saying T doesn't play a big role but a lot of people seem to over-focus on it and there still seems to be way too little focus on other aspects which are necessary to place T in a proper context.