JayEstes

i have more if you need them

How about running a wire from under S terminal to inside, and an other wire from battery + to inside. Connect a switch to the ends of the wires. Turn the key to start, if starter does not engage, do not let the key off but press the switch you just rigged up. If the engine turns over, the battery, starter and selonoid are fine.

Going from my old memory, you can undo the NSS connector at firewall and put a jumper on firewall side of the connector to bypass NSS. There are 4 wires on that connector, 2 for NSS, 2 for reverse. Can't remember the wire colors for NSS that needs to be jumped on firewall side of connector. Also, I have opened and cleaned the original ignition switches of my 69 and 70s before and used them with success.

That's correct.
Did you say everything works fine when you attach jumper cables to your battery?  Did you try simply jiggling the battery cables and battery cable connections?  Could be coincidence I guess and still a bad ignition switch.

If you don't have ACC in any key position, then definitely the ignition switch is bad, or...you also don't have BATT power! 
ACC comes from the ignition switch.

Start with the simple stuff first.  As stated you haven't jumped the starter yet.  I would check the starter connection first, then put a test light on it , starter post and cable end, and then try the jumpers direct from the battery.  remember safety first. Brian

Will it will not crank, since it has headlights and dome lights, but no radio or heater fan, maybe the ignition switch.  When it will not crank, I'd first double check for power at the S terminal on the starter relay while the key is in the crank position.  If it's the ignition switch, there should be no power at that terminal while the key is in the crank position.
I've seen a bad battery cable cause similar intermittent issues.  But in those instances nothing worked including headlights.

I agree that it is most likely the ignition switch.  The ignition switch is indicated to be bad with low voltage at the S plug and NSS properly aligned.  However, you shouldn't be hearing a click at all with very low voltage at that plug unless you have a massive voltage drop to the starter from solenoid to starter or low battery voltage.
That's somewhat ambiguous wording, at least to me.
The fact that you lose radio and other ACC accessories is expected, as power to that circuit is dropped when the key is in the CRANK position.

Thanks just figured it out haha. Had to set some pliers on the collar and tap the cable into the hole. Tight fit. Then I pushed the plastic clip to one side and sure enough it fell right into place. I chucked the cable into my drill and slowly turned it to see if it works. This cable is cut in two and I was just getting ready for the new one I ordered. 
 
Thanks again

Casey,  what's your wife's name  ? We have a very powerful prayer group.

Terry, my factory AC cars have water valve on heater hose, non-AC cars do not and coolant always circulate through heater core.

Always has for me; there is a water valve to turn off (reduce) flow through the heater core when it is off.

I like the water line going past the choke.  Does that heat up the choke if the car is hot but has been sitting?  

Yep my 351w 2V is just like JayEstes above ^^
 
Only his is clean and shiny.

danno, Mach 1 Driver, and of course Midlife got it right!  It was the contacts in the fuse block.  To me they looked clean, didnt appear to have rust.  But I used wet/dry paper on all contacts plus used dielectric grease.  Problem gone.  Just took it for a nice ride.  NO cut out with turn signals or with the reverse lights.  
Thank you guys!  Makes the cruise that much better!
And  its still Candy Apple Red!

And that back-end hop (or rear-end shift?).... idk, but it could be a mustang feature.  Best thing I did was put KYB gas-adjust shocks in all the way around.  I haven't felt back-end hop much since then - except on wash-board-y dirt roads.  Anyway, best of luck.  These cars have next to no weight on the ass-end, and so they always feel kinda light and shifty back-there on less than perfect roads.  Hope you get her rolling under you soon.  Projects that sit are the most depressing thing.  LOL.  BTW another good stabilizer feature was a 1in stabilizer bar up front.  It dramatically reduced body-roll, which may help on back-end feel.  Another approach is throw a few bags feed or sack concrete in the back - a little weight goes a long way. haha

well, here's a thought.  If you've got a good frame under there with the global west rails, and it's solid, maybe consider just going with it as is instead of trying to improve.  There is always more you can do to try to improve, but is it really needed?  A car guy generally needs a car that rolls, so what's the best path back to getting the car moving again?  I'm frequently stuck in this conundrum - maybe I'll keep her down another few months while I do all this other stuff...  time as taught me that I like the car drivable.  Now if you skip the frame improvement, you've got it on a beautiful lift, go thru and remove all the rust spots, clean the bottom, and I rattle-canned truckbed liner under there, and I really love how hard and protective that coating is on the bottom is now.  Put the stuff back in and get her rolling.  
A car in a constant state of improvement doesn't roll much.  Do good work everywhere you are working, and maybe fight the urge to improve things everywhere.  I sure have to.  My car rolls again (5 yrs it was down for restore!) it's not perfect, but damn I love hitting the streets with it more than having all these other things I need to do before I can drive it again....

