95 f150 4.9 (m5od)
new batt. @ 12.6, new starter, new relay
still only clicks relay
if I get relay click, ignition switch and NSS are good?
Neg batt. cable insul. cracked at terminal and corrosion visible.
- problem started with hard starts mimicking weak battery, then only relay engage click.
12v + at solenoid on crank
can neg cable be the problem?

 

It can. Click this & read the captions:


(phone app link)

 

The corrosion on the negative cable could possibly be a problem. Cracks in the insulation on a ground cable won't hurt anything unless something else comes in contact with the wire that shouldn't.

Have you inspected the wire that runs from the relay to the starter? Have you inspected the cable that splits off from the positive battery post, where it hooks onto the starter, ie the large cable hooked onto the starter?

 

Thanks Steve & 88.
I replaced neg terminal, cut back 1 1/2" from terminal (I think wire/terminal is original, 23 year old). Seemed like fuel pump faster & stronger, but no Starter engage. Multiple clicks from relay (previously single)
I have new 4ga 56" cable with factory terminals for neg.(batt to starter) to put on in a.m.
Pos. (at terminal) seems a bit crappy going into insulation.
Is there a way to test pos cable in place?
And can ignition switch or neutral safety be an issue if I'm getting power to starter relay?

 

If the starter relay is clicking when you turn the key to start it would appear that that part of the system is working.
Problem is most likely going to be in the battery to relay (fender mount) solenoid to starter wiring, Battery + to starter wire, or ground.
Possibly just a bad connection (very common reason) or a bad wire.
It could be a faulty (new) relay solenoid.
You can jump the 2 big posts on that relay and see if it cranks.
You can also bypass the big cables with booster cables to test if a wire is bad

 

Thanks, Chris!
So, with bench tested starter, working relay, and hot (12.67) battery - replaced neg cable.
Got multi clicks from relay, then single. With booster, same.
All left not replaced is the pos set. (It's the 23 years old original, I think).
I don't know exactly how to test that.

 

Voltage goes straight from the battery to the starter mounted solenoid. You should get basically the same voltage at the starter end as at the battery end.
You can also switch your multi meter to ohms and check how much resistance is in that cable from one end to the other (positive cable disconnected from battery).
It may be that you have a faulty cable, but this problem more often than not comes from crappy connections. Every one of them should be shiny clean and tight.
If you go into the electrical threads section and look way back for "good old Ford has starting problems", everything you need to know about the starter circuit is in there.