There is a positive and negative on the 12 volt side of the reducer that would go to the fuse block. Should he be using some sort of inline fuse from the pack going to the reducer.
1 In 6 Out Independent Positive And Negative Of The Fuse Box With Led Indicator
Inline fuse positive or negative. It depends on the circumstances. Is it best practice to remove one of the battery cables in the pack when working on a series cart for safety. In an isolated circuit the fuse could be on either the positive or negative lead it makes no difference since the same current is flowing through both. Connect the fuse to the negative terminal of the battery since its where the actual flow of electrons originate which is opposite to the conventional flow of current from the positive terminal. Fuse responds to excessive current not voltage or polarity. Positive or negative side doesnt matter.
In a car or truck or other vehicle where the metal chassis is connected to one of the ends of the supply typically the negative it would be mandatory in that case to fuse the positive leads and in most cases desirable to switch the wire that was not connected to the chassis as well. Fuse goes in series with the load to protect the power supply if the load shorts out. Connect the fuse to the positive terminal. When working on battery stuff like this. On the back of the lighter there are 2 connections one is labled positive the other is labeled negative. Also this is a series cart with no run tow switch.
In all vehicles where the chassis is at ground potential almost all cars then the fuse should always be on the positive lead and as close to battery as possible. Should he also run a negative from the battery pack negative directly to the fuse block negative as well. Wire the positive connector to the positive terminal on your main. Connect two fuses one at the positive and one at the negative battery terminals.