mikerunt

hey everyone, new to the forum, new to vintage mustangs.

I have a 1966 Mustang w/ a 351W and a C4

Have recently run into an issue that I can't seem to troubleshoot. suddenly and for no apparent reason I loose all electrical power when I try to start my Mustang. What happens is I put the key in the ignition, turn to on (all fans and pumps turn on) and when I go to crank / start everything shuts completely off like I've blown a fuse. Starter doesn't even try and turn over. If I try to immediately restart I get nothing at all. Completely dead no fans or pumps. No juice at the ignition key.


I can wait about 5/10/15mins or so and then for some reason everything seems to reset and I'll get all the power at the On position (pumps/fans) again. Once I go to start and try to crank it over, everything shuts down again and no power at the ignition key at all.

I assume it it has to be a pump or relay or something that can reset it self? Not sure.

No blown fuses at stock fuse box under dash at driver side.

No MSD 6AL or aftermarket.

Could it it be a bad starter solenoid?

broken ground wire? I checked the battery negative and that seems to be good.

Any my help would be epic

Gun Jam

this actually sounds totally normal.

with everything running when the key is moved to the "start" position it will shut power off to like everything except the starter motor and the headlights.

But once the key is released the ignition should rotate it back to the left to the "run" position and shut down the starter and allow power back to all the accessories...but you are saying once it moves back to the "run" position you have no power to anything?

There are no "pumps" or relays

If the above is accurate then its likely a really bad battery.

and/or

This is one of those cases where im not being told the important part of the story.
When did it last run right?
What changed between then and now?
What else should I know that could help?

-Gun

mikerunt

hey Gun, thanks for the reply. The car ran beautifully Friday night. Came home, pulled it into the garage, shut it off, all good. Saturday AM, I woke up and went to warm to car up to take the family for bfast. Went to start it, and it did what it does which is try to crank for a bit, but nothing unusual. Rotated the key back off of start, let it sit for a second, then went to crank it again. The starter kick over for a second or two and then all power loss (while key was still in start position). Nothing, completely dead. Rotated the key back to off, then back to start and nothing totally dead still. Waited for about 10mins trying every two or three minutes to start it (with it be totally dead). After about 15 more mins of it sitting, and not attempting to start it, I went out and rotated the key to on and the pump and fan kicked on. I then rotated the key to start and everything completely died again. Did the Same routine of turning the key to off and back to start with no powrt to anything again.

mikerunt

and to to further clarify, the car does not actually start. It's when rotating the key to start that everything dies and shuts off as described above.

Coosawjack

Weak battery!!

mikerunt

I'll have a look! For some reason it doesn't feel like a weak battery because of the way it does completely, them comes back to life...

Gun Jam

The battery could be leaking power internally under load or something goofy like that that.

Check to make sure the post are clean and the terminals are tight. After cranking it over check the voltage at the battery post with a volt meter..Is it super low?

I would investigate battery issues really carefully before moving on to something else.

mikerunt

Thanks Gun, will do.

Derf00

A bad cell would act like a normal battery until a heavy load (like a starter) was placed on it. Use a VOM to test the voltage of the battery it should be 12.7vDC or higher. Have someone try to crank the motor while you continue to observe the battery. If it is a bad cell it would drop to the 11's or lower.

If the battery voltage doesn't budge, then you have a break in the ignition circuit somewhere. Depending on your system you may have fusible links which can reset over time if they're not fully broken or the solenoid is shorting out. You can then try bypassing the solenoid with a screwdriver to troubleshoot it.

mikerunt

Hey everyone, quick update. After taking all of your advice i think i've found the issue; a poor battery negative to engine block ground. This AM when going through all of the wires as suggested, that one felt a little flimsy at the neg battery post. when to the auto store, got a new cable and post cleaner, reinstalled, and then jumped the starter solenoid to test (battery positive to "S")and the car fired right up, faster than it ever has! reinstalled the started wire from ignition on the starter solenoid and it started right up again, faster than ever before! insane that something so easily overlooked seems to of made such a huge difference. thank you all again!