Where is the relay located that the brown wire off the starter solenoid on a 1970 ford mustang goes to

Under the hood on the inside of the fender. Round black and battery cable goes to it.

It goes to the relay

The starter solenoid/relay is on the fender lining correct? My info says, red wire with lite blue tracer, goes hot with key in the crank position and is wired through the neutral switch for automatic tranny.
Will the starter motor crank? I'm not sure, what is your problem? Any testing make sure tranny is in park or neutral and functional parking brake is set.

On the side of the starter motor the White x is the solenoid

SOLENOIDE IS ON STARTER/ARECYOU LOOKING FOR STARTER RELAY

Nothing to it. The starter position of the ignition switch simply has a single wire to the small lead on the starter solenoid.
I believe the solenoid looks like this:
http://site.americanmuscle.com/yswimages/ford-starter-relay-8593.jpg
Most cars put the solenoid on the starter itself, but Ford usually mounts it on the fender.

OK, the hot cable from the battery goes one side of the solenoid and the other to the oposite side of the starter these are the larger posts now the small purple wire goes to the small post marked s (switch) and the other small wire brown goes to the post marked r (relay).

there should be a slot for each wire on back of ignition play with them till you get it right cant hurt anything

the part may not look like this but similar,no negative cables are to be connected to this.Positive to left side of solenoid,nearest the battery,and all smallar wires that will fit on the post.One cable on the right side of solenoid goes to the starter.Any other questons please ask,I will try to help,if this helps,please let us know thanks.

just follow the big wire of the selonoid right down to starter. selonoid is on inner fender,same side as battery, connected to battery