well, here's a thought.  If you've got a good frame under there with the global west rails, and it's solid, maybe consider just going with it as is instead of trying to improve.  There is always more you can do to try to improve, but is it really needed?  A car guy generally needs a car that rolls, so what's the best path back to getting the car moving again?  I'm frequently stuck in this conundrum - maybe I'll keep her down another few months while I do all this other stuff...  time as taught me that I like the car drivable.  Now if you skip the frame improvement, you've got it on a beautiful lift, go thru and remove all the rust spots, clean the bottom, and I rattle-canned truckbed liner under there, and I really love how hard and protective that coating is on the bottom is now.  Put the stuff back in and get her rolling.  
A car in a constant state of improvement doesn't roll much.  Do good work everywhere you are working, and maybe fight the urge to improve things everywhere.  I sure have to.  My car rolls again (5 yrs it was down for restore!) it's not perfect, but damn I love hitting the streets with it more than having all these other things I need to do before I can drive it again....

OK, I am going to go throw a weird one at you.  Maybe your problem is related to mine, but probably not.  your problem is more likely a connection problem. However,  I had a similar radio cutting out problem with my retrosound, except mine would cut out when I revved the engine from low speed to high, but it only seemed to happen when the car was fresh out of the garage.  Also, if the car was brought back to dead idle, radio would play again -even fresh out of the garage. weird thing was, drive it a few miles, and this cut-out would go away.  
So, after me living with this for a long while, and pondering it, but not coming up with anything, a friend rides with me and sees this weird behavior and has a genius insight - he says "do you have an original voltage regulator?"  yes.  "well then, I think maybe your radio is seeing unacceptable voltages when the alternator is kicked in at higher RPMS.  The alternator kicks in much more often immediately after the car has started after it's been sitting in garage.  After you drive the car a bit, the battery gets charged up - so alternator not kicking in - and symptom stops.   Maybe you should try a new solid-state VR." 
Freaking genius insight.  Sure enough, a new solid state VR solved my radio cutting out problem completely.
Now, in your case, the radio cuts out at low speed - when another electrical system is engaged.  So perhaps the current draw of the blinker system causes the voltage the radio is getting to somehow change to a temporarily unacceptable amount.  Car equilibrates voltages are a few moments and radio comes back on.  At high RPMs voltage is sufficiently regulated to not cause a problem in the circuit.  Do you have an old-style VR with resistors on the back? is a good question to ask if you can't trace it to bad ground or bad connection.

Above image is what the back of my old VR looked like (I believe it is original with the car).  The new Solid State versions don't look like this.
Most likely, this is not your problem, but at least I stuck to the "radio cuts out" theme.  Hope this wasn't too much of a thread high-jack!
 
Jay

It could also be the float bowls gasket is leaking. I would clean up the mess real well first. Start the engine let it idle, so the carb is under pressure. See if you can detect any dripping, or seepage while engine running.  With engine off , leave overnight see if you can detect any wet spot next day.

i use a wireless type system 

I bought this one on RockAuto.com: https://www.rockauto.com/en/moreinfo.php?pk=1140173&cc=1132399&jsn=12
Mainly because it said "Professional" & it was SHINY - just being honest....

Saturday morning came early last weekend.  Got the old girl down the beach for a decent sunrise.  A few pics for anyone interested.
The big old hotel in a couple of the pics is Hotel Galvez' on the seawall.
Beach pictures taken down on East Beach.  They put too many poles up down there, making donuts a bit dangerous - but you know a few got made.
Was a nice quiet morning out with the mistress...
Jay






 




 

I bought this one on RockAuto.com: https://www.rockauto.com/en/moreinfo.php?pk=1140173&cc=1132399&jsn=12
Mainly because it said "Professional" & it was SHINY - just being honest....

It could also be a bulb issue?  Try to replace one bulb at time see if you can isolate the problem. Sometime the contact in the socket oxidized and cause mild shortage, clean contact area with dielectric grease.  Last solution, get a voltage reading on the bulb, and radio terminal