Locating 12-Volt DC Shorts in an RV

Can my 1986 Yellowstone travel trailer have a positive grounded electrical system? When I wire it as a negative ground, I keep blowing 40-amp fuses. Also, would I be better off to use a standard battery charger than the converter? Hank H., (Yuma, AZ)

Hank, I've never heard of any recreation vehicle using a positively grounded DC system. Those even disappeared from the auto industry many years ago. It's apparent, however, that you have a direct short to ground somewhere within the 12-volt DC battery system. Equipped with a digital volt/ohm meter (VOM), it is relatively easy to "ring out" the circuits to find which contains the direct short. Here's how....


The first thing to do is to ensure all 12-volt loads are turned off. Then remove all the fuses from the DC fuse block. Next install a new 40-amp main fuse. If the fuse still blows, the short is between the battery and the fuse box and not likely within an individual DC load circuit. With all the fuses still removed, set the VOM to the ohm's scale and measure for continuity (zero ohms), between the load side of each fuse position of each circuit, to ground. If you measure some resistance, but not continuity, you're probably reading the resistance through that load so make sure it is turned off. You'll be looking for a direct short to ground. 

Some digital meters will have a diode test function which is also good to use. In the diode test setting, the meter will emit a audible beep when there is direct continuity. The circuit that indicates continuity is the problem circuit to focus on.

Next, begin eliminating each device on that circuit one at a time. Obtain an automatic resetting 12-volt circuit breaker and attach two short leads with alligator clips to the two terminals. Use the breaker instead of continuing to blow fuses. Attach the circuit breaker to each side of the fuse holder. This test breaker replaces the individual fuse and will automatically reset after it cools down. This eliminates burning through a pile of fuses during the troubleshooting procedure.

If, for instance, the short is in the lamp circuit on the left side of the RV, turn on each lamp, one at a time until the circuit breaker trips. When the breaker trips, that's the device on that circuit that contains the short. By process of elimination, it will be possible to determine the problem circuit and the problem device on that circuit in most cases.

Once the short is located, in most cases, it's probably easier to run a new wire from point A to point B rather than trying to actually located the exact section of damaged wire. Just cut the wire and tape each end, then run a new conductor.

Standard, automotive battery chargers are not recommended as a 12-volt power supply or as a replacement for a 12-volt converter/charger. I do favor a dedicated smart charger, however. Read my review of the new Xantrex TrueCharge 2 battery charger. The key to correct battery charging is to make sure charger uses algorhythms designed for the type of batteries it will be charging. Shop battery charges simply won't be equipped with that sophistication. And most typical converter/chargers won't as well. The serious RVer should consider upgrading their charging system designed around the premise of "what is best for my battery bank."

Why Do RV Generators Surge?

I recently purchased a toy hauler with a generator with only 27 hours on the meter. At first the governor appeared to be sticking, due to what I believe, bad fuel (varnished). I sprayed the carburetor with a cleaner and it ran fine for a while. The idle still surges with no load applied, and if I put a heavy load on it, it seems to get better. The butterfly plate at the front of the carburetor, when pushed down manually, makes it run smooth. Any ideas? Mike C. (Newbury Park, CA)

Mike, with only 27 hours on the generator I'm surprised you have operational issues so soon. I'm beginning to wonder if the generator ever received a proper set-up at the dealer. For a proper set-up, especially on the older machines, three components must be adjusted in harmony with one another; the carburetor, the governor and the choke (when so equipped).

Though the specific steps are too detailed to list here, you can, at least, check the position of the choke plate; it should be about 1/4 open when the generator is cold.

Prolonged surging is indicative of a governor and/or carburetor out of adjustment. Unfortunately, the carburetor and governor should only be adjusted while monitoring the voltage and frequency and while applying a measured load at the same time. In other words, RV generators cannot be tuned by ear. As I often state in my seminars, every mechanical adjustment on an RV generator carburetor and governor will have a direct electrical result, so I don't condone any tweaking and twisting by RV owners. I'd recommend a generator set-up by a certified technician using a properly sized load bank (see photo). Some individual RV repair facilities may have such a diagnostic load bank, but you're best bet is to take it to a certified shop for your brand of generator when possible.

Also, in severe cases of varnished fuel, it may be necessary to replace the complete carburetor anyway. In the old days, we used to rebuild generator carburetors, but with the newer models, replacement is the better option. (In some cases, the only option.)

Applying the proper set-up steps using a load bank will either eliminate the surging issue or lead you to the right repair track. By the way, if your shop has a load bank, but no knowledge about how to use it, I do have an older training video that is still viable and it just may help. Have your shop contact me.

Replace Anode with Drain Valve?

