1957 B 61 Positive ground to Negative ground.

[Fred Carter]

I’ve read a lot of swaps from Positive ground to negative ground.  One of the first questions that pops up is why?  I own a 57 Mack and am trying to put a 3 car trailer behind it to move my cars from the West Coast back East.  Truck is ready but I can’t just plug my car Trailer to the truck and expect the electric brakes and lights to work. Any help would be great since I was told to drive my B empty and find another vehicle for the job. 

[doubleclutchinweasel]

Light bulbs typically do not care which way the current is flowing.  Not sure the electric brakes would either.  Somebody on here probably has more experience with that than I do, though.

My R was converted to negative ground when I got it.  Basically went to an alternator, and swapped a couple of cables.  All the lights worked fine.  I had to change the ammeter to 2 "two post" model so I could reverse the polarity on it.

I'm sure some honest-to-goodness experts will chime in here and help you out...especially if you add pictures!!!  We love pictures!!!

[Freightrain]

If you would get an air/electric brake controller (like I have) polarity would not be an issue.  It is just an air cyl that moves a wiper over a rheostat.  Polarity is no issue.  It is a Warner 1300-80.  

https://www.etrailer.com/tv-Demo-Warner-Brake-Controller-1300-80.aspx

If you use a new electronic version the issue is the blue brake wire would put 12v positive to the brakes and it would need 12v neg.  Other issue is if you have any LED bulbs, they would not work due to improper polarity.

[doubleclutchinweasel]

You're correct, 'Train.  I had not considered LED bulbs.  I should have said INCANDESCENT bulbs do not care about polarity.

[609albert]

some LED lights will operate on positive ground , to test if they will work  use a 9 volt battery ( we used to call them transitor radio batteries ) and switch the leads . I did it on my 54 Mack fire truck clearence lights

[Freightrain]

Yes, some of the newer LED lights have circuitry built in to make them more user friendly.  

[Fred Carter]

So I’m buying the brake controller and at that point if I connect my 7 way pin to the B-61 there won’t be any problems between the truck positive ground and the take 3 trailer with negative ground with a breakaway box.  Here is the quick story.  Wanted to be a Mack trucker as a kid. Joined the Navy. 31 years later retiring and buying the classics I wanted as a kid and wanting to pull all of them to my retirement home with the B.  Was told that I may have to take the B empty from Washington to Tn.  Hopefully with y’all’s help we can pull this off! That single axle tractor beats me to death empty. Lol

[doubleclutchinweasel]

1 hour ago, Fred Carter said:

So I’m buying the brake controller and at that point if I connect my 7 way pin to the B-61 there won’t be any problems between the truck positive ground and the take 3 trailer with negative ground with a breakaway box.  Here is the quick story.  Wanted to be a Mack trucker as a kid. Joined the Navy. 31 years later retiring and buying the classics I wanted as a kid and wanting to pull all of them to my retirement home with the B.  Was told that I may have to take the B empty from Washington to Tn.  Hopefully with y’all’s help we can pull this off! That single axle tractor beats me to death empty. Lol

There are enough guys on here to help you do pretty much ANYTHING.  I doubt there is too much that SOMEBODY here has not already done.

[Freightrain]

You will have to reverse the battery wiring on the breakaway battery.  If not, you will not like the consequences if you test the breakaway while truck is attached!  I would absolutely make sure that there is a fuse inline with that battery just as a safety.  At least a small plug in circuit breaker.

This will bastardize your trailer so word of warning.  It might be better overall if you switch the truck over to negative ground.  In the old days the trailer you pulled didnt have battery powered brakes so it was not an issue.  Today it's different with pulling small car trailers.

 

Washington state?  Or DC?  Either will be a longgggg trip bobtail in a B model.  I've run my truck for near 20 yrs pulling my 40 ft Haulmark box.  I typically don't bobtail anymore and I have swapped air ride under mine.

[mrsmackpaul]

For the effort it takes and the convenience it will give to me its a no brainer

 

Swapping to negitive ground would without a doubt the way to go, if you want a phone charger, CB, ordinary car radio or any other really common things we use every day to work as they should it is easier to change just one thing, your truck to suit the rest rather than change everything to then only work on your truck

 

So a alternator is the first port of call, quick simple on wire alternator with a built in regulator 

Dunno if you have a amp guage or volt guage, chances are both will have to have there wirers reversed so they still work the correctly otherwise it it will show volts in negitive instead of positive and the amp guage will show its discharging instead of charging 

There wont be a lot more to change that I can think of off the top of my head 

As I said it's much easier to change one thing rather than 20 things

 

Also if you change the trailer etc and have breakdown, no one else can tow your trailer

 

Paul 

[Freightrain]

I hung a one wire alt on my original gen bracket with some simple modifications to the adjustment swing arm.  I ran a big gauge wire right to the batteries.  I removed the amp meter and installed a voltmeter.  That's it.  The starter doesn't care on polarity.  You could then hook to any trailer without problems.  Like Paul said...radio or whatever can be hooked up.

[doubleclutchinweasel]

Mine was changed when I got it.  Like everybody said, it had a 1-wire alternator with integral regulator.  Battery cables swapped to keep the starter running the right direction.  The only issue was the amp meter.  It was a single stud type and was grounded through the body to the dash.  I swapped in a 2-stud model so I could reverse the polarity.  As far as I know, that was it.  All the lights worked.  The fuel gauge didn't work, but i had a hardwood dowel "dipstick" under the seat!

I agree with Paul and Larry...just reverse the polarity on the truck and be done with it.  Not that difficult.

[Fred Carter]

I appreciate everyone’s inputs. I feel like this is gonna work. I didn’t even think about if the trailer has to be towed. 👍

Hopefully my brake controller arrived on Friday.