Positive to negative ground

[70mackMB]

So we are thinking of going to negative ground on the (1970) MB. What would be the best short or long version to accomplish this? Thank you for your time and info.   .....Hippy

[eddeere]

This  was discussed a few times here . If I remember correctly switch the wires on the fuel gauge , amp or volt meter , switch the battery cables and polarize the generator . If I left anything out some one here will add to it.

 

 

 

Edited September 3, 2018 by eddeere
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[ws721]

Swap the wires in heater fan. Did that swap to a DM plow truck once. Froze my butt off next storm. Blower motor going full tilt.  But in reverse.

[Hobert62]

If your changing I'd put an alternator on right away too.  Much better charging for your elog.     

[terry]

3 hours ago, Hobert62 said:

If your changing I'd put an alternator on right away too.  Much better charging for your elog.     

Don't think you have to run elog on that old of a truck.     terry

[70mackMB]

6 hours ago, Hobert62 said:

If your changing I'd put an alternator on right away too.  Much better charging for your elog.     

It doesn't go fast enough to activate an elog into motion mode!

Thanks everyone for commenting   .....Hippy

[tenfive0]

What is the advantage on non-advantage of Positive Ground? I'm a retired Firefighter and I started my career hanging on to a grab rail riding the tailboard of CF-600. I have a 1972 CF-600 that has been converted to a Tilt Bed Ramp Truck. I'm perplexed in which direction to head in with fixing some of its wiring issues that I inherited with the truck. It has a four (4) 12 volt batteries, two (2) Parallel Switches and Cole Hersee switch. Originally from the factory the truck had four (4) 6 volt batteries. Someone has been doing some creative thinking and rewiring. I have a wiring schematic that I got form the Mack Museum sent to me via email that I need to study. I'm local to Allentown, PA and I'm not proficient with the computer. I'm going to revisit the Museum to pick up a hard copy of the schematic.

Before I bought the truck it was having an issue with starting. The previous owner was banging on the Parallel Switches with a rubber mallet and he broke both Switches. He had someone wire the starter directly eliminating the Switches. I have to do some tracing and rewiring but I’m not sure which way to head. Should I eliminate the Parallel Switches all together? Should I switch the entire system to negative ground? I’m planning on adding a 12,000 pound electric winch to the bed to assist loading vehicles and equipment. It would be nice to have or keep two (2) banks of 12 volt batteries. I like to do what I can to have durability and reliability.

  

[j hancock]

I have heard that there can be less corrosion in the electrical system using a positive grounds.  Never really looked into that bit of trivia.

Worked on both positive and negative ground vehicles and if all the bits are in good shape, both have performed equally well for me.

If I had your truck, I would probably go with 12 volt negative ground and remove the series parallel switches.

[eddeere]

When the switch to neg ground was done for most cars I was told by a mechanic that it was for corrosion . Looking at the batteries on most of my stuff the positive terminals seem to have the most corrosion .

[tenfive0]

I was at the Mack Museum yesterday and I picked up a wiring schematic for my Truck the way it was wired when it left the factory. At this time I'm not sure if the truck is still hooked up positive ground. It might have been changed by a previous owner. Now that I have a schematic I need to do some further investigating. If it is positive ground it will stay that way for now but I have concluded to losing the parallel switches in an effort to simplify things.

Edited September 11, 2018 by tenfive0

[HeavyGunner]

On 9/8/2018 at 7:11 AM, j hancock said:

I have heard that there can be less corrosion in the electrical system using a positive grounds.  Never really looked into that bit of trivia.

Worked on both positive and negative ground vehicles and if all the bits are in good shape, both have performed equally well for me.

If I had your truck, I would probably go with 12 volt negative ground and remove the series parallel switches.

I was visited no with an electrician awhile back and he was telling me about wiring a positive current to underground pipes such as old water pipes, gas and oil pipes. Somehow it slows the corrosion down to almost nothing. Can’t remember for sure how far each positive wire would protect but I remember it was miles. I want to say around 12 but I honestly can’t remember. 

[Freightrain]

You can put a 12v starter in the truck and get rid of the s/p switches.    You'll just need a std Ford starter solenoid to engage the new starter.  I put it in place of my s/p switch, so the starter button worked without moving wires.  Just run two LARGE(like 4/0) cables from batteries to the starter for both POS and NEG connections.  I'm pretty sure the starter is NOT polarity sensitive.  It only turns one way no matter the connection.  

Two 12v batteries should be more then enough for typical starting.  3 wouldn't hurt, 4 is way overkill.  I ran 4 batteries for years, til they got old and needed replaced.  Then I just put 2 in it and have never had an issue.  

