Question about 12-volt negative earth

[LizardsA]

Good day,

I have been asked to work on a friend's Model 'A' that has a 12-volt negative earth conversion. I eagerly ripped out wires because this looked like a terrible "botch" job. I am now in a position to begin rewiring.

My question is: can I rewire this car as per the standard Model 'A' electrical diagram, or do I need to make changes for any reason?

Further questions
1. Will the 6-volt condenser work on a 12-volt set-up?
2. The coil is a 12-volt coil;
3. Do I have to wire the vehicle with a negative earth?
4. Does the wiring change on the amp meter?

I do apologise for the strange questions, but I am a bit of a troglodyte when it comes to vehicle electrics.

Mike

[chap52]

Go to the "Search" tab at the top of this page, click on "Advanced Search" at the bottom of the pop up. Enter "12 volt conversion" in the subject box and highlight "Model A 1928-1931). You will get you a boatload of info on the subject.
This is a good way to access previous posts. I know this subject has been covered many times before. Hope it helps, Chap

[BillLee/Chandler, TX]

Check out http://cedarcreekas.org/TechTopics/1...rn_Signals.pdf

[kd4lok]

Think it might have been best to fix what, if anything, was broke first
before ripping out all the wiring.

[jrelliott]

The wiring is the same for 6V Positive Ground or 12 V Negative Ground with the exception of the 12V coil instead of 6V coil( You can use 6V coil with a dropping resistor). The coil wires are reversed on the coil as are the wires on the amp meter. You just have to change all the bulbs. The condenser in the distributor will work no need to change.
Just hook up the ground of the battery to the frame ground and the positive cable to the starter.

[LizardsA]

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Thanks everyone.

So, jrelliott, it looks like the wiring is the same as the wiring diagram, except for the couple of changes you mentioned?

Kd4lok, the wiring was a mess to start with, nasty "short cuts" and stupidity all over theplace - none of it made any sense! Hence, it was easier just to clip it all off and try and get it back as close to original as possible, as long as there was no complications involved.

[redmodelt]

AS the car has been running 12 volt, just rewire as you would a 6 volt system except as stated above the coil and meter. I understand messed up wiring and sometimes it is safer to pull it all out and start fresh. A few have come into the shop, that was the condition when they came in. The previous owner added wires here and there and some went no where or had spliced in bits here and there to replace tatty wire.
If you don't have a tester, look on line how to check the polarity of the coil. The car will run with the leads reversed but not as well.

[LizardsA]

Redmodelt, the car has a coil with a "+" on one side, and a '-" on the other - I'm sure that will do the trick

[redmodelt]

Should.

[kd4lok]

As part of the wiring update, if not already existing, I Would add a Battery Disconnect switch in the GND cable to the battery.

[LizardsA]

Just to check on the good advice provided above: I keep the wiring the same as if it was a 6-volt positive earth system, but make the following changes:
1. Swop the wires over on the coil;
2. Swop the wires over on the amp meter;
3. Do I need to swop the wires over on the ignition switch?
4. Will there be any change to the wires going to the distributor?

As always, your assistance is most welcome!

Mike
Johannesburg, South Africa

[Patrick L.]

#3. no
#4. Yes. The - primary wire will now go to the points which actually refers to your question
#1.

[LizardsA]

Thamks PatrickL - how does one do this without it looking like another big mess?

[Tom Wesenberg]

You don't need to touch the popout nor the distributor.

[LizardsA]

Tom Wesenberg: if the answer that PartickL gave to my questions:
3. Do I need to swop the wires over on the ignition switch? - "no"
4. Will there be any change to the wires going to the distributor? - "yes"

How will #4 be achieved?

[Patrick L.]

Originally Posted by LizardsA

Tom Wesenberg: if the answer that PartickL gave to my questions:
3. Do I need to swop the wires over on the ignition switch? - "no"
4. Will there be any change to the wires going to the distributor? - "yes"

How will #4 be achieved?

Sorry I wasn't clear. Switching the primary wires on the coil is all thats required. The point I didn't make very clear was that the negative [-] primary coil wire now ends up going to the points.