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12 volt positive ground conversion

Discussion in 'The Hokey Ass Message Board' started by spiders web, Aug 19, 2012.

  1. spiders web
    Joined: Jan 16, 2011
    Posts: 384

    spiders web
    Member

    Hey guys. Any body change a 12 pos ground to a 12 neg ground? Lights are not a problem but what about the dash guages? Do I have to send them in for a high dollar transformation or can this be accomplished with relative ease. I hate electrical and this is over my head. Help please.
     
  2. wood470
    Joined: May 21, 2008
    Posts: 226

    wood470
    Member

    What has a positive ground 12 volts, and why change it?
     
  3. Mr 42
    Joined: Mar 27, 2003
    Posts: 1,216

    Mr 42
    Member
    from Sweden

    All gauges will work, except the amp gauge the will show backwards.
    so switch the connections.

    Defroster fan will go backwards and maybe the wiper motor to.
     
  4. Lots of old Brit cars are 12V positive ground. Usually they are switched so modern radios can be installed. You have to switch the ammeter wires, the coil wires and re polarize the generator, if it has one. Motors will all turn in the correct direction.
     

  5. spiders web
    Joined: Jan 16, 2011
    Posts: 384

    spiders web
    Member

    Thanks guys but will the motors like the wiper motor be ok if I just reverse the wires? Oh and by the way its American.
     
  6. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,392

    Mr48chev
    ALLIANCE MEMBER

    Carl is correct on what you need to do to make the change. I'm curious as to what make year and model of car this is as in close to 50 years of working on cars I've never run into an 12V American made car that was positive ground that I can recall.
     
  7. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    tommy
    Member Emeritus

    An American what?????
     
  8. Nash Metropolitians are 12volt positive ground.
     
  9. Metros are British
     
  10. Not the Nash ones.
     
  11. Quit playing games and tell us what kind of car it is and you will get a better answer. Is it just a late Ford that someone changed to positive ground or what?

    Charlie Stephens
     
  12. made from british parts, yes. But sold by an American car company.
     
  13. And designed by American company. Early out sourcing.
     
  14. Better do some homework. All Metropolitans were built by the Austin division of BMC. Virtually every part on the cars were British sourced. They may have used American tires and headlamps
     
  15. Or hold a mirror up to it so it reads right!

    Bob
     
  16. I'm still curious as to which American car was 12V positive ground.
     
  17. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    1955 Packard and Clippers were 12V Positive Ground.
     
  18. Bingo - and he says he has "several Packards"
     
  19. Your fuel gage will not work properly but temp gage will be fine. There are a couple ways around this. One is to rewire the fuel gage and the other is to isolate the sending unit from the tank with Nylon screws as the sending unit can't be converted. I also highly reccomend going to a single wire GM alternator and eliminating the ext. regulator (Lucas I believe). No worries about the fan, starter motor or lights. Later tonight I'll try to send you more specific instructions as I have done this with some non-US cars That I work with often.
     
  20. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,392

    Mr48chev
    ALLIANCE MEMBER

    Ok and that is one car that I have never worked on.
     
  21. I really doubt that Packard used Lucas regulators.
    Also, though I am no electrical genius, The sending unit is nothing more than a potentiometer. It is not negative or positive any more than an on/off switch is.
    Single wire alternators can have their own set of problems. There are very compelling reasons why no car manufacturer has ever used one.
    Just follow the procedures that have been given, previously, and there will be no problems switching polarity
     
  22. spiders web
    Joined: Jan 16, 2011
    Posts: 384

    spiders web
    Member

    Tell them Johnny what they have won!!!!!!!!!!!!! All packards were positive ground form inception through 1955. They went to Neg ground in 56. I believe Studes were Pos ground for a while but not sure. Also for mr. adjustablejohnson the Nash metro is british ( I have a 57). The engine is made by Austin and the electric is lucas (getting tossed and rewired) . Hey thanks guys for all the help, I really think it will help.
     
    Last edited: Aug 21, 2012
  23. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,146

    d2_willys
    Member
    from Kansas

    I changed my 65 MGB over from +GND to -GND (12V) years ago. Did this due to the Lucas generator and regulator constantly were going bad. So I went with an early Delcotron (10si weren't around yet) and external regulator. Believe it, the conversion was easy, and the gas gauge worked just fine as is. Temp and Oil are mechanical. No ammeter originally, just an idiot light, that I used a simple 12v relay to take the idiot light output from regulator and invert the signal. Everything else was unchanged. However I did get to lose the radio inverter box and wire the radio straight up.

    The gauges might just work for you, as the balancing coil types that GM uses are just electromagnets. The Ford gauges are bi metal strip types and shouldn't be polarity sensitive.
     
  24. 62rebel
    Joined: Sep 1, 2008
    Posts: 2,816

    62rebel
    Member

    okay, we sorted that out... now: how do i correctly work the wiring so my '51 Ford instruments (stock) work with 12v negative ground?
     
  25. 62rebel
    Joined: Sep 1, 2008
    Posts: 2,816

    62rebel
    Member

    that's the simplest method i've ever seen explained. and CHEAP, as well. thanks!
     
  26. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,146

    d2_willys
    Member
    from Kansas

    If it already doesn't work with your present FURD instrument voltage regulator, then get one from a 56 up Furd and replace your present one. The outputs of both IVRs are 5 volts or so. Easier done then said!
     
  27. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,392

    Mr48chev
    ALLIANCE MEMBER

    I just woke up last night and remembered that the 55 Metropolitan ragtop I had in my sr year of high school came with 12V pos ground. When the Lucas generator crapped out we swapped in a late 50's Chevy generator and regulator and changed it to Neg ground. the only change we made to the car was swapping the wires on the amp gauge.

    The guy I traded the car to threw the generator away and put a Lucas back on the car after he hooked the battery back up pos ground when he put the engine out of his wrecked Metro in it and the needle went to - all the time.
     

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