Generator no charge/ no lights

[6x6XL]

so I just picked up a 1951 GMC M135. the truck was forestry service so it was set up to run 12v lights all around. ive taken the truck out a couple times no issues (short run). then last night while taking it work, the lights began to get dim and I lost the marker lights and dash lights. the gauge ran just above dead. the second we put the jumper cables on, it fired right up. so is the generator dead/dying? could the batteries be too weak to take a charge from the generator? is it possible to use something like a gen 1 dodge cummins alternator in stead of the current generator?

Thank you

 

[The King Machine]

Check your grounds first!

 

[gimpyrobb]

Don't check your grounds first!

Check to see if its a 24v system or 12v.

If the alt/gen is 24v, you need to "feed" it 24v for it to start charging(to excite it).

Posting a pic would be the easiest way for us to tell.

 

[6x6XL]

ill post a pic as soon as I can. the generator unit is still the original unit. when I started it today it was running fine. I was reading about 12v on the battery then it died. the whole truck. no juice, not even enough to turn over the starter. it almost acts like its running off the batteries not the generator. again ill post up some pictures as soon as a get a chance.

thank you

 

[gimpyrobb]

If you only have ONE battery, you need to get a second one. The stock system is 24volts.

 

[USMC 00-08]

I would test the one you have in there. It is probably shorted out inside. Mine had the same problem not long ago.

 

[Warthog]

Before starting any electrical troubleshooting always make sure your batteries are fully charged and loadtested.

If you only have one, you need to make sure how your truck is wired. 12v or 24v. Someone may have left out a battery.

 

[6x6XL]

its been a couple days because of an awesome (not really) early snow storm here as well as loosing 2nd gear in my Dodge/cummins transmission. I went and grabbed 2 new rv/marine heavy duty deep cycle batteries today. I had to do an exhaust system on a dodge/cummins this morning so didn't get a chance to put them in. I work nights so ill have them in the morning and go from there. ill check all the cables too while im in there.

there are 2 batteries in the truck, but one was on its last leg anyway.

I pulled the cover on the box where the generator cables go. I got 12.8 volts on the bottom unit but have never seen those, so not sure if I was testing them right.

What are those coil units called? does anyone know how to properly test them?

Thank you.

 

[gimpyrobb]

Hard to say without seeing what you see. I don't have a 135, so I don't know what should be there, but military systems are fairly simple.

 

[nattieleather]

If you have a stock system with the generator and the thick cable that threads on to it going to a box on the firewall that has two connectors on it, the one for the thick cable and the one with a single wire coming out of it, and the box has like 3 or 4 coils and relays inside of it that is the voltage regulator. Older cars and trucks way back in the day used a generator and voltage regulator they were two separate pieces. If you truck has two batteries wired in series (battery 1 - to ground + to battery 2 -, battery 2 + to system) and you have the original generator and voltage regulator then I would give dollars to donuts that the truck is still 24V.

 

[6x6XL]

These are the old batteries installed. I put the new heavy duty deep cycles in and the charging system came online just fine. the needle on the gauge sat right at the yellow/green line and with a bit of a rev, sat about 2 needle widths into the green. the yellow battery I had in there was weak and old. I don't think it was handling the load. There are two and they are wired in series. I still have the generator that runs into the voltage regulator box.

The truck was a forestry service truck and converted to 12v for the lights. I had to replace the taillight bulb and used a 12v bulb no issues. they had wired in a push/pull switch in the dash and disconnected the "multi-switch" when I test into the switch I get 14v with the truck running

Now the charging is online, but I still don't have lights. I still have the headlights, but no accessory lights (front or rear maker and dash lights). I cant find any fuse to run the lights thought or have found any circuit breakers in the wiring diagram.

Any ideas?

