m371961

I would not think that would lose headlights either. But, who knows on a old car what has been changed and modified. I also have no diagram to look.

steverw

The only brown wire i can think of is the tach wire, and the only orange wire with a fuse is the high speed blower.

MDchanic

If the ignition hot wire were shorted to ground, I would expect:

• Immediate shutdown of engine
• Dimming of headlights, reduced speed of heater motor
• Probably able to crank engine, but, of course, with no start (alternatively, if enough current is being diverted, cranking might provoke "dead battery symptoms," like clicking of solenoid).

I would NOT expect it to cause immediate total loss of all electrical equipment, but, if the ignition switch were left on for a minute or two, then you would smell something hot, and the fusible link would burn.

So, no, the failure mode (if accurately described) does not fit with the proffered explanation.

- Eric

oldcutlass

He said that there was a fuse blown (installed replacement for fusible link). If this was the one at the horn relay power stud that fed cabin power, then yes it would be a total electrical failure. The orange wire may in fact be a red wire.

MDchanic

He said:
Yes, in 1972, the Red 12ga wire that carries current to the interior of the car has a fusible link between the wire and the horn relay stud, and feeds all internal systems except for the A/C blower on High and the rear window defogger. We know that he said that he had his blower on, but we do not know whether he has A/C, or what it was set to.

In this specific case, he said, "I was driving... with my high beams and heater on. I had to do a 3 point turn and the second I put it in reverse the car shut down."

IF he has a heat-only system, or was running the blower of an A/C system at less than High, then he could have lost all systems as described from the fusible link (or a replacement fuse) blowing.
If so, then he needs replace it with a 16ga fusible link, as original, available in any auto parts store, because a 16ga fusible link will carry 20-25A, but will blow much more slowly than a fuse, so as to avoid blowing from brief current surges, such as from cranking the engine. A fuse will blow more quickly, before there is actually a problem, unless it is rated at a higher current, in which case it will permit more current flow than the design of the electrical system will allow.


If all of the above ASSumptions are accurate, then I would suggest that this failure may have had nothing to do with the pinched, skinned wire that he found, and was instead caused by the increase in current from the backup lights turning on, unless there is a clear reason why this bare wire would have shorted to ground at exactly that moment, and never at any other time, while he drove home with his headlights and blower on.

Regardless, all of this, and his previous problem with an alternator light that would not turn off, point to this car's wiring having been seriously messed with, and he needs to go through it carefully to see what other surprises may lay in store.

Finally, I will point out that if the suggested failure mode does, in fact, describe what happened, then Eric's suggestion of running a hot wire to the coil and jumping the starter would have worked fine, and saved him a $200 towing bill, which the transmission shop is unlikely to pay, because it was caused by the car's having been miswired (fuse in place of fusible link), and not by anything they did.

- Eric

76olds

Thanks for making more sense with this thread Eric & Eric.

MDchanic

I should also make one point clear, as I realized I neglected to:

This is a major safety issue, and you've had your one warning.

Your car completely shut down, and could not be made to work, while driving.
Fortunately, this happened while making a U-turn on a quiet street.
The same thing happening on a busy interstate could be fatal, with no headlights, taillights, or four-ways, and no engine to move you off the road.

GM used three different ways of limiting current in its cars: fuses, a fusible link, and circuit breakers.
The fusible link is used as a final fail-safe, and will not blow unless significantly overloaded for a good length of time (several minutes at least).
The fuses will blow immediately, and are sized to prevent damage in the circuits that they protect.
The circuit breakers protect the power window, power top, and headlight circuits.
In the case of the windows and top, a circuit breaker is used because a temporary obstruction (little Johnny's head) may cause an increase in current draw, but you may need to use the circuit again immediately (to reverse the window and release little Johnny's head), so a blown fuse could create an impediment to quickly resolving a "problem."
In the case of the headlights, if you were to suddenly blow a headlight fuse while tear-@$$ing down a dark road, It Would Be Bad, so the headlights are protected by a circuit breaker that will disengage and re-engage rapidly, causing your headlights to flicker, but still giving you time to pull off the road.
There is no fuse or circuit breaker in the ignition circuit, which is only protected by the fusible link, because, again, sudden failure could be very dangerous, but the fusible link will take several minutes to blow, during which time you would smell something burning, and would increase its resistance before blowing, which would be seen in dimming lights and probably in reduced engine power.

What you have now is a set-up that allows for total loss of everything without warning, is outside of the parameters of the original design, and could not only result in death or injury to yourself, but also to others, and if it did, would put you on the losing end of a large lawsuit.

- Eric

joe_padavano

OK, I think that's just a tad alarmist. We've all had cars stall out while driving. It really isn't the end of the world if you have any common sense. The car still steers and stops, it just takes more physical effort without the power assist. Yes, I know clueless people who were surprised by this and froze up. That's their problem.

If you're traveling at freeway speeds, you will coast for a while. I am always aware of what's around me and continually make mental images of "escape routes" for just such an occurrence. Before we became a bunch of distracted texting morons who rely too much on nanny electronics in our cars, this was called "defensive driving".

MDchanic

Yeah, it could be, but when I think of this, I think of roads I have spent many, many hours on (some moving), like the BQE, where everyone is doing about 70, with about 5' of following distance, unusually narrow lanes, surprise pavement defects, and no shoulder, where things like this can end badly.

I have had a complete engine failure on a motorcycle on the NJ Turnpike (bad aftermarket electronic ignition), which does have a shoulder, and was able to reinstall points and drive on, but even with a shoulder that was exciting.

I have also seen people (plural) killed on the side of the road, including one gentleman killed changing a tire on Christmas Eve, with his family in the car, on the Harlem River Drive, so I prefer not to tempt fate in this way.
He's had his warning. Some people don't even get one.

- Eric

joe_padavano

You are combining two different issues here, the ability to get safely stopped if the car dies in traffic and the safety of being stopped on the side of a busy road. I'll agree that the latter is a danger, especially when everyone is looking at their phone instead of the road. Electrical failure is only one of many potential causes for the car stalling. I'm also very nervous of being stopped on the shoulder on a freeway and obviously if you have a choice, don't do it. If you must stop, I would not recommend staying with the car unless you are WELL off the road. Just climb over the guardrail and call a flatbed.

MDchanic

Exactly.

And carry flares, and understand how to lay them out (they should start at least 1,000 feet, or a five minute walk, away from your car).

But the point I make is that while it can be a bit dangerous to suddenly lose your engine on the highway, and while it can be a bit dangerous to suddenly lose all of your lights on the highway, it can be quite dangerous to lose both at the same time, as the OP did, and considering the time and money it costs to solder on a proper fusible link, I'd say it's worth it.

- Eric

stellar

Make it safe because someday when little Johnny grows up he may be driving it and as we now know he may be slightly brain damaged.