[tenfive0]

I bought the truck the way it is. It's obvious someone has been into the wiring screwing around with things. Its short of hob cobbed, mixed matched with a lot of extra wires and bull crap that's not needed for civilian use in my opinion. I had another decommissioned Fire Truck 30 years ago that I stripped enough wires out of to fill a trash can. Like I said I need to do some further investigating to short it all out before moving forward.

The truck has four (4) 12 volt batteries. Only two (2) of the four (4) batteries are currently hooked up. The two (2) batteries in use are hooked up (parallel) negative negative, positive positive. It is a 12 volt system and the parallel switches are broken, bypassed and not hooked up at all. I was contemplating replacing the parallel switches but I'm just going to leave them disconnected and remove them off the truck and not replace or use them at all. The truck starts the way it is the way it is currently wired. I just need to figure out whats up with it all to make it safe, reliable and not overly complicated. 

[tenfive0]

On 9/11/2018 at 2:59 PM, Freightrain said:

You can put a 12v starter in the truck and get rid of the s/p switches.    You'll just need a std Ford starter solenoid to engage the new starter.  I put it in place of my s/p switch, so the starter button worked without moving wires.  Just run two LARGE(like 4/0) cables from batteries to the starter for both POS and NEG connections.  I'm pretty sure the starter is NOT polarity sensitive.  It only turns one way no matter the connection.  

Two 12v batteries should be more then enough for typical starting.  3 wouldn't hurt, 4 is way overkill.  I ran 4 batteries for years, til they got old and needed replaced.  Then I just put 2 in it and have never had an issue.  

I can confirm my truck came from the factory with a 12 volt starter according to the build sheet provided by the Mack Museum. I don't suspect (why) anyone would have changed it to anything other then 12 volts.

When you reference s/p switches do you mean parallel switches? The factory wiring schematic refers to the parallel switches as MAG. SW. If and when I chose to change the electrical system to negative ground would I be correct to assume the starter polarity won't have to be change? 

 

[Hobert62]

Starter doesn't know the diffrence works either + ground or - ground with same rotation.  

[Freightrain]

The series/parallel switch was for 24v starter.  It surely seems odd your truck had (4) 6v batteries but was 12v start?  The series/parallel switch swapped battery leads around for 24v start(4-6v in series), and 12v run(2-6v in series, but then each pair in parallel=12v run/charge).  If you do a little reading on here you will see that was the popular way to get diesels started up through even the 80's.  I don't know exactly when Mack discontinued it(or other manufacturers either)?

 

Typical diagram:

[tenfive0]

From the factory my CF-600 had two (2) parallel switches and four (4) 6 volt batteries and a 12 volt starter. I'm getting the information directly from the build sheet and wiring schematic provided to me for my truck from the Mack Museum. I'm a retired firefighter and I can remember all our CF-600's were all configured with four (4) 6 volt batteries.      

[Freightrain]

(4) 6volts are common, the fact it was 12v start is what is surprising to me.  I'm not up on fire equipment, so maybe this was common to it?

The two parallel switches were needed to make 12v from two sets of 6v batteries.   Unlike a series/parallel switch for 24v start.

[tenfive0]

On 9/11/2018 at 10:26 PM, tenfive0 said:

I bought the truck the way it is. It's obvious someone has been into the wiring screwing around with things. It's sort of hob cobbed, mixed matched with a lot of extra wires and bull crap that's not needed for civilian use in my opinion. I had another decommissioned Fire Truck 30 years ago that I stripped enough wires out of to fill a trash can. Like I said I need to do some further investigating to short it all out before moving forward.

The truck has four (4) 12 volt batteries. Only two (2) of the four (4) batteries are currently hooked up. The two (2) batteries in use are hooked up (parallel) negative negative, positive positive. It is a 12 volt system and the parallel switches are broken, bypassed and not hooked up at all. I was contemplating replacing the parallel switches but I'm just going to leave them disconnected and remove them off the truck and not replace or use them at all. The truck starts the way it is the way it is currently wired. I just need to figure out whats up with it all to make it safe, reliable and not overly complicated. 

Attached (Mack Museum) drawing the way my CF-600 was wired when it left the factory. Someone made changes somewhere along to way before I bought the truck. I don't know who, when or why? I'm all for leaving well enough alone and if it ain't broken don't fix it. I'm not a electrical wizard but I can follow directions and a drawing. The best I can tell from researching and looking at the factory drawling the batteries were originally hooked up in series. I really don't need to know what to call it I just need know what works, should work or did work. Trying to sort it out but its confusing to me. I'm kind of flip flopping back and forth on what to do. I have to come up with a plan and stick to it. I might go back to the way the truck left the factory because at least it worked. if I hook it up back to the drawling I'll have something that is traceable and IT WORKED. I'm sure a lot of thought and engineering by smarter people then me devised a system that worked. I'm not trying to reinvent the wheel. I just want to have a reliable vehicle that I can depend on to start and perform when needed.