Changing out electrical system on my 55 Desoto?

if you want to go down that road, bear in mind that you'll be changing from a 6V positive ground to a 12V negative ground. You'll have to replace some of the gauges with 12V gauges from a 56 Desoto, which have a different background. Also pretty much anything electrical needs to be changed over (radio, power windows, power seat, etc).

My preference, and what I'm doing with my 55, is to leave it as a 6V system. But due to the fact that all the wiring is cloth-type and a lot of it is frayed, I redid the entire harness. So now the car should start easily. it's important that the battery cables be thicker 0/1 gauge.

Ron

Upon further looking into the project, i was figuring finding a good 6v battery ight be difficult, but thats just simply not the case. finding that they are readily available, including a relatively inexpensive optima 6v is available . im thinking your route is probably the best way to go.

Yeah, I was amazed to find that our local NAPA had one right on the shelf. I was also able to find all of the 6V light bulbs locally.

Ron

My preference, and what I'm doing with my 55, is to leave it as a 6V system. But due to the fact that all the wiring is cloth-type and a lot of it is frayed, I redid the entire harness. So now the car should start easily. it's important that the battery cables be thicker 0/1 gauge.

Ron

Ron, so you "redid the entire harness" eh? Does that mean you replaced it with a new harness or replaced it wire by wire? And how much work was involved?

My '55 wiring looks horrible and sooner or later at least bits and pieces of it will surely need to be replaced. Are replacement harnesses available? NOS? Aftermarket? Can it be done piecemeal? Or is that liable to introduce new problems?

The wiring is a "when I get around to it" issue. Right now it is brakes. I took it for a test drive today. All I can say is it is a good thing I have some experience sailing! I was able to turn it into the wind and get it in irons.

Michael -

The entire harness was removed from the car. Every wire was labeled as to where it connected. The shop manual has a schematic that you can work with. I replaced every wire with it's equivalent in gauge and color, but using modern vinyl covered wire. It's an ambitious job. But I did a little every night after work. Took about a month. The alternative is risking a fire if one of the bare wires touches a ground. Also: Rhode Island Wiring and Y n Z Automotive make up entire 55 Desoto harnesses, which, I understand, are excellent quality. Expensive though.

Brakes: You need an Ammco 1750 tool, or your brakes will never work correctly. There is a guy in the club, Rich Hartung, who rents out his 1750 for a fee.

Ron

Michael -

The entire harness was removed from the car. Every wire was labeled as to where it connected. The shop manual has a schematic that you can work with. I replaced every wire with it's equivalent in gauge and color, but using modern vinyl covered wire. It's an ambitious job. But I did a little every night after work. Took about a month. The alternative is risking a fire if one of the bare wires touches a ground. Also: Rhode Island Wiring and Y n Z Automotive make up entire 55 Desoto harnesses, which, I understand, are excellent quality. Expensive though.

Brakes: You need an Ammco 1750 tool, or your brakes will never work correctly. There is a guy in the club, Rich Hartung, who rents out his 1750 for a fee.

Ron

Thanks Ron, so it guess the re-wiring would be a winter project
I found a couple of forums about building a home made replacement for a 1750. One was using a maple block mounted on the spindle and just a threaded rod from it to another scrap of wood to serve as the caliper end. But other info is talking about 0.06" and 0.002" clearances (I may have too many zeros or have them in the wrong positions. I don't have the numbers in front of me now) and I have a hard time seeing anything built from wood and coarse-threaded rod approaching that kind of precision. Maybe I'll check with Rich Hartung if he'll rent that tool out into Canada. Last I spoke with Russ (my mechanic) he was going to check whether the shoes hard gone hard and maybe try sanding them.

