From what I gather it was pretty much arbitrary, one of the theories around when I had one of these auto's was it was to reduce galvanic corrosion at chassis termination points.
Max.

 

This is getting interesting... do you know of any specific case in the "other systems" category that has done this? Also, is there a specific reason why this could be an advantage over the standard negative ground?

A lot of tractors and work machines were positive ground.

In general, when you have two metals that are electrically active (either as part of an electrical system or just as part of a passive unintentional cell) you will get more corrosion on the anode than on the cathode. This is the whole idea of sacrificial anodes in hot water heaters and on the hulls of ships. This is why one battery terminal connector corrodes much more than the other. On a vehicle that is using the frame and body as an electrical contact, you will tend to get more corrosion on the electrical wires with a positive ground and more corrosion on the frame/chassis with a negative ground. Electrical connections tend to fail quicker when the wires corrode than when the frame corrodes, so a positive ground can make for less frequent maintenance. But we have gotten pretty good at protecting wires and electrical connections and it is harder to protect the frame and chassis, so a negative ground can make for a frame/chassis that last longer.

 

Why? Lots of cars (and other systems) have used a positive ground convention.

Quite common in portable radios back when NPN transistors were comaratively rare.

 

How did you connect them?

Oh, well- I didn't keep the circuit on the breadboard as my fun of verifying was successful.I did connect Vdd to power , Vss to neutral/GND(whatever one be called it- as long the right meaning is conveyed- I hope so))the decoder , four decoders outputs to four LEDS with required resistances controlled by four PNP transistors and a sketch.The simple sketch is given below:

const int INput1 =  11;
const int INput2 =  12;
void setup() {
  // put your setup code here, to run once:
pinMode(INput1,OUTPUT);
pinMode(INput2,OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(INput1,HIGH);digitalWrite(INput2,HIGH);
  delay(1000);
  digitalWrite(INput1,HIGH);digitalWrite(INput2,LOW);
  delay(1000);
  digitalWrite(INput1,LOW);digitalWrite(INput2,HIGH);
  delay(1000);
  digitalWrite(INput1,LOW);digitalWrite(INput2,LOW);
  delay(1000);
}

All four except one was lighted and the one that wasn't lighted kept chagning every second.
sureshparanjape

Moderators note: Please use code tags for pieces of code

 

What does this code have to do with connecting four NAND gates together?

 

What does this code have to do with connecting four NAND gates together?

I used 4 NAND gates from an IC to get 2 to 4 decoder and used two inputs to get four outputs.
sureshparanjape

 

I used 4 NAND gates from an IC to get 2 to 4 decoder and used two inputs to get four outputs.
sureshparanjape

Excellent and congratulations. Back when I was experimenting like this I had to use slide switches to make the inputs. Oh how things have changed.

What does this code have to do with connecting four NAND gates together?

I suggest you go back and read the very first post of this thread. Sureshparanjape (you know, the thread starter?) started the thread by stating he was using an Arduino as the digital signal source.