'71 RL700L charging issues

[Tomb8764]

Long story short, my truck charges fine on the right bank of batteries (2 6 volt).   But the left bank (2 6 volt) only maintains at 12 volts, never reads anything higher than that when running.  I do have to jump the left side from time to time to get started. Also a bonus, whenever you run any accessories, such as headlights or heater, you get a voltage drop on the left bank.   The right bank stays fine and always charges as it should.   Any thoughts?  

[mowerman]

i used to run one 62 F model..it did not have a push button.everything on the key switch....i was also thinking possibly dead cell in one of the batteries.of coarse non charging side good luck  bob...

[JoeH]

Our '79 used to run on 4 - 6volt batteries, 2 in series on each side, and each side in parallel to each other, yielding 12 volts... Now we just run 3 - 12 volt batteries as they're easier to come by.  Thank God I've never had to deal with a 12/24volt system.

[doubleclutchinweasel]

I guess one important thing to determine on this one is IF it has the 24V system.  If it does, the S/P switch would be suspect.  If it doesn't I would look at the cables.

[cpgeneration]

maybe look at the starter tag ??

[mowerman]

Yes as DCW says it could be as little as corrosion between the cable and the end doesn’t take much sometimes to lose connection as I mentioned I’m sure it’s a small fix .Bob 

[mechohaulic]

look for the obvious first. tracing the cables not only looks for a problem but can also be a learning experience to see what makes the truck run . either way, hope there is a follow-up to let the members here know the end results. was a response given as to the unit having a generator or alternator ?

[Tomb8764]

Ok, that was a lot of information to read through.   I will be checking all battery connections when my weekend roles in on Wednesday.    I will also check out that s/p switch that may be under the metal console in between the seats.   I will add in that this truck is not a push button start, it's got a regular key start which looks original .   Keep the ideas rolling in, I appreciate all the input!

[mechohaulic]

If there is a S/P switch on your unit, doubt it is between seats (more in B models). unit has one ; which i'm starting to think not it will be in the battery box.  quick look at the cables will tell if a S/p is there. cables are short going from battery box  to frame for ground it's 12 v. what yr is truck ,is it alt or gen?

[mechohaulic]

Just now, mechohaulic said:

If there is a S/P switch on your unit, doubt it is between seats (more in B models). unit has one ; which i'm starting to think not it will be in the battery box.  quick look at the cables will tell if a S/p is there. cables are short going from battery box  to frame for ground it's 12 v. what yr is truck ,is it alt or gen?

got the yr '71 see it in topic title , could be alt or gen. i question power source only due to a gen will make its own  power an alt needs power to make power. 

[h67st]

When I worked at Cat we had a "start cart" which was 4 batteries with heavy jumper cables and you could select 6, 12, or 24 volts. When it was cold outside and a 12v truck was turning over lazy, switching to 24v would really get it spinning!

[Tomb8764]

I finally talked to my local mack service shop and got some great information.    I got a wiring diagram for the starting system which was super helpful.   And a phone# to some folks that can probably provide me with a wiring schematic for the whole truck.   Replaced nearly all the battery cables and that helped out a lot.   I may need to replace the series parallel switch to get the charging system working better.   Anyway just giving an update, thanks for all the advice!

[mechohaulic]

updates are always appreciated . lets folks know their input  is being used. the lower picture has the hash mark i would assume that's your system. before purchase of SP switch, if cable replace /cleaning is an improvement; i would say continue with the cleaning cable ends first. with many parts i had , a brand new  SP switch was thrown out yrs ago = thinking no one uses these . such a mistake. bad as that sounds; you would be sick if I listed the truck load of DD parts i had that went over the bank. brand new complete liner kits etc . updates are good

[Tomb8764]

I just ordered a new s/p switch, pretty sure that is my charging problem(only half the batteries getting a charge).   Hopefully going to be able to start hauling soon, maybe even make some money!