Tired of seeing my 68 Firebird sit in the barn. There is an intermittent electrical issue that makes it unreliable.
Electrical issues are not my strong suit.

When the issue arises, sometimes it sputters and dies or just up and dies.
When this happens, I have no dome lights or radio.
Issue magically resolves itself a few seconds or minutes later.
Car does fire, runs like a scalded dog.
Unfortunately, I've never put a meter on it when the problem is present.

While I have little doubt a total rewire is in my future, I'd like to trouble shoot the issue to determine root cause.

Any help is appreciated.
Thanks much...Don T.....

A quick and easy thing to check is the power junction block on the headlight side of the radiator support by the Battery. This is the main power feed for everything but the starter motor and tends to melt corrode in a 50+ year old car. Look it over carefully and the wire that feeds it from the battery as it can show 12 volts across it with a volt meter but under load can lose voltage/amperage if in poor condition. If ok follow wire across to horn relay on engine side of radiator support on drivers side near the top next to the radiator. Here is the factory manual, go to section 12 chassis electrical and once there scroll down to the Firebird diagram as it's mixed in with full-size Pontiacs and Tempest. https://www.firebird400ho.com/mdocuments-library/ If it wasn't for your description of the lights and radio dying I would have said coil but by your description you are defiantly loosing an electrical connection. And of course as always check your grounds.

Ignition switch maybe?

No, I thought that for a second to until I remembered he is losing his dome light at the same time.

X2 on the junction block...had the same exact thing happen to me back in the day.

Did some digging. Have some questions but aint figured out how to post pics.

Followed red wire (12ga?) thru a small hole in the rad support over to the drivers side, thru another small hole, to what I think is the distribution box. There is an open male spade on the box w/a red/black butt connected wire that seems like it "might" go there. Any idea?
[img]https://i.imgur.com/bRFyZag.jpg[/img]

Prior owner had installed dist box to where the tab was not in the appropriate hole that would prevent movement. The black wire w/a screw, the connector(metal) was touching the metal windshield washer bottle holder. I reinstalled it in its proper place after cleaning connections best I could.

Distributor is a pertronix HEI. As you know, needs 12v. It's tied into 2 wires that go to the firewall, all under tape. Circuit = keyed hot.
Red wire goes to dizzy. White and purple(?) wire go to firewall harness.
[img]https://i.imgur.com/aOrPIKe.jpg[/img]

Thanks much....don t.

Did you check out the factory manual link I gave you?. The part you are calling the distribution box is the horn relay that I described as being on the engine side of the radiator support, drivers side next to the radiator. The wire you are showing disconnected is for the key warning buzzer, not needed if you don't want it. The junction block I was talking about as I said is mounted on the headlight side of the radiator support on the passenger side near the battery. If as you said there is only wire from the battery to the horn relay then someone eliminated it. Its not necessary except if you need to change out the battery cable unless it's just connected on an aftermarket clamp on battery cable end, and then not needed at all. The wire you describe as shorting out on the washer tank mounting bracket is the main power feed I was talking about and was likely your problem. As far as the wiring and the quality of the electrical work done to that poor car before you got it all I can say is wow but unfortunately I've seen it many times with home mechanics that know just enough to be dangerous. All of those non soldered crimp on connectors and worse yet house wiring twist connectors are all an entry point for moisture and carbon build up. They will work but I call them ticking time bombs just waiting to relegate you to the side of the road. Hopefully you are all set for now until you have time to either go through that harness asses and repair if feasible or just replace as you said.

Barnbird... Thank you.

Actually, downloaded manual you recommended. Read it. Saw what you said.
I will look again for a junction block.

Learned something about a horn relay and the wire!

I am not a mechanic. Grew up w/this era's vehicles, always fixing on the cheap.
Wife calls it our mid-life crisis, but this time is different.
We're trying to do it right(big grin).

Yep..wire nuts and non-soldered connections are not right.
Trying to find a "Here's your problem" before I go head long into a rewire.
If that means stripping old tape, so be it.

Thanks again, have fun,
...don ...

There is no junction box.

A red 12 ga wire from battery pos goes thru rad support, heads towards drivers side but gets lost in tape. It all exits by the windshield washer bottle.

The existing crimp-on butt connectors I left alone(for now).
Removed wire nut, soldered the 3 wires, shrink wrap them.

For now, Im going to call it good, take it for a ride. Will bring multimeter.
If it dies,
... will check battery volts
... will check power to distributor
... any other place I should check???

Thanks much,
...don...

Alot of good points here by many members. Here's my thoughts:

Disconnect your battery. Then take the time fully inspect your wiring. Anything look like it was altered, "repaired"? Feel the wires, do they bend easily? My guess is the original wiring is in place with some issues. 50+ year old harness is a fire waiting to happen! All the harness's are available from all the parts companies a out there. They are plug & play, built to original specs, correct connectors, etc. I am replacing all of mine on my 1968 Firebird. And of course, check all ground, including instrument cluster/dash. It is a common problem.

Yep... lots of old wires, all wrapped in some kind of thin plastic sleeve that looks like electric tape.

Grounds.... I found 2 under the hood.
Battery to engine block. Rear pass side head to firewall. Cleaned both of them.
I've checked this site. Seems like there should be 3 grounds?
Will dig into under dash grounds.

Thanks all. Much appreciated.
Have fun...don...

Don never heard how the test drive went? As far as grounds some others that you did not mention are, copper braided strap from frame to body mount cage located on the passenger side rear of the engine compartment. The ground wire from the negative battery wire clamp at the battery to the inside edge of the passenger fender, they are all important but this one even more so. Also there is a few wires grounded to the radiator support on the headlight side near the battery.

Went to town for a lawn mower battery, 20 mile round trip. Zero issues, ran great.
Since it's an intermittent thing, more local drives are needed.....for a while.

Initially thought it was strange, I know for sure, there is no batt neg to fender ground.
I will add. Should have parts on hand.

Thank you for other ground strap locations. Will check em later today.

Much appreciated....have fun...don...