61 Mack Posted June 3 Share Posted June 3 I have a 1962 Mack. No batteries in unit. Cables are not color coded. How do i determine if vehicle is positive or negative ground? Quote Link to comment https://www.bigmacktrucks.com/topic/74220-positive-or-negative-ground/ Share on other sites More sharing options...
Popular Post Geoff Weeks Posted June 3 Popular Post Share Posted June 3 several ways to make an educated guess. 1) if the engine has an alternator and not a generator look to see what polarity is grounded, Alternator care about polarity so should be marked. 2) if a generator the regulator may be marked as to polarity 3) if the truck has an ammeter and no alternator, disconnect any radios and electronics and hook up a battery and turn on as many lights as possible and see if the ammeter points to - or +. If negative, then you have the right polarity, if it points toward + you have it backwards. If the vehicle has an alternator, disconnect all wires before doing this test. 4) look at the terminal ends at the battery, larger terminal goes to +, the one with the smaller hole is - (this is for old post type batteries.) Since old trucks with generators and no radios they will not care and can be switched at will. 3 Quote Link to comment https://www.bigmacktrucks.com/topic/74220-positive-or-negative-ground/#findComment-553043 Share on other sites More sharing options...
Swishy Posted June 5 Share Posted June 5 (edited) Many moons ago we had a 1978 Mack with positive ground it was a PIA ... mainly with our 2 way radio system (old valve Sets) ran seperated wires from battery with reverse polarity (negative to 2 way radio earh) lucky the 2Way was mounted on a fibre glass cab the reason they told us why positve earth was to try and stop battery terminals from corroding ....... Not sure if it worked as we had air start etc What Sez U? cya Edited June 5 by Swishy Quote Link to comment https://www.bigmacktrucks.com/topic/74220-positive-or-negative-ground/#findComment-553117 Share on other sites More sharing options...
h67st Posted June 5 Share Posted June 5 2 hours ago, Swishy said: Many moons ago we had a 1978 Mack with positive ground it was a PIA ... mainly with our 2 way radio system (old valve Sets) ran seperated wires from battery with reverse polarity (negative to 2 way radio earh) lucky the 2Way was mounted on a fibre glass cab the reason they told us why positve earth was to try and stop battery terminals from corroding ....... Not sure if it worked as we had air start etc What Sez U? I did a little internet search and the consensus seems to agree with you-less corrosion in a positive ground system due to the direction the electrons flow. Quote Link to comment https://www.bigmacktrucks.com/topic/74220-positive-or-negative-ground/#findComment-553122 Share on other sites More sharing options...
Geoff Weeks Posted June 5 Share Posted June 5 I've heard that alot, but it has always been by non technical people. I haven't heard any conclusive proof. There are many reasons why I doubt the "corrosion" explanation. My Uncle was a corrosion specialist for USS and I wish I had thought to put the question to him when he was alive. 1) most corrosion is caused by air and moisture/salts external to the wiring, new sealed lights more or less prove the point, now the corrosion is not at the light bulb but at the connection, again where air and moisture can attack it. 2) we still have as many connections with either polarity and while the direction of flow at each connection is reversed you still have steel to copper, so if it would make a difference it would just move the corrosion point not eliminate it. 3) some point to galvanic protection of pipeline and bridge structures as proof, this misses the point that vehicles move through the air and to be effective you would have to charge the air around the vehicle to have any effect. 4) when positive ground was popular, little was known of galvanic corrosion or the effect or direction of electron flow in a dc circuit. With old simple vehicles, it just plain didn't matter, most gauges didn't care (later balanced coils gauges do) so it really didn't matter which way around the vehicle was. In the 6 volt era, you saw a lot of positive ground. When the switch to 12 volt as the common vehicle voltage is when we see negative ground become popular. It think it was more to differentiate from the 6 volt vehicles. Once semi-conductors started being used, it cemented negative ground. For some reason it is cheaper and easier to mfg semi conductors in that polarity. Old tube radios used vibrator coils to make a static inverter essentially isolating the radio power feed from the vehicle. I had an old Telafunken (sp?) out of a '55 Porsche that could be run on both 6 or 12 volt, positive or negative ground. Once transistor radios came in most were negative ground. An alternator requires diode in both polarities so no gain or loss there as to vehicle polarity. L/N an early maker of automotive alternators, went with "case neutral" construction so could be used on either polarity, most other mfg made the case one polarity or the other, requiring a different part number for + or - ground. With the abundance of semi-conductors in a modern vehicle, negative ground is almost taken over. You did ask Swishy. Quote Link to comment https://www.bigmacktrucks.com/topic/74220-positive-or-negative-ground/#findComment-553124 Share on other sites More sharing options...
mechohaulic Posted June 5 Share Posted June 5 '62 ??? Mack ( B model ?) . on occasion knowing the model number helps. one battery box or two? I say two. box big enough for two 6 volt in series {== 12 volt} ? series parallel switch ? I go with the idea of checking cable terminal ends in box(es). even two sixes with jumper still only have two out cables Quote Link to comment https://www.bigmacktrucks.com/topic/74220-positive-or-negative-ground/#findComment-553134 Share on other sites More sharing options...
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