OT electrical help with camper trailer

[fishfrnzy]

I hope someone here can help and electrically challenged person. I bought a 10 year old pup up camp trailer that has the following accessories converter, heater, fridge, lights, CO alarm & water pump. Of course it came without a battery. It is supposed to charge from my vehicle while towing. It has three wires to hook to the battery. One white which bolted to the chassis so I know that is ground. One red that (with 30 amp fuse) that plugs into a black wire that disappears into the front of the trailer that I know goes to positive terminal.

Then there is this problem green wire (with 15 amp fuse) that plugs into a black wire and goes back toward the converter and also disappears into the trailer. I believe this should go to the positive terminal but what trouble me is it seems to have continuity when checked with a meter at 2000 ohms and seems to have continuity when checked against the ground wire. The meter is a cheap HF digital and I get readings from the low 200 down to 001 or 000. I occasionally will get minus readings also. I admit to being completely ignorant in how to use a meter but occasionally can get a useful answer from one of the things.

I tried hooking up red to positive and green and white to negative going with the theory that if I have continuity then they must both be ground wires but then the lights, pump etc don’t work. I would really rather not fry anything so thought best to ask some of the old pros here. The green wire will spark if I scratch it on the positive terminal, for what it’s worth.

thanks in advance

[J Tiers]

So, what's the "converter"?

Something that makes 110V? Something that makes a lower voltage than 12V?

Do you know it is good?

if it's something electronic,and it makes sparks against +12V, it may have capacitors, it may present a legitimate load to the battery, or it may be bad and drawing current when it should not. Presumably it isn't very powerful (15A fuse @ 12V) and it must get its ground from the frame of the trailer.

[fishfrnzy]

The trailer accessories run off 12 volt DC but has a shore power 110 male plug so I believe it just converts 110V AC to 12V DC. According to schematic I found in a manual it seems a black wire with 20 amp fuse is supposed to go to converter. Supposedly, when the tow vehicle is charging thee power goes to the converter then back to battery?

"do you know if its good?" no, I don't, except when I plug into 110 all accessories work fine.

is there any reason for a ground or negative cable to have fuse on it?

[Paul Alciatore]

As an educated guess, I would think the green wire is also a positive feed, possibly to that "converter" (do you mean an INVERTER that produces 115 VAC for standard household appliances?). The sparks you see when you touch it to the positive terminal probably mean the inverter is operating and drawing some current. If it was grounded, you probably would have a much bigger arc and the green wire would get very hot. You say it has a 15 Amp fuse and did not say that it blew. So, the current is probably less than that.

I would use a meter, probably a better one, that can measure DC current and check the amount of current it is being drawn when it is connected to the positive terminal (for a real short time). If you can disconnect that inverter at the inverter, then do so and see if the green wire still draws that current. It it goes to zero current with the inverter disconnected, then it should be safe to believe it is a feed to it and connect it to the positive terminal.

If that's not the case, post more information and possibly a photo or two.

[CarlByrns]

As an educated guess, I would think the green wire is also a positive feed, possibly to that "converter" (do you mean an INVERTER that produces 115 VAC for standard household appliances?).

He means 'converter' - it's a power supply that knocks down 120VAC to 12VDC. All important accessories on the camper (lights, furnace, water pump) are 12 volt.
Small campers rarely have inverters because of the expense and the amount of space the batteries take up.

From his testing, the converter is working fine.

[portlandRon]

Any wire that has a fuse normally would go to positive.
I say "normally" because there is no tilling what past owners may have done to the wiring.
But being fused it should not damage anything by connecting it to positive and seeing if the equipment works.
If it does blow the fuse quit possibly it's not wired wrong but a problem with one of the units.

[bborr01]

Green is generally a ground wire. That is what I would suspect.

Brian

[jdunmyer]

As CarlByrns says, when discussing campers, the "converter" converts 120 VAC to 12 VDC.

Dunno about the OP's converter, but I've run into 2 flavors: one is not much more than a big 12 volt battery charger, it has 2 output wires, the negative (usually white) and the positive, usually black. The other flavor has a negative and 2 positives: one is regulated and goes to the battery to charge it, the other is unregulated and feeds everything in the camper, lights, fans, water pump. If there's a radio, that's fed from the regulated output, as the unregulated is often unfiltered.

