Heater Ignitor Works On 110V But Not Battery

A piece of red tape on the positive battery wire is not a bad idea. Also a piece of red tape next to the positive post helps at times because of the difficulty of seeing black on black battery marks in low light.

Many moons ago when I bought my first used RV, I made the newbie mistake of thinking the black was negative also. Each and every unit I've had since one of the first things I do is , on the inside of the battery door I write: Camper is wired like a house not like a car. Just in case somebody who might be helping me doesn't make the same mistake.

Yeah I think everything may be okay. Does anyone know what size fuse should be in the fridge? Heater works great now. Luckily this is a basic camper and the only thing electrical in it besides lights is the fridge. I still can't believe this guy hooked the battery up backwards. I was planning on buying the camper and he called to tell me the heater was not working so he replaced the battery however it still didn't work although the fan was kicking on. I didn't think much of it and bought it last weekend. Lesson learned. Hopefully it will not be an expensive mistake.

Sounds like your on the right track now. Might be a good thing that your fridge fuse is missing, time will tell.

Here's an important learning lesson. When you buy a used camper that someone else has worked on make sure the battery is connected correctly. The problem was the fan was running backwards and the cables on the battery were switched. After testing the cables with a voltmeter I was able to confirm they were wrong (thanks to the advice found here). I can't believe it didn't fry a fuse but they are all still intact. Trying to make sure the fridge works but I have found there is a fuse missing for it (found that while tracing his problem).

OMG, yes, that is backwards and that would explain the smoke when you grounded it out.
RVs use house-wiring standards rather than car - cars, black is ground, RV's and houses - black is hot. But wait, there's more... There are exceptions - a lot of times wires for solar come down as black and red, likewise, sometimes people (like me) add stereo equipment to their TCs and those wires might also be car-type black/red. General rule - black/red together - black is ground, black/white paired together, white is ground. **disclaimer - Take your TC to an rv tech before taking this as the gospel**.

I would be very surprised if nothing is actually fried.
Things to check to see if they're fried - fridge, electric jack controller, stereo, any 12v tv/dvd player if you have one.

Yes it would and your fan motor would run backwards.
Disconnect your battery terminals and plug in your camper umbilical cord to 110v. Put a voltmeter on your battery leads and see if your polarity matches up.

I'm out at the camper right now working on this problem. The fan is noticeably faster running on 120 volt shore power. The battery is fully charged and the voltage hardly drops when the fan kicks on. I ran an external ground from the battery to a jack with jumper cables but that didn't help. I also ran it directly to the heat frame and it started to smoke. Next question, and excuse me if this is dumb. Could the battery be hooked up backwards? I bought the unit with this problem and here is what I'm finding. There is a black cable going to the (-) on the battery and a white cable going to (+). Tracing the cables as best I can (they disappear for a moment behind a cabinet and I can't see them) the black cable from the battery runs to the inverter. The white cable disappears and I can't trace the entire thing. All I know is at the jack mounting bracket on the outside of the camper I have a white cable (very similar to the one hooked to positive on battery) and a green cable that comes off the inverter. Could this white cable be the one on the (+) of the battery? If it was hooked up backwards would anything actually work?

I agree that it could be a wiring problem causing low voltage to the heater (specifically to the blower motor).
However it could also be a problem with the "sail switch". You can see the sail switch at 2:05 in this YouTube video (note that depending on your make/model the switch may be slightly different or in another location).
Cheers,
-Mark

I knew I came to the right place. Thank you for the suggestions. I'll try all of them starting with the ground first since it's the easiest. I should have time tonight to take a look. I'll report back on what I find. Thank you again.