Sudden Power Loss Mystery

[TopBanana72]

1972 Charger, factory wiring.. I've had the car for 5 years and it has never done this...

I've been working on the carb in the garage. A couple of times now when starting the engine, I will experience a sudden loss of power. All power out; lights, dash, starter... everything. I get out and test battery with test light, it lights up. battery connections are tight and clean. I see no melted wires, no smoke. I smell no electrical smell. No blown fuses. After about 3-4 minutes, I take the negative battery cable off the battery post for a minute, put it back on and power is back fine like nothing ever happened.

I'm stumped... any ideas?

thanks in advance

 

[blue69runner]

Bad ground connection some where. Maybe your cable. Check all ground's.

 

[Ron H]

I'd 2nd the above - a poor neg- batt connection can vibrate and lose connection, check it at the post and its ground.

 

[69sunfireGTX]

Check the wiring going to the back of the ammeter or the power wire feeding the ammeter in the bulkhead connector. I have run across this before. A slightly loose connection and it will cause a no power problem as you have described.

 

[Ron H]

Check the wiring going to the back of the ammeter or the power wire feeding the ammeter in the bulkhead connector. I have run across this before. A slightly loose connection and it will cause a no power problem as you have described.

Good mention! I had this problem at the BH with a poor ignition wire connection and skanky original BH. All fine then on the side of the road with the power of a door knob. It wasn't quite over yet. A closer look, after replacing the BH, there had been some heating at the ig wire connection inside the new engine harness at the BH causing it to be loose. Had to pull this out and reinsert a new connector.

 

[72RoadrunnerGTX]

Sounds like a typical charge circuit Packard terminal failure in the bulkhead connection. Weakest link in the original design, always has been. Bypass the bulkhead connections for those two runs.

 

[Don Frelier]

Another suggestion would be to check the fusible link at the starter relay.
You should also check the engine to firewall ground.

 

[Dennis H]

Does it have a Bulkhead connector?

 

[72RoadrunnerGTX]

1972 Charger, factory wiring..

Why would it not have a bulkhead connector?

 

[TopBanana72]

Sounds like a typical charge circuit Packard terminal failure in the bulkhead connection. Weakest link in the original design, always has been. Bypass the bulkhead connections for those two runs.

Would that cause all power out?

 

[Dennis H]

Biggest culprit. Took years to run it down.

 

[72RoadrunnerGTX]

Would that cause all power out?

Any high resistance or open connections between the battery/starter relay and splice 1 will account for a “all power out” condition.

 

[Ron H]

As I posted earlier, my power gone gremlin was the ignition wire at the BH. It was a bee-itch trying to trace it down; but in my case it had an ignition run syndrome - car would start/run only with the key in start mode. Often this is either a BR or bad key switch that I ruled out. A bud went around gently moving wiring around and when he tipped the BH harness up car started. When inspecting the connections look for any indication of overheating sometimes not readily noticed until looking closer. At least for me having old eyes...so if it might be the ignition wire, the run only in start mode could be a clue.

 

[TopBanana72]

As I posted earlier, my power gone gremlin was the ignition wire at the BH. It was a bee-itch trying to trace it down; but in my case it had an ignition run syndrome - car would start/run only with the key in start mode. Often this is either a BR or bad key switch that I ruled out. A bud went around gently moving wiring around and when he tipped the BH harness up car started. When inspecting the connections look for any indication of overheating sometimes not readily noticed until looking closer. At least for me having old eyes...so if it might be the ignition wire, the run only in start mode could be a clue.

When this happened, I had the negative battery loosley on the battery post. Not real loose, it fit snugly, but bolt was not tightened. I had it that way because I was taking it off frequently while working on the engine. I tightened the bolt and, so far, no issues. I'm thinking that was it because when I took it off after the fail and put it back on, power was back. I looked at the bulkhead connector and felt for any loose wires and they seem fine. Relay wires looked fine too. I'll watch and wait for now...

 

[Gerrs69rr]

A few weeks ago I was troubleshooting my ignition just randomly shutting off just like I turned the key off! I had done all the above mentioned steps with no firm results. So I started tracing power from battery, trough bulkhead connector and when I got to back of amp gauge both nuts were tight, but I was getting 12.34 volts on one side and 10.1 on the other, so I unbolted the two wires from gauge and bolted them together, just like magic it's been a few weeks and no cutting off. I ordered an aftermarket volt gauge to add to my aftermarket gauge cluster mounted under dash which holds oil pressure and temp gauge. That's my fix, obviously I could get a new amp gauge for stock gauge cluster. WARNING, heavily tape your bolted splice until you do proper splice connection.

 

[Ron H]

A few weeks ago I was troubleshooting my ignition just randomly shutting off just like I turned the key off! I had done all the above mentioned steps with no firm results. So I started tracing power from battery, trough bulkhead connector and when I got to back of amp gauge both nuts were tight, but I was getting 12.34 volts on one side and 10.1 on the other, so I unbolted the two wires from gauge and bolted them together, just like magic it's been a few weeks and no cutting off. I ordered an aftermarket volt gauge to add to my aftermarket gauge cluster mounted under dash which holds oil pressure and temp gauge. That's my fix, obviously I could get a new amp gauge for stock gauge cluster. WARNING, heavily tape your bolted splice until you do proper splice connection.

I did the loop...just in the engine bay.

 

[72RoadrunnerGTX]

A few weeks ago I was troubleshooting my ignition just randomly shutting off just like I turned the key off! I had done all the above mentioned steps with no firm results. So I started tracing power from battery, trough bulkhead connector and when I got to back of amp gauge both nuts were tight, but I was getting 12.34 volts on one side and 10.1 on the other, so I unbolted the two wires from gauge and bolted them together, just like magic it's been a few weeks and no cutting off. I ordered an aftermarket volt gauge to add to my aftermarket gauge cluster mounted under dash which holds oil pressure and temp gauge. That's my fix, obviously I could get a new amp gauge for stock gauge cluster. WARNING, heavily tape your bolted splice until you do proper splice connection.

Sounds like excessive stud head to bus resistance. Double nut to the ring terminal may have been tight, mounting nut likely loosened up, or insulator failed from heat/resistance build up. Either way, pretty easy fix if the bus is not too distorted/heat damaged.

 

[Gerrs69rr]

I'm going to check that out.