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HH56 - Interesting setup. I'll consider that as an option. My wife doesn't like the idea of cutting the floormat (and neither do I), so the terminal post one is probably not an option anyway. The knife blade version could work, but I can't seem to find one that takes a high enough amperage. The lever with a clevis and rod might be the best bet.

Side question - Everything online says to hook up your positive terminal first and then the negative. But I'm assuming because these cars are 6 volt positive ground, that should be reversed. Similarly, I should be hooking this shutoff to the positive side and not the negative (even though most products say to hook up on the negative side) for the same rationale. Would that be the correct logic? Thanks!

To those who have offered suggestions on products, would this one be satisfactory? It has "500A rated current, 5000A instantaneous current". It says it is 12v-36v, but I assume that isn't an issue. Same for it saying it is intended for the negative terminal setup, whereas I would want to use it on positive since that is the ground.

amazon.com/dp/B0BX346SX3/ref=sspa_dk_det ... sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWwy

Thanks!

Sacre bleu, Packriots, your Chrysler is an exceptionally lovely hue. Have never seen such a rationally sized car equipped with a second windscreen. Your Model 143 Single Eight should be visible even to the most cellphone-distracted motorist.

The switch you show above looks much like the Cole Hersees i've used in my '40 and '47 Packards since the late '70s, but for the added bracket, which seems a nuisance. As for your wife wisely not wanting the cars harmed, in my earlier Packard, only the shaft of the on/off lever went through a small hole in the floor and carpet; there was no cutting. Simple, convenient, no Rube Goldberg.

A late supercharged '37 Cord Phaeton-owning friend recounted how, in his callow youth, spiritedly driving in the '40s over a railroad grade crossing, his under-seat battery, not well secured and the covering hatch not in place, kissed its terminals momentarily against the bottom of the seat springs, for additional excitement. We pop riveted a very thin piece of aircraft ply to the underside of my '40 Packard's hatch cover, all the better as I was using not the Group II called for in the 120/160, and previous year's 319-ci Super-8, but a Group IV, used in the Packard Twelve. It b a r e l y squeezed through the opening in the floor to nestle in the underfloor battery box without taking my fingers with it.
Those were the days before the excellent Optima 800 cold cranking amp, 18 lb. Red Top 6-volt battery, which i also recommend. Know of a fellow readily starting his Cad V-16 with one, another with a '41 Cad getting 14 years service; a decade for me. In the win-win-win of no off-gassing, nor corroded terminals, less weight, which as anyone enjoying sport, GT, or road car, luxe or not, knows is the enemy.

You've a pair of sharp cars.

Marine grade for 6-12-36-volt applications. 250-amp rating at 6 volts, 15-second continuous. And you never want to grind your starter--or should have to -- longer than that. They've gone up in price a little, so shop around. Brass or silver contacts. There are cheaper ones out there, but these are durable, solidly made:

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su8overdrive - Thank you again for your continued help with my issues! I'm definitely learning as I go. You stated 250amp rating, but I'm not seeing that. I'm seeing a couple different variations - 175A/1000A and 175A/800A. I'm not sure if those numbers are reflected for a 36v setup in which case would the amperage be much higher for 6v? They also state 15 seconds on, 5 minutes off. I do agree that I wouldn't run the starter more than 15 seconds - in fact, I usually limit it at 8-10 seconds. But would that mean I couldn't try to start again for 5 minutes? Or am I misunderstanding the "5 minutes off" part? If either car doesn't start in 8-10 seconds, I usually wait about 30 seconds and try again, but being a newbie, maybe I'm doing that wrong. The benefit of the Cole Hersee model is that the stem is very long. I'd have to go through 3/4" of wood, which would in fact spare me the Rube Goldberg device.

I only recently discovered the Optima battery, but alas I've just purchased new batteries in each car, so I'll just wait until it is time to replace them.

Thanks for the compliments on the cars! The Chrysler is a Model 75 Dual Cowl Phaeton. I've been told there are only 13 of them known to still exist. It won national AACA awards in 2000 and 2001. The Packard was reportedly originally owned by William Clark - former MT Senator and copper mine king who Clark County, Nevada is named after.

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As I mentioned before, the switch doesn't really "know" what voltage is passing through it. The switch is designed to break a certain voltage and conduct a certain amperage. As long as your numbers are at or below the switch rating for both, it will work. Which brings us to...

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Yes, that's the intended operation. You may have noticed that the switch is disproportionately small compared to the battery cables that connect to it. They do this by simply making the conductors in the switch somewhat thinner than in the cables. The switch is small so the very short length of the subpar conductor doesn't add much resistance to the circuit. But it will heat up the same as any other resistor. Therefore, it needs time to cool. If you don't let it, the switch could be damaged from overheating, but you will also notice the engine cranking slower as the switch gets hotter, since hotter metals have poorer conductivity. This results in a positive feedback loop, making the switch temperature rise a little faster than proportional to the time that you leave it on at a time.

