- Definitely check all grounds. Check all connections at the starter solenoid. Anything loose there can create an open and thus no power to the car.

- Test the battery. Getting 12 volts with a meter really doesn't tell you much. Remove the battery and take it to a chain auto parts store. They will test it for free. No, they won't lie to you about the test. Batteries can and do suddenly die. They can and do develop dead cells and interior shorts. This even occasionally happens with newer batteries.

 

"Starting Circuit Voltage Drop Test".

Set your multimeter to the LOWEST DC Volts scale.

Place the leads as follows and note the voltage when turning the key to "Start"

RED = battery positive post. BLACK = battery positive cable TERMINAL END.
RED = battery positive cable TERMINAL END. BLACK = starter solenoid battery-common large lug.
RED = starter solenoid battery-common large lug. BLACK = starter solenoid starter large lug.
RED = starter solenoid starter large lug. BLACK = starter motor large lug.
RED = starter motor large lug. BLACK = starter motor case.
RED = starter motor case. BLACK = bellhousing.
RED = bellhousing. BLACK = starter motor large lug.
RED = starter motor large lug. BLACK = negative battery POST.

None of the tests should return a value greater than 0.1-.02 vDC except the starter motor large lug to starter motor case, reflecting the resistance in the field coil and armature windings. If you have a substantial voltage drop, examine the connections.

Note: This is assuming, if you have an automatic transmission, that the shift detent is in "PARK" or "NEUTRAL" and the Neutral Safety Switch is not defective, HOWEVER if this is the case you should STILL have interior lights, dash indicators, etc.

 

clean the block ground.
follow the black cable from the battery to the block
unbolt.
spray, wire brush, spray, and wire brush again and bolt it back

 

Another thing to check; 70 was the first year that Ford put a fusable link on Mustangs. It's attached to the front terminal of the starter solenoid and goes into the main harness, supplying power to the fuses, ignition switch, and light switch. This is according to Midlife who knows these harnesses better than anyone. Essentially its a short piece of 16ga wire and protecting the 12ga main power wire.

 

Look for the burned fise link wire
70 Mustang, blown fuse link

 

+1 on the block ground issue. Had trouble with that on my S code Mach 1.... Like to see some pictures of the Grabber Green....

Pat

 

Another item to check is the actual ignition "board" in the column. Mine did the same and the board had split in two. If your board is split, I was able to Zip Ty the board back together. It worked. I had a NOS switch n board so I used that instead though.

 

Neutral safety switch?

 

In addition to the negative battery cable bolting to the block there's a ground cable that runs from the back of the block or the head to the firewall. Usually it's on the passenger side over by the heater motor. Make sure that's ok. Aside from getting dirty or rusty they can just get brittle over time and break internally.

 

I had this problem on my 71 302. It was actual a single wire coming off the starter solenoid that seems to power the entire car…runs back to ignition switch…I was a larger diameter wire…check those connectors…

 

A lot of good ideas here, and I appreciate all of the feedback. A couple other things to note:

1. I checked the battery and it is still fully charged, and is only a month old at this point.
2. Checked and cleaned the ground wire to the block, it was also replaced a month ago, but I cleaned it again for good measure.
3. It is a 4 speed, so made sure it was in neutral and it's not any of the problems assosciated with an automatic.
4. The starter was also replaced last month, and the wires coming from it all seem to be in good condition.

I located the fuse link, and had to unwrap a bunch of very old electrical tape to get to it. It appears that a long time ago someone did a little work in this area as well. Is there a good chance this is the problem? This tiny thing could be the reason I have no power/lights/horn/starter or anything in the cabin?

Also since someone asked to see a couple more pics of the car

Thanks again everyone!

 

A lot of good ideas here, and I appreciate all of the feedback. A couple other things to note:

1. I checked the battery and it is still fully charged, and is only a month old at this point.
2. Checked and cleaned the ground wire to the block, it was also replaced a month ago, but I cleaned it again for good measure.
3. It is a 4 speed, so made sure it was in neutral and it's not any of the problems assosciated with an automatic.
4. The starter was also replaced last month, and the wires coming from it all seem to be in good condition.

I located the fuse link, and had to unwrap a bunch of very old electrical tape to get to it. It appears that a long time ago someone did a little work in this area as well. Is there a good chance this is the problem? This tiny thing could be the reason I have no power/lights/horn/starter or anything in the cabin? View attachment 911987 View attachment 911988
Also since someone asked to see a couple more pics of the car
Thanks again everyone!

Easy way to check the fusible link... Put your test light alligator clip on the negative battery terminal. Probe the "BAT" post on the back of the alternator. If the test light comes on the fusible link is good.

 

In the first pic, that's a pretty hefty wire to be a fuse link, and two wires connect to it. Where it disappears under the solenoid, at the red arrow, where does it actually go? The area circled in blue is insulation over a splice. That could be a poor connection. Two other wires are spliced, where do they go? They would be better if the inline splices were removed, soldered and use heat shrink or tape to insulate. Do you have a good 70 wire diagram that shows this area and the fuse link? This is different than my 69 so I can't be much help without a 70 diagram.

 

The large blue wire connects to the positive terminal of the solenoid, and each of the ones that have the splice go to the S and the I on the solenoid. I used a voltage tester on the alternator and got a light so I’m guessing it’s not the fusible link that’s the issue. All theses wires run back towards the firewall and over into the driver side. I haven’t found a good schematic for the 1970, but I’ve been looking.

 

The big blue wire is the fusible link. It doesn't look "blown". The black splice looks like something is wrong. It looks like it has resistance there and got hot. I don't think it was repaired properly. I bet if you were to push and pull on that melted splice the electricity may flicker on and off. Or it would break apart.

Here's a picture of an unmolested feed harness. The black wire leading to the positive terminal is the fuse link. It looks longer than your blue replacement wire. It looks like someone extended the brown and red wires with a butt connector so they could accommodate a shorter fuse wire.

 

I really tried to push and pull on it, but never got so much as a light flicker. The black splice definitely is a bit melted, but actually feels somewhat sturdy when pushed on it hard. But yeah all of these wires look added and extended at some point

 

It would be well worth $10 to get a new fuse link wire, a crimp connector, and some electrical tape.

 

Since you have a test light glowing at the alternator "BAT" you know the wiring is good to "A" (see photo below). You should also have power at "B" (Fuse Block), "C" (Headlight Switch) and "D" (Ignition Switch) as they all lead back to "A". If not, somewhere after "A" there is a break either in the BLK/YEL or YEL wires leading into the passenger compartment, or on the ground side between the engine and the chassis.

 

Hi everyone, just wanted to follow up and say we finally figured the problem. A handful of wires INSIDE of the ground battery terminal were corroded. As you can imagine it was extremely difficult to see these and it finally took having a skilled electrical mechanic to see it. Thanks again to everyone for all of the suggestions!

 

FWIW, if you have terminals like that pictured below, they are correctly called "Temporary Repair Terminals" and should only be used until a proper crimped or soldered terminal can be installed.