The procedure I read about (given I didn't have pictures and don't have any auto repair experience) sounded fairly straight forward: check both drums and shoes have the same arc, adjust the main cam/pivots to correct clearance, then the minor adjustment cams and check with the tool (essentially specialized calipers with a precision dial) that the clearance is correct all around. It seems to me if the arcs are identical and the clearance is correct at each end it should be good all round. I'm just not so good with geometry that I can visualize the shoe PIVOTING on a fixed point and still meeting the drum all along the shoe surface. Obviously the pivot is offset somehow but I just can't visualize it clearly. That's why I have Russ working on it instead of trying to do it myself with the car jacked up in the driveway.

Posted by: @ryanharris

Ok, to start this out, I know NOTHING about Desotos, so please bear this in mind. I have 20 + years Mechanical experience , so im by no means a novice. I have several 70's A-body Mopars, that I have done pretty much anything you can imagine on ....LOL. My understanding of the 55 Desotos I have , is that they run off a 6v electric system. If that is the case, what is involved in swapping to a more modern 12 v system? Is it even a reasonable undertaking? Never had any experience with a 6v system AT ALL. Any advice, or point me to a good article or.....?? Thank you .

Hey Ryan, just purchased a 55 Firedome S22 wagon. Wiring is chopped to pieces, so I am stepping up to a 12 vlt system.  I will probably go with a YnZ's yesterdays parts harness complete.  To start with, you might want to purchase Randy Rundle's "The Official 12-volt Conversion Guide" booklet. Some good info in there that you can use.  Since my existing wiring system is so bad, and it all needs replacing, I am opting for reliability over "diehardness" - so to speak.  Good luck,  John

Hey John and Ryan,

I recently purchased a ‘55 Fireflite which had already been converted over to 12v, and I’ve been left with a hodge-podge of wiring and many ongoing questions. For instance, I discovered only one set of points in my dual point distributor. Could this have anything to do with the conversion? Also have no backup lights and suspect the backup switch. Again, could the conversion be the problem, or do I just need a new switch (which I can’t find BTW). My gas gage also doesn’t work.

My advice to anyone contemplating a conversion to 12v: don’t do it!

Roger Hubbs

@rogerhubbs.  Hey Roger, Distributor will work fine with one set of points. It will just shorten the dwell time to the coil. Nothing to do with the conversion. No back up lights - install a 12 volt back up light switch.  Fuel gauge - If the gauge isn't cooked already, you need to install a "runtz"  voltage reducer in the gauge circuit.

@john-cailey

Hi John,

Thanks for the tips! I need all I can get.

Any idea where I might find a 12v backup switch that fits the Powerflite? Also, I suspect the fuel gauge is fried, but can certainly try your suggestion. Where might I get my hands on a runtz reducer?

Best Regards,

Roger

The  backup switch is a pressure switch that wouldn’t be voltage sensitive.  With 12 volts being half the amps of a 6 volt circuit, the original  6 volt backup switch is more than capable.  The Master Parts Manual has one switch for all 55/56 Dodge, Ply, DeS, Chy with the powerflite.  Part number 1603328.  A search on O'Reilly's website calls for a couple different interchanges.  The difference appears to be the pin configuration. 

AC Delco   ACD U855

Standard SLS25 or SLS27

Not to say that your current switch still isn't the problem. It's just a spring loaded ball that responds to hydraulic pressure and closes the circuit when the pressure moves the ball against the spring tension. 

@timbowers

Hi Tim,

I checked the switch for continuity with the engine running and in reverse, but there was nothing. So I’m assuming a new switch will take me there. This is a big help!

Thanks,

Roger

That's the conclusion I would come to!  Looking forward to a good report.

I think you have successfully identified a problematic switch.  The other confirmation you want with the key "on" is that voltage is going into one side of the switch.  That being said, you could take the two wire ends that connect to the switch and connect them and your back up lights should come on with the key "on".  That would help determine the condition of the wiring after the switch and back to and including the bulbs.

So, the backup switch I ordered worked for about a month and then stuck in the on position. That was a standard, so I ordered the delco switch and it has been working for about a week now. The Standard switch looked gummed-up so I soaked it kerosene and set it aside in case the delco fails in future. Could it be time to drain/change my tranny fluid?