mackmb212 Posted May 2, 2012 Share Posted May 2, 2012 I have a 63 b81 I just got I was told it is 24 volt positive groundHow can I tell. Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/ Share on other sites More sharing options...
Rob Posted May 2, 2012 Share Posted May 2, 2012 I have a 63 b81 I just got I was told it is 24 volt positive groundHow can I tell.If it has batteries in the truck look at the positive cable from a battery. If positive ground it will run to the starter motor housing. If it has a generator on the engine chances are it is 12 volt positive ground. There should be a large switch, (series parallel) between the seat under a cover. This converts 12VDC, to 24VDC used in starting. Most alternators are negative ground and I don't think any B model were originally built with an alternator unless a fire apparatus.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-117297 Share on other sites More sharing options...
mackmb212 Posted May 3, 2012 Author Share Posted May 3, 2012 Hey thanks for the reply I got the truck to crank and run off Ether for a few seconds after 10 years of sitting Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-117378 Share on other sites More sharing options...
leversole Posted May 3, 2012 Share Posted May 3, 2012 Sure fire way is to take a meter and measure ohms from either cable to a bare sport on the frame...one will have almost no resistance, the is the "ground" whether positve or negative... Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-117397 Share on other sites More sharing options...
twostickmutt Posted May 5, 2012 Share Posted May 5, 2012 i have asked this question for years and got years of different answers. why did different makes of cars and trucks have positive ground and not just negative ground on all? Quote and remember "PREFORMANCE COUNTS" Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-117772 Share on other sites More sharing options...
mackmb212 Posted May 5, 2012 Author Share Posted May 5, 2012 A quick story about positive ground. The fire dept I run with had a 66 American lafrance in the 80s it was in a bad wreck the truck sat around for a year until they decided to rebuild it when it came back from lafrance and had all the equipment put back on it was over the truck gvw and had a positive ground lafrance never told the fire dept about that and as they put the radios and other electronics in they shorted out. They sold the truck in 1991 to a fire dept in the southern states 10 years ago the we got a random phone call asking if we owned this truck and did the pump work because the truck burned up and these people wanted to rebuild it no one ever told the people it was positive ground when they bought it and they started wiring stuff to the truck causing it to burn. Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-117787 Share on other sites More sharing options...
Rob Posted May 5, 2012 Share Posted May 5, 2012 Sure fire way is to take a meter and measure ohms from either cable to a bare sport on the frame...one will have almost no resistance, the is the "ground" whether positve or negative...A lot of meters will pop their fuses if you apply voltage when the ohms scale is selected for a short period.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-117789 Share on other sites More sharing options...
leversole Posted May 5, 2012 Share Posted May 5, 2012 Forgot to mention to take the cable off of the battery!!! A simple 12 volt test lamp will work also, either negative battery terminal to frame or positive battery terminal to frame will make the light light up! Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-117804 Share on other sites More sharing options...
mackmb212 Posted May 9, 2012 Author Share Posted May 9, 2012 I got it straightend out i shoud of looked on the starter it says 12v and where that parallel switch is supposed to be there is a ford looking stater silonied Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-118400 Share on other sites More sharing options...
Trevor Flores Posted April 3, 2018 Share Posted April 3, 2018 Got a positive ground Mac truck in today at my job having a tough time figuring how I can make led lights work on newer gooseneck if possible?! Any help anyone? Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-395779 Share on other sites More sharing options...
41chevy Posted April 3, 2018 Share Posted April 3, 2018 2 minutes ago, Trevor Flores said: Got a positive ground Mac truck in today at my job having a tough time figuring how I can make led lights work on newer gooseneck if possible?! Any help anyone? They make positive ground LED for older British cars and motorcycles. Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-395781 Share on other sites More sharing options...
Trevor Flores Posted April 3, 2018 Share Posted April 3, 2018 Trying to get the guy back to where he’s from with the new trailer but can’t seem to figure out how to override the positive ground 24V system I’ve tried everything I know to get around it and still back at the same spot. Quote Link to comment https://www.bigmacktrucks.com/topic/24888-63-b81-how-can-i-tell-if-its-24v-positive-ground/#findComment-395782 Share on other sites More sharing options...
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