30-amp Reverse Polarity Fuses Blowing on Camper Converter

Updated 07/31/2026 | Published 07/23/2026

Question:

I have a 2000 Lance truck camper that I recently noticed that when plugged into shore power it is not keeping battery charged,purchased new battery and noticed when connecting small black wire to positive it keeps blowing the 30 amp reverse polarity fuses.All connections are connected as should be as shown in manual and before old battery was removed could this be the converter gone bad? All other 110 works a/c,microwave electric plugs, just not charging battery and blowing out the 30 amps fuses all wires look good nothing looks burnt or smells burnt. I recently purchased the replacement converter for the 7300 4345 but I wanted to ask before installing it

asked by: Debbie R

Expert Reply:

Hey Debbie,

Based on what you described, it does sound like an issue with the converter, especially since the appliances are working but the battery isn't charging. One thing to note, though, is that the 30-amp fuse is meant to blow in cases of reverse polarity. It's possible that the wiring on the 12V charging circuit is wired in reverse and it's blowing the fuse to protect the converter. Since you've confirmed the battery connections match the wiring diagram and the issue is also happening with a brand-new battery, the next step being replacing the converter would be correct. The new converter (I recommend the Progressive Dynamics Replacement Section for AC/DC Power Distribution Panel # PD4645V in these situations) should resolve the issue and if it doesn't, there's likely a short somewhere between the converter and the battery and you would need to check the run of wires between the converter and the battery for any damaged wiring or chafing.

Can you tell me which replacement converter you purchased, and does the fuse blow instantly when you connect that small black wire even with the RV unplugged from shore power? Are you staying lead-acid or considering lithium for your Lance?

expert reply by: Jerry B

Markt

7/30/2026

Debbie, Where is this "small black wire"? At the battery? RV's often use the 120v AC "house" wiring conventions where Black is "hot" and white is "neutral" (effectively ground). This can be very confusing as the 12v DC wiring convention says that Black is "ground". So that "small black wire" you are connecting might actually need to go to the positive side of the battery OR negative side of battery. It sounds like in your case it might need to go to the negative side of battery? Usually an RV manufacturer follows the normal "black is ground" right at the battery even if they use "black is positive" at the 12v lights or appliances. If you have the Lance owners manual, it might have wiring diagrams that will help. (Red is generally "hot" in both AC and DC wiring color conventions)

Jerry B.

7/30/2026

@Markt That's spot on. I wish there was a universal standard with RVs, but unfortunately everyone does their own thing. Thanks for your help there!

Andy M.

7/30/2026

Jerry is absolutely correct about the power converter being bad. However, it is wise to test polarity via a meter. Place the red lead from your DC meter to the red wires and the black lead from the meter to the black on your unit. If it shows negative, then you know your camper is wired with a hot black wire. That can be part of the problem. You can also ohm out the black wire to the camper or truck after disconnected to see if the black wire is ground or the red wire is ground. Also, another good check is to disconnect your outlet from your converter to your battery and make sure the voltage is reading between 12.8 to 14 volts DC. The new power converter is a 45 amp converter which is better than the older converters and your loads may be causing the old power converter to overload for some reason. If you keep blowing fuses after the new converter is installed, then you have some other issues causing an overload from your camper. Probably some type of short if it keeps blowing 30-amp fuses. Definitely check your converter outputs prior to connecting the battery backup. I do know that Lance uses some different wiring configurations compared to other manufactures that is why it is so critical to check everything with your meter prior to hooking everything back up.

Jerry B.

7/31/2026

@AndyM Thanks for your assistance there! You sound like you've gone through this a time or two. Haha would you consider yourself a professional or just an experienced learner?

Andy M.

7/31/2026

@JerryB. Technician and electrician by trade. 40+ years in power plant business.