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My 54 Packard recently had smoke pouring into the cabin directly in the center of dash under the radio speaker. Burning electrical plastic smell and white smoke. The back up switch is a Hurst /Holley 2480003 installed in 2021. The trans is a 1985 GM 700R4. The back up light switch is in the location of the Ultramatics old reverse position and goes on when the 700R4 is in L1. The trans is perfect with new pan, filter, gasket and fluid. The smoke and smell is only when trans is in L1. In drive, all is perfect and all 4x gears shift smoothly. Has anyone every heard of a back up switch going bad and smoking? In this instance if I drive down the road in L1 only, with switch depressed and back up lights lit at 10mph going forward is the only time I get this smoke and smell. If the switch was never meant to be depressed for that long would it burn out eventually? I thought maybe leaking trans fluid on exhaust as well? but no leaks. Thoughts are welcome. This is only recent. Is there a fuse or relay attached to the switch?

No ratings are found for the switch but it certainly looks robust and should be able to handle a couple of backup lights.

Without knowing exactly where or what in the linkage activates it and how the supply wiring is connected it is kind of hard to guess what might be going on. The Hurst instructions just show a part of their shifter pushing the switch plunger and I would imagine somewhere yours is doing the same. You might check the switch to verify that is what is actually burned and also check for any damaged or pinched wires. If the shorted wire is before the switch it would be the wire insulation burning and not the switch. For the switch to be burning due to a shorted wire, the short would need to be after the switch and somewhere going to the lights. It could even be in the trunk if something slammed into the back of the trunk and damaged a wire going to one of the bulb sockets.

As to whether it is fused, that is the question. Again, without knowing exactly what was done it is a guess. If they used the wiring going to the old Ultramatic switch and just extended it so it could reach the new switch the answer may be NO and for something to burn, that is sort of what it appears to be. The backup up light feed is a black wire labeled 42D and drawings for the senior instrument cluster show it is connected to the battery post of one of the breakers on back of the cluster. That terminal is getting power directly from the ign switch accessory feed. There was a service article and on page 59 of the Oct, 54 SC dealers were asked to check the body feed wire on the other breaker which is also shown being on the wrong or BAT terminal of the breaker. The reverse light feed wire on your car may have the same issue and possibly never been corrected.

If they did something different when installing the GM trans then I believe the only action would be for you to do a wire by wire trace and find out where power is coming from.

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Thanks Howard! I'm on it. Stay tuned.

My apologies for taking so long to get back. The smoke was coming from one of the 2x wires leading to the backup switch when in gear. The switch is activated by the position of the trans/steering column lever. The green wire appears fine, the black wire is totally fried, the sheathing is melted off and has dried up and crumbled off. I disconnected the switch. I now have an exposed "hot" wire with a lot of metal around. The 2x back up light wires appear to feed into a harness type thing jammed under the steering column. very hard to navigate and put tape on. I did my best with tape but that black wire probably fried all the way thru car to cluster. Seems very dangerous to have a hot wire in engine bay. Any thoughts would be welcome.

I think you are correct with "There was a service article and on page 59 of the Oct, 54 SC dealers were asked to check the body feed wire on the other breaker which is also shown being on the wrong or BAT terminal of the breaker. The reverse light feed wire on your car may have the same issue and possibly never been corrected."

Definitely sounds like something is miswired at the breaker to have that kind of wire damage. Typically with the type breakers Packard used a short would cause the breaker to trip, stay off for a few seconds and energize again only to trip immediately and continue that cycle until power was cut off or short was removed..

If something was damaged or shorted in the bulb socket or green wire going back to the reverse lights I would have expected some indication in that wire. With only the black wire being damaged I suspect either something in the switch itself failed, maybe a terminal was positioned too close to ground or some linkage and the switch loosened or linkage moved so terminal touched. Could also be somewhere in the wire run between the breaker and switch the wire became shorted. Often going thru a sharp or unprotected hole in the sheetmetal or passing in a narrow space between two pieces of metal can damage the insulation on wiring. You mentioned it is in a portion of loom going close to other items. It may also be possible a portion of loom slipped out of position during the transmission installation and when a clamp or something else was tightened the loom and wire got caught and was pinched. Vibration or other movement could have finally caused the pinched insulation to fail.

