1968 with no power in cab

[Captainfab]

A couple weeks ago I lost all power inside the cab of my '68. I do have power to the 12 ga red wire at the engine side of the bulkhead connector behind the fusebox. I took the connector off as well as the fuse box, checked those wire connectors, cleaned them, bent the tabs out to help make contact, reassembled but still no power inside the cab. I connected jumper cables to the battery and ran power to the horn relay connector on the inside of the firewall, and then everything inside the cab works. Is it common to have to replace the connectors inside the bulkhead connector and back of the fuse box on the 12ga red wire? Or is there something else I am overlooking? Could a bad ampmeter cause this?

[RustyPile]

Sometime, when connecting the inner and outer (inside cab to engine bay side) halves of the firewall plug, the terminal(s) will get pushed back in the connector slot.. Take a look again at those terminals and make sure one of them isn't pushed back and just not making contact.. As a clue, when this happens, it's usually the male terminal..

{EDIT}
I forgot to address your ammeter question.. The stock factory ammeter and its circuit isn't an "active" part of the system.. Any part of it can fail and will not affect the performance of the electrical system whatsoever.. The ammeter circuit is referred to as a shunt circuit.. Meaning it only reads the difference in voltage between 2 widely separate points on the main power distribution wire.

[Captainfab]

Thank you for the reply

The connectors are as tight in the housings as they can be. The connectors for the red, pink and purple are a little dis-collored indicating they have gotten a little hot. I may just have to try and replace those connectors and see if that fixes the issue.

Originally Posted by RustyPile

Sometime, when connecting the inner and outer (inside cab to engine bay side) halves of the firewall plug, the terminal(s) will get pushed back in the connector slot.. Take a look again at those terminals and make sure one of them isn't pushed back and just not making contact.. As a clue, when this happens, it's usually the male terminal..

{EDIT}
I forgot to address your ammeter question.. The stock factory ammeter and its circuit isn't an "active" part of the system.. Any part of it can fail and will not affect the performance of the electrical system whatsoever.. The ammeter circuit is referred to as a shunt circuit.. Meaning it only reads the difference in voltage between 2 widely separate points on the main power distribution wire.

[Second Series]

Disconnect the battery and ohm it out. Try to probe as far out as possible. You might need to use a length of wire with an alligator clip on the end if your ohm meter leads don’t reach. Connect one end to the + battery cable(battery disconnected) and the other to the horn relay connector red, or whatever is easiest to get to. With the ohm meter connected, start working and flexing the wire harness and bulkhead connector. If there is on open, it may make contact and show on the meter. If you do find the trouble area, move the probes closer until you pin-point the open.

[Captainfab]

Thanks for the reply but I determined the issue about 3 weeks ago.

Originally Posted by Second Series

Disconnect the battery and ohm it out. Try to probe as far out as possible. You might need to use a length of wire with an alligator clip on the end if your ohm meter leads don’t reach. Connect one end to the + battery cable(battery disconnected) and the other to the horn relay connector red, or whatever is easiest to get to. With the ohm meter connected, start working and flexing the wire harness and bulkhead connector. If there is on open, it may make contact and show on the meter. If you do find the trouble area, move the probes closer until you pin-point the open.

[VetteVet]

Have you solved your issue yet. I am posting this diagram which will identify
the wires you are describing so that everyone can follow along.







The firewall connector is located in the lower left corner of the diagram. It is the 12 gauge red one and we are looking at the inside of the cab. This is the main power wire to the cab and if we follow this wire up into the diagram we see that it connects to a junction with three other 12 gauge red wires. which send all the power to the cab items.
To the left of this junction in the middle of the left side of the diagram is the horn relay, which is where you connected your jumper and you got all the cab power functions by providing 12 volts to the junction. The other wires in the junction power the key switch, the fuse panel lower right, and the headlight switch to the right of the diagram.
The only conclusion can be that there is an open in the inside cab wire between the firewall connector and the wiring junction shown in the diagram.