 

[eagle4g63]

Not sure about the lights not working, we'll get back to them......for now there is another issue you will need to address....you put in new batteries because as you noticed one of them went down hill...from the looks of things they didn't "Convert" to 12 volts....what they did was put in a 12 volt "tap".....as you found out, that will kill one of the 2 batteries, with only "tapping" off one of the batteries you make that one work harder than the other, so they get an uneven charge put back on them, causing problems. You can put 24 volt bulbs back into the light sockets and hook the light switch back up to 24 volts and have no problems....or put in a 24-12v converter and have a true 12 volt supply that won't harm your 24 volt system.

Now back to the lights....you can pretty easily trouble shoot your problem with the way they used the light switch they did....it will have a single power "in" point and should have 2 power out points...one for head lights and one for running.......if you feel frogy, you can un-hook the wires, use a test light and find the power wire....put it back, now on the other 2 wires run a temp positive wire to one of them at a time, if the head lights come on than go to the next wire, hook it to a battery and see if the rest of the lights come on, if so than the switch is bad if not than you have a ground problem with the lights.....more than likely.

 

[topo]

I went through this when I bought my m211 in 1986 it had 4 marker lights that where 12 volt . one battery would go bad then the regulator . All 12 volt stuff must be taken off .

 

[6x6XL]

so if they tapped the 12v was the forestry service replacing batteries all the time? I don't mind hooking all the 24v back in but would like a 12v system to run lights later as I plan the light this thing up like the moon later and be able to hide things like chargers sockets under the dash.

 

[6x6XL]

also. ive shot the switch with the multi-meter a couple times to be sure, but I have only one hot wire in and it comes off the battery to the switch, but all the others appear to be grounds. any ideas on that?

ill have to re-wire the cannon plug for the multi-switch which isn't a huge deal (I work on B-1's) but were is a good source for 24v bulbs?

The forestry service cut all the wires off the cannon plug, but I do have an extra "factory" switch.

Thank you all for your help!

 

[6x6XL]

Where would be a good place to tap in a power converter?

is there any good guides for converting the entire truck to 12v?

This is my first truck of this nature so its all a learning process for me. I love the truck just need to work out a couple issues here.

 

[gimpyrobb]

You should be able to find a 12v starter, then all you need is a 12v 1wire alt and a NEW WIRE HARNESS.

24v uses less amperage than 12v, so all the wires on the truck will be too small to carry the rated loads.

Once the new harness is in, just install 12v lights.

Or, you could install a battery equalizer. The 24v goes into the equalizer from the alt. the equalizer then has outputs to each 12v battery. You can tap off the batterys for 12v with an equalizer installed.

Or you can buy a 24v-12v converter. I think Phil(stonepicker) has ones that will maintain a 12v battery.

 

[eagle4g63]

On your switch you found the one "hot" wire then the others are the supply to the lights them selves.....if you put the hot wire back on the switch and test the other legs of the switch, they should be dead with the switch in the off position then they should become "live" when you turn on the switch.

As gimpy said, you would have to change all the main wires if you went to total 12 volt set up.....if you want to have both you can do like gimpy said or you can put that part of the truck back to 24 volt and add a 12 volt secondary system.....that gets a little more involved but lets you run loads and loads of stuff on the 12 side and always have the 24 volt side to start the truck on....you would need a second alternator, easy enough and a 3rd battery, then wire what ever you want into the new system and leave the factory truck wire alone....if you play with electric at all it is actually easier than it seems....most just over think the whole thing.

 

[eagle4g63]

Also, they might not have driven it enough to have messed up a battery yet, or they might have just didn't know why.

 

[6x6XL]

I swapped out a bulb the other day, I didn't really think about it but I ran the numbers on the bulb and it is a GE 1683, which is a 24v bulb.

is it possible the lights are still all 24v and they just wired in the push pull? I was told to "de-mil" these trucks a lot of times they cut the wires off the three arm switch and sometimes in other places. tomorrow ill test the sockets and see if I get the 24v at the lights.

is it possible putting a 12v bulb in the tail light could short or "open" the circuit? I know both the back lights where working until the bulb went out then they went dead.

I work nights so these lights are the only thing keeping me from driving it to work lol.

Thanks for the help so far everyone!