Afraid it is going to be a tedious process and going inch by inch to find where and what might be the issue.

Thank you Howard. I'm on it.

TC

Problem solved. Thank you Howard. I used a Packard wiring diagram and followed 42 D black wire and 42 C green wire. The 42 D black wire was fried all the thru to the battery post. The post is very hard to get to. I cut the wire and all is good, just to be safe. Ideally, like you said it should be connected to the AUX post. No back up lights at the moment, but no smoke from burning wires as well. The switch was only 1 yr old and must have went bad or not compatible with 6V POS? I called Holley/Hurst (backup switch #248003), they said s/b ok 6V or 12V and either terminal is ok. Did it need some type of ground? Or was wire frayed somewhere hitting metal? What is the easiest way to get to the terminal and battery post? I cannot fit under there, how did mechanics do it? Anywho, problem solved, thanks again !

TC

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At least you found a reason for the wire burning. Too bad that issue was not discovered and repaired way back when. Other owners of 54s that still have original wiring might also want to check both breakers on their cars. Packard issued a bulletin about the body feed wire on one breaker being on the wrong terminal but apparently missed the same issue with that wire on the other breaker.

As to accessing the breaker post, I cannot give much encouragement. Any way you approach it, working under the dash is a pain. If you think the breaker is hard to reach on your car, just be thankful you do not have to do anything under the dash on a 55-6 model with factory air.

No idea how or where your switch is positioned to work with the new transmission or what is being used to activate it so cannot offer much help. All I can say is based on the photo of the switch it should handle the current needs of the backup lights without any problem but manufacturing defects do occur. Switch definitely does not need any kind of ground. Without being there it is hard to guess what happened but one possibility to carefully check is the switch mounting. Could the switch or a bracket or something nearby have loosened and the wire or terminal that connected to the breaker become accidentally grounded?

Only suggestion I would make on the new switch and wire is be double sure both are protected from accidentally touching or being caught or damaged by any metal. When the new wire is run avoid placing it thru any holes in the firewall that do not have a grommet or in any space where it could become pinched by sheetmetal or linkage or something being tightened down. On the switch, once mounted run the gearshift linkage thru the full range to make sure nothing can get close enough to touch the terminals and if the switch should loosen, make sure the terminals can not twist or drop and touch anything.

One of those "you got away with one" deals. Similar to another post the other day which had headlight wiring issues - common theme these days. These cars are ~70 years old now, don't expect then to be in good shape everywhere nor stay that way much longer without a lot of work.
Whole car and surroundings coulda went up in smoke with a bit of fuel vapors. 6V uses more amperage than 12 to get the same job done, so if those wires aren't good, they heat up and fry what insulation is left. It's a gradual vicious cycle process until the resistance becomes intolerable and acts like a toaster/cigarette lighter. {Heat causes corrosion both heat and corrosion causes resistance - repeat.} Doesn't even have to short, but that's also possible with shakey insulation. Often damage deep inside the harness also, where you can't see or detect it until it fires off. I have pictures from a rewire of such hidden "treasures".
A lot of them get "modified" or "tampered" with by owners/mechanics before you get them, rightly or wrongly. {Not good practice to direct wire off the battery w/o fuse, circuit breaker, momentary}
The factory wiring back then was not up to today's protection standards, so it won't protect itself either - unless updated. Even 12s can do the same thing. I had a horn wire fire on the Cad sitting in the garage. Paper insulator deteriorated, made casual contact, and PO made some bad repairs. Good thing the relay melted and stopped it before the whole garage.
B safe out there.

54packpac

The copy of the ’54 wiring diagram I have has this note;

At the lower part of Page 29, you will note a wire identified as "Body Feed." In the wiring diagram this wire is connected to the "Bat Post" on the back of the instrument cluster. This is incorrect and should be connected to the "Aux. Post" to provide circuit breaker protection for the rear chassis and body wiring.

Is your car wired per the original wiring diagram, or has the above observation been incorporated?

dp