I was told that it is best to drain your hot water tank after each excursion, therefore I replaced the anode with a petcock. I now drain the water out but am curious as to the soundness of this plumbing exchange. Any advice would be appreciated. Gary G., (Monessen, PA)

As far as draining after each trip, Gary, a lot depends on how often your excursions actually take place. Personally, I would only drain the water heater in preparation for winter storage, a lengthy period of non-use, when servicing the water heater or when chlorinating the fresh water system. Or perhaps when you encounter some foul water during a trip. But, remember the anode in the water heater is a necessity when the heater is in use, but only for Suburban and the older, American Appliance brands of water heaters. Water passing through the tank creates an electrolysis that will literally attack the tank from the inside. The anode is the sacrificial component that prevents the tank itself from becoming damaged. If you still want to drain the tank, simply remove the anode/drain plug. 

On the older American Appliance heaters, the anode had a separate connection on the rear of the heater, plus they were originally equipped with a drain cock anyway. I realize it is probably easier to drain with the valve, but it's more important to have that anode in the tank. In the long term, it will be worth the extra time it may take to drain the heater between trips. 

As a side note, I’ve seen some mis-information posted on  online blogs recently and wish to clarify when to replace the anode. Suburban recommends replacing the anode annually or when the rod has about 25% of its original size left. Heavy travelers may need to replace the anode more than once per year, but typically, once per camping season usually suffices. If you are a full-timer or travel often, check the anode at six-month intervals and replace it when it’s 75% deteriorated.

RV Oven Operation

The Suburban oven in our older RV is acting up. The pilot lights normally and when turning the control to a cooking temperature the flame goes large and the signal to light the burner seems to be received and the main burner comes on. So far so good, it appears to be working. The problem is the oven only heats to a certain point (not even 300-degrees according to a thermometer) and the main burner goes out, acting as if it reached the temperature the control was set at. It seemed to me a problem with the safety valve/control unit or the sensor, so I started looking around for a replacement part. A few dealers tell me there is no replacement part made and I have to buy a whole new range/oven control unit. Visiting Suburban's website does not shed much light except that if there was an "A" after the model number it would be a mercury free unit. I wonder if it could be retrofitted? Gord S., Edmonton, AB

At first read, Gord, the safety valve appears to be functioning normally, assuming the delivery line pressure is set correctly. Any pro RV service facility can quickly and easily set the propane pressure for you. With correct pressure, here's what happens when you set the thermostat to any cooking temperature: When the thermostat is set to a temperature (assuming the oven pilot flame is lit), the pilot becomes slightly larger and begins to heat the thermal bulb (or a thermocouple in a non-mercury valve) attached to the safety valve. Yours appears to be doing this now. This thermal bulb, when heated by the pilot flame, expands a bellows in the safety valve and allows the propane to flow through the valve and on to the main burner where it is ignited by the extended pilot flame. This results in a time delay from when the oven thermostat is first set to a desired temperature until the main burner actually ignites. Now all that said, it is a possibility you have a faulty thermostat (main oven control valve). But first be sure the temperature sensor inside the oven is clean and free from cooking oils, oven cleaner and grease, etc., before condemning the thermostat control.

Your problem may simply be a fouled temperature sensing probe in the oven. A coated probe can send incorrect info to the oven thermostat control. If faulty, however, the thermostat and temperature sensor must indeed be replaced as a single unit since an integral capillary tube connects them. Your first task should be to clean the temperature sensor in the upper reaches of the oven. But it's also possible the oven safety valve may be the culprit. The flame sense probe (thermal probe) at the oven pilot is an integral component of the safety valve and must be replaced as a single unit like the thermostat and its temperature sense probe. I'm sure this sounds a little confusing, but a certified RV service tech should be able to quickly diagnose the problem with a few measurements and a couple of operational tests. So, clean the temperature sense probe and have the LP pressure verified keeping in mind further diagnosis may still be required. I don't believe it’s plausible, or even possible to replace a mercury safety valve with a non-mercury valve without drastically modifying the range. And it certainly is out of the realm of the do-it-yourselfer. 

RV Toilet "Scored" And Not In A Winning Way!

You have helped me several times in the past and now I have a minor problem. The toilet brush we have been using has really "scored" and scratched our RV toilet badly. I have managed to get rid of the gouges with rubbing compound and then car wax. My question is: What can we use to clean the toilet without leaving the scratches? (We think the brush we were using is designed for ceramic toilets). Many thanks! John E., (via RV Doc Newsletter)

John, I’m not a big fan of plastic RV toilets for the very reason you mention. They are simply not compatible with most abrasive cleansers and bathroom brushes. I think you’ve done the best thing you can to rectify the issue though. If the car wax contained carnuba, that will help. Future cleansings should be performed with a strictly, non-abrasive cleaner and use a very soft brush. Personally I don’t have a favorite, so any non-abrasive cleaner is a potential. It may take some experimenting to find the one best suited for you. 

And thanks for signing up for the free monthly RV Doctor Newsletter John! Lots of good info found in there each month. Information not available elsewhere! 

Don't be the last on your block to subscribe! (See the 2nd box down on the right-hand side of the RV Doctor Website to sign up)