Tracing A Short On 24Volt System

madmike · Post by **madmike** » Mon Jun 22, 2009 10:30 pm

I have noticed that each time I connect the ground cable to my M38A1 I get a small spark. I presume this is not normal and, if I leave the cables attached, I lose charge. I disconnected the main light connector behind the gauges thinking it was likely a light shorting out but still have the problem. If I next disconnect the gauges, I won't be getting current thru the lines from the amp meter gauge. Or will I ? Any suggestions on tracing this out? If I disconnect the ignition switch, is current still going thru the gauge?

kenperkins · Post by **kenperkins** » Tue Jun 23, 2009 4:59 pm

last time I had this problem it was the foot starter switch. take it off, open it up. and see if it is burnt. I got some computer board material and made new insulators between the contacts.

Post by **wesk** » Tue Jun 23, 2009 9:18 pm

A small spark when connecting the cable with the old style mechanical voltage regulator is common due to the radio noise filter (capacitor) charging. When removing the cable there should not be any spark. The way to check it out is to disconnect the battery ground cable ( the battery ground closest to the frame ground). Connect a 24 volt test lamp between the terminal you just removed and the empty battery post. The light charging of the capacitor will not cause the test lamp to stay illuminated.

If the lamp glows you have a current draw somewhere. If all switches are off then disconnect one circuit at a time until the lamp goes out. When it goes out you've found the short. Keep in mind that you should temporarily disconnect the test lamp while you are wrenching on the ataachment you wish to disconnect or reconnect to prevent an accidental short melting something down.

Using the wiring diagram below start by:

1-Disconnect 82 and 4 from the starter switch, hook them together so the regulator and the dash stay powered up.
Light on switch is not the problem. Lite off switch was the problem.
re-connect proper wires to proper locations.

2-If light stayed on. Then disconnect 10 at the double connector behind the dash.
Lite goes out problem is in one of the circuits running off #10. Lite stays on re-connect 10 to the double connector.

3-Disconnect wire # 9 at amp meter. Lite goes out problem is in amp meter, wire #8 or regulator shunt. Lite stays on re-connect #9 and disconnect #8 at amp meter. Lite goes out problem is in amp meter, wire #8 or regulator shunt. If lite stays on disconnect both #8 & #9 and connect them to each other. Lite goes out the amp meter is the problem. Lite stays on the voltage regulator shunt is the problem.

This is all there is to it. Go slowly , write down what you do so you always know where you were, where you are and where you will be next. Take your time. If the wiring is quite old then also suspect each Douglas connector and inspect them closely for rotten insulators and bare wire touching the metal parts of the connector.

DFoley · Post by **DFoley** » Wed Jun 24, 2009 10:30 am

I am having a similar problem on my M38. This past weekend I removed both 2HN batteries and placed them on a slow trickle charger over night. The next morning the chargers indicated the batteries were both fully charged. Reinstalled the batteries, and she started up just fine...today went out to start her up and nothing. Got my volt meter out and the battery under the hood read ~12 volts and the battery in the cowl read ~9 volts, together at the axillary power receptacle I get a reading of ~22 volts (I only have an analog meter, so the exact voltage is difficult to determine). My question is how do I tell if the batteries are the problem (unable to hold a charge) or is there a short somewhere causing the batteries to be drawn down. My batteries are fairly new (~13 months old)

Thanks,

Post by **wesk** » Wed Jun 24, 2009 10:48 am

When the batteries self drop to two different voltages you have a problem with the lower reading battery. Start by buying a $15 digital volt meter. An investment you won't regret.

Remove both batteries from the jeep, clean their cases with a water/baking soda mix, check their fluid levels and service if needed and charge each seperately overnight at about 2 amps.

In the morning disconnect the charger, wait one hour and take a reading of the battery's voltage. Write it down. Now read the voltage in each cell by touching your plus probe to the positive post and touching your minus probe to the fluid in the cell closest to the positive post. Record the voltage reading (don't let the probe touch the plates in the fluid).

Now move your minus probe to the next cell and move your plus probe to the cell you just pulled the minus probe from. record your voltage reading. Continue this all the way across the battery to the negative post.

One reading will be about zero but the other six readings should be 1.8 to 2.2 volts. They all should also be within .2 volts of each other.

I'll bet the battery that only had 9 volts in it has one or two bad cells and these will read quite low.

You can also invest in a battery hydrometer and use it to learn the state of charge of each cell by checking their specific gravity.

Finally checking the batteries under a load is required to complete the checkout of each of them. The easiest way is with a carbon pile type load tester but you may not have one of those so the second easiest way is to take the battery to a battery shop and have them load test it. There is also a complicated way to connect a series of headlamps to equate to the battery's amp hour rating and record the voltage drop over a specific time period.

Always rinse your probes or anything you immerse in the battery's electrolite with a solution of water and baking soda when you are done.

As for the vehicle causing your loss of voltage just follow what I posted above.

Cacti_Ken · Post by **Cacti_Ken** » Wed Jun 24, 2009 9:40 pm

That is very interesting Wes, I didn't know that the voltage could be measured by sticking probes in the water to measure the cell voltage.

TomM · Post by **TomM** » Thu Jun 25, 2009 7:21 am

Mike,
Check out this thread about half way down is a reprint by Ryan regarding spark on battery connection:
http://www.willysmjeeps.com/v2/modules. ... pic&t=2777

I have a spark every time I connect the batteries. This was confirmed by using a current meter in line with the battery leads. There is only an initial surge for the caps then current flow goes to zero indicating no shorts.

Tom

Post by **wesk** » Thu Jun 25, 2009 7:43 am

Tom is correct. However that is a very light momentary spark on connection when the radio noise filter absords a sudden charge. A fat very noticable spark going both on and off with the cable is the indicator you are looking for that ID's the existance of a real problem. The connecting in series with the ground a test lamp is how you confirm that you do indeed have a current leak somewhere.

TomM · Post by **TomM** » Thu Jun 25, 2009 8:01 am

Right
So once you have confirmed that you have or do not have a short...
assuming you have a short you will see - big spark on connection and disconnection, current continuing to flow even with everythng disconnected.
Now go to troubleshooting.
If you had easy access to the electrical system you could probe but since the waterproof connections make it hard to get volt readings the easiest troubleshooting process is isolating.
You already said you disconnected the lighting circuit with no change. keep it disconnected. It appears you may rule that out as a start.
Then disconnect the second (thin) wire on the starter that leads to the breakers.
If you still see the spark, you will have isolated the short to the starter or battery cables.
so disconnect the fat wire on the starter. Still a spark? problem is somewhere on the battery cables.
No spark? start looking at your starter as a short. As mentioned it is not uncommon for carbon to build up in the big switch and create a short.

Through process of elimination you can isolate the errant circuit pretty easily assuming bubba didn't fool with your wiring.

Tom

Post by **wesk** » Thu Jun 25, 2009 11:30 am

Look out Tom! The A1 doesn't have the circuit breakers. Also disconnecting the fat wire at the starter is misleading since you not only seperate the starter from the batteries you also remove all the other circuits. As I showed above disconnect the fat cable #82 from the starter and connect it directly together with #4 the skinny one that was on the starter also. Now you have eliminated the starter and retained all the other circuits and the regulator and if the light went out it for sure is the starter. If it did not then he needs to just follow my list above.

TomM · Post by **TomM** » Thu Jun 25, 2009 11:35 am

OOPS
Agreed - I was thinking M38 and not A1.

Thanks for catching that.

Tom

Tracing A Short On 24Volt System

Tracing A Short On 24Volt System

spark

M38a1