Positive Earth to Negative earth 12v

[57Royal]

I have a 57 Aussie Chrysler Royal which is based on the 1953 Plymouth Cranbrook chassis and body.

 

The electrical system is 12v Positive earth.

 

I want to change it over to 12v Negative earth and adapt something like a single wire Alternator to run on the 251 flathead 6 engine.

 

What has to be changed to achieve this?

I ran a search on the forums and came up dry.

 

 

The distributor in the Aussie cars was a Lucas DM6A whereas I think the USA built cars ran a different system?

 

I will be rewiring the vehicle myself with a 12 or 14 circuit harness kit.

 

Picture isn't my car, but same model.

[Don Coatney]

As you are already 12 volts a few changes should be reversal of the polarity on the ignition coil and swapping the wires on your amp gauge assuming your car is equipped with an amp gauge. Does your car have electric wipers? If so you may need to replace the wiper motor and the heater fan motor with a 12 volt negative fan motor. But that will be required only if these motors have a permanent field magnet. If your car has a radio that may present a problem too.

 

I am using a GM single wire alternator. Others may recommend something different so the choice is up to you. Pictured is how I made an alternator bracket using the generator bracket as a starting point on my 251 engine.

 

 

 

 

[57Royal]

Thanks for the information Don. 

 

I hadn't considered the wiper motors. 

 

I will be starting the engine initially with positive earth which should be within the next few weeks.

I work at an auto parts store and have ordered the distributor cap, rotor and points. As well as a carby kit and some wiring.

 

Have an issue with the distributor shaft turning by hand while bolted into the engine.

I have two spares so I will pull this one and fit one of the others and see if the problem persists.

 

There is no evidence of a heater on this car as the dash has no air vents and no outlets on the motor for a heater core.

 

Only vent is in front of the windscreen on the cowl which is lever operated.

 

What about the starter motor ?

Can I just connect it up to the other terminal on the battery once I have converted to neg earth?

 

And I was wondering about things like dash lights and the three speed overdrive transmission.

(Not sure if that is electronically operated or not)

[Don Coatney]

Is there a reason you want to switch to negative ground?

[57Royal]

I guess I am much more comfortable running everything negative earth.

 

I guess I am being lazy.

I just think it would be simpler to run it that way.

 

I plan to get the car restored enough to make the 454km journey to my states capital city for car club runs.

So eventually will be adding a stereo and air conditioning for the long drive. As well as a heater of some sort.

 

I just think it would be easier to locate and fit negative earth equipment.

[TodFitch]

I am not sure of the chronology, but I don't think that strong rare earth magnets were available in 1957. So it is highly likely that all the motors in your car (heater, wiper, and definitely starter) use wire wound field coils and are insensitive to polarity.

 

Other than a radio (no clue if those old tube radios are polarity sensitive), swapping the ammeter leads and coil terminals should be all you need.

 

You can run with the ammeter and coil polarity backwards for a short while, so an easy test would be to swap the battery leads, flash the generator field, and try things out.

[57Royal]

Great news.
Thanks
 
This is a picture of the wiper motor on these cars if it helps:

[57Royal]

Also there is no ammeter on this car from factory.

I plan to put one on but only when it is much closer to completion.

 

Here is the dash on the car:

 

 

 

So Speedo, Fuel and Temp gauges and idiot lights for oil pressure and generator.

Edited February 22, 2014 by 57Royal

[57Royal]

Also I forgot to mention, but the only wires left on the engine are the wires from the starter to the battery tray with a solenoid and a couple of wires on the distributor which I dont think go anywhere.

 

The previous owner had no idea and cut the harness from the engine bay.

 

I have a workshop manual on CD, but it isn't a very good scan so its hard to read some parts.

 

Just trying to figure out what has to be hooked up to make it run.

 

I have no idea on the state of the engine except that it turns over by hand on the fan belt with some effort.

Edited February 22, 2014 by 57Royal

[57Royal]

By the way, thanks Don Coatney for the pictures of your alternator swap. 

 

Excellent work.

I may have to do the same type of setup for mine and those pictures will come in very handy.

 

Thanks.

[Don Coatney]

Thanks for the information Don. 

 

 

Have an issue with the distributor shaft turning by hand while bolted into the engine.

I have two spares so I will pull this one and fit one of the others and see if the problem persists.

 

Are you sure the distributor is fully seated into the engine block? On my 251 engine the crankshaft must be at TDC in order to remove and install the distributor. Easy way to check if it is seated is to inspect the bolt down plate to make sure it is flat to the raised portion of the engine block as seen in the pictures below. Another thing to check is the rotor to make sure it is keyed correctly to the distributor shaft.

 

There is no evidence of a heater on this car as the dash has no air vents and no outlets on the motor for a heater core.

 

The heater core on your car may be located inside the duct work under the hood (bonnet) of your car. On left hand drive cars this would be on the passenger side. Not sure what side it would be on in a right hand drive car.