When changing from the 2nd type of converter to the 1st, you simply tie both positive leads (going to the camper) together.

[1-800miner]

Does it have electric trailer brakes? Would one of the hot wires be for that?

I am confused. The battery you refer to is it the trailer or tow vehicle battery?

[CCWKen]

No sense guessing at something as important as wiring. I'd be looking for an owner's manual. It should have a wiring diagram. If no diagram, I don't see a choice but to trace the wires. Even if it means removing a panel or two. There may be a battery isolator in there somewhere too. Or it may be nothing but a large diode. The isolator allows the vehicle's alternator to charge the vehicle battery and the camper battery but prevents the camper battery from back-feeding to the vehicle or drawing from the vehicle battery.

I had dual batteries on my boat with an isolator. One battery was strictly for hull venting and starting the boat and the other was for all other accessories. This meant I could run the lights, radios, bilge pump and others until the battery was about dead but I could still start the engine.

[fishfrnzy]

Does it have electric trailer brakes? Would one of the hot wires be for that?

I am confused. The battery you refer to is it the trailer or tow vehicle battery?

No trailer brakes on this one. Deep cycle battery is on the trailer but when being towed is charged by towing vehicle, through the converter I believe. I will pull off the converter over the weekend and see if that is same wire. I'll try some of the suggested above.

Thank you all for the replies.

[darryl]

In some trailers I've seen wiring that corresponds to house wiring as far as color- that means the white would be the ground or negative and the black positive.

When you look at the 'converter', it should say which is negative and which is positive. I'm pretty sure you're right about it being a 110 to 12v converter. If there's a model number on it it's likely it can be looked up on the net and something known about it then.

[CarlByrns]

Deep cycle battery is on the trailer but when being towed is charged by towing vehicle, through the converter I believe. I will pull off the converter over the weekend and see if that is same wire. I'll try some of the suggested above.

Thank you all for the replies.

Charging the trailer battery from the tow vehicle would be unusual, but not outside the realm of possibility. The charging circuit should have a diode isolator so that the tow vehicle can't drain the trailer battery.

[AD5MB]

So, what's the "converter"?

Something that makes 110V? Something that makes a lower voltage than 12V?

more likely something that makes much more than 12 VDC. what us electronics folk call a brute force DC power supply fed by shore power. a vast transformer and a full wave rectifier that generates poor quality unregulated DC at voltage levels that overheat lights, melts lenses and cooks electronic power supplies. useful for the 12 V refrigerator element, the furnace fan, the water pump and not much else

the quality of the DC can be vastly improved with a stiffening capacitor. boom car owners pay ridiculous prices for them from car stereo shops. electronic technicians get them from surplus stores for a buck.

I would convert to LED lights and run lights and electronics off a switching power supply, which can be bought for chump change from eBay.

is there any reason for a ground or negative cable to have fuse on it?

ham radio types have learned the hard way to fuse the ground lead of high power transceivers, because a high power unit that loses its DC ground will search for a ground through other devices, generating massive heat in the device that ends up being the ground path.

Does it have electric trailer brakes? Would one of the hot wires be for that?

trailer brake wires are blue. resistance: 2 ohms. big spark, big clunk. trailer brakes lock up on gravel at about 3 volts. testing with full battery power is not prudent.

Charging the trailer battery from the tow vehicle would be unusual, but not outside the realm of possibility

this is done with trailer brakes and vast trailers with DC refrigerators. trailer brake batteries are small for a reason. you only want them to work for thirty seconds while the trailer dives for the shoulder of the road after the hitch breaks. if you tie it into the vast Group 65 batteries I use for the winch on my car hauler, it would sit there smoking until the battery cables melted.

green wire is traditionally right turn and stop on trailers

https://www.etrailer.com/faq-wiring.aspx

[J Tiers]

Obviously not that "vast", likely short of 175W due to the 15A fuse. Presumably for charging whatever on-board batteries are available for the trailer (other than for brakes etc). And, equally presumably pretty lame as far as a charger.

Charging batteries would be why you consider it a tool for destroying equipment. Batteries charge at north of 14V, cheap 12V equipment does not like 15% higher voltage.

I have noticed that trailer people are the worst electrical/electronic folks on earth..... Cheapest sub-par wiring and fixtures imaginable in expensive travel trailers and RVs. Makes me understand why I have seen several burning alongside the road. A cheap motel is built a lot better.