You shouldn't need to crank for 10 seconds to start one of these cars. If my 55 doesn't start in 1 turn (1.5 seconds), I can already tell there is something wrong. Heck, if it doesn't start in half that time I already know I need to pump the gas again. The obvious exception being to prime the fuel, but it's worth noting that the manufacturers didn't expect you to have to do that all the time. If you drive the car every couple days, it will still have fuel in the lines if not the carb itself. So I'd suggest just priming the carb to get the fuel supply taken care of, then I would hope it would just start right up.

If you only crank in 2-second bursts, doing about 10 of those spaced across 5 minutes would almost certainly be fine, and that's plenty of starting attempts.

How about putting a disconnect switch in the body feed wire and leaving the starter motor circuit intact?

Pgh- I'm still a little fuzzy on what my numbers are. One of the early posts on this thread said to use a 300 amp continuous and 2000 intermittent switch. The Cole Hersee one recommended more recently is quite a bit lower than that. I only know my battery is 640 CCA, so even the 800 amp intermittent would cover that. I think that would be fine, but I'm not sure. As far as cranking goes, I must have some sort of issue with my Chrysler, as it has been taking 4-6 ten seconds cranks to start. The Packard fires up within a few seconds. I'm getting a new set of 00 battery cables to replace the 1 cables there now, so maybe that will help. I was planning to mount this directly on the wood floor just below my feet. Would that create a fire hazard?

TXGoat - I don't quite understand what a body feed wire is, but would love to learn more. I plan to run a cable from the ground post to the switch and another from the switch to the positive terminal.

As I posted just the other day, I have good reason to expect you will be looking at about 200 amps continuous and 700 peak (in this application, peak is at the instant before the engine is turning at speed).

The Chrysler cranking time is normal if it has to pull fuel alllllll the way from the tank by vacuum. (When you go back far enough, the cars would pressurize the tank instead, but same story if it's not primed.) I don't know enough about the fuel system in either to know why the Packard doesn't do that. I can tell you on a 50's car parked for a while, it's basically the same story as your Chrysler.

Whether or not it's a fire hazard is more about the quality of the installation. Cables need a solid connection to not come loose, as well as the switch itself to not short its live terminal against the body.

The body feed wire is the singular wire coming off the starter lug that powers the rest of the car, hence the name (it feeds power to the body).

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You are receiving good advice on this question, but I would find a local expert to install your switch. There is no room for error with high current circuits. Even though you did not mean it, you described a short circuit.

As far as intermittent operation, I think you will find the starter motor also has a recommendation of not to exceed a certain number of seconds of on time when starting the engine. This number varies by starter brand and is particularly true of the starters which use a large pinion shift solenoid. In those solenoids the coils can overheat and cause the plastic or bakelite core the wire coil is wrapped around to expand in size or otherwise distort. A severe enough distortion and the plunger can seize in the core when it is pulled in. Pgh Ultra explained why the switch has a similar intermittent rating because heat in the smaller conductor inside the switch which moves and makes the connection can cause the plastic part it is mounted on to distort too.

As to why I recommended a switch with a fairly high rating, it is a pure case of worst case scenario. 6v starter motors have a normal cranking amp draw of somewhere between 200-350 amps presuming all is well and the engine is turning freely -- the looser the engine the lower the number up to a point. A stiff engine but still free turning such as a new rebuild will be pulling a bit higher. The need for higher switch ratings comes when the engine cannot turn for some reason. Packard was a bit lax in publishing starter motor specs but what I did find in prewar manuals we have on site lists a stall amp draw of 475 ams for a small 6 cylinder starter and as high as 810 amps for a large super 8 or 12 starter. Stall amps means the motor is not turning and this means it is pulling a considerable amount of current so when it comes to a switch you really want a comfortable fudge factor above the worst case scenario.

While conceivably a 1000 amp rating would work the old school of thought was you should have a fudge factor of twice the highest expected worst case scenario. In the case of a direct short such as if a cable shorted to the frame it is also good to have extra but if a cable shorted and stayed connected for very long without melting I doubt any switch or even the battery or cable would survive. A rating of 2000 amps fits comfortably in the worst case and is a commonly available switch. If you had a 12v car then typically amp draw is roughly half that of the 6v car and you could get by comfortably with a smaller rated switch.

You asked if the 500 amp at 12v switch would work and it will not if the starter should stall and start pulling anything over 500 amps like the worst case 810 amps. Even though it has a 5000 amp instantaneous rating that is typically only for a surge of a few milliseconds when the load starts and not sustained like if a motor stalled or was pulling a few seconds worth of heavy current trying to move a stiff engine.