This information has been discussed many times here on the forum and in an effort to preserve and reference it (in the future) I wanted to provide additional information and clarification on Zamp Solar's panel connections and when using a battery tender. This is basically an extract of the information
I previously had posted up over on the Little Guy forum back in 2016.
Zamp wires their solar panels in an effort to make them safe to use and in an effort to avoid accidents since the panels do convert sunlight into energy and it is possible for a user to put themselves in series with a solar panel and receive an electrical shock should they become part of the circuit when hooking up and using a solar panel. This is true whether it is a Zamp solar panel or any solar panel you may be using since they are able to generate energy when in sunlight or for that matter, any ambient light they come into contact with.
The photo below shows the stock Zamp Solar Port wiring harness that comes on all of the trailer units and is located either on the battery box, sides of some trailers and on the tub of the T@B and T@G trailer units. This piece wires directly to the trailer battery and as you can see in the photo the positive (+) side (red wire) of this harness is the bare contact terminal, negative (-) side (black wire) is the female part of the solar port.
The photo below shows the style of connector that would come off the end of the newer Zamp solar panels. In this photo the positive (+) connector (red wire) is the female style end. Zamp wires their solar panels in this manner to protect users from accidental shock accidents. The bare end of the connector shown is the negative (-) terminal (black wire) and this is where some of the confusion comes into play when people discuss the "Battery Tender" brand of trickle charger, as their terminals are wired directly opposite of the Zamp wiring scheme shown below. Note
: The gist of Zamp's safety intent here is that should you deploy "any" solar panel and have wires connected to it in full sunlight it is producing electrical power. If the above wiring is connected to a Zamp solar panel the risk of being injured is reduced here because the "positive end of the cable" coming from the panel has an insulated plastic coating over the energized (+) cable end. By wiring their panels in this manner it greatly reduces the potential of accidental contact should you have the cable ends in your hand. Battery Tender brand trickle charger wiring explained
In the photo below you can see that the Battery Tender units are wired opposite the Zamp solar connections and unless these terminals are wired in reverse you will not be able to charge up your trailer battery if you plug a Battery Tender into the Zamp Solar Port on your trailer. In other words you would need to do the following with the battery tender trickle charger unit:
1. Cut the charge wire coming off the back of the Battery Tender unit, reverse the wires and splice them back together.
2. Use the clip on style connectors shown just to the right of the tender unit and attach them to your trailer battery when charging the trailer battery.
Unless you follow the above steps the Battery Tender unit will not charge your trailer battery if the tender is plugged into a Zamp Solar Port and this issue has confused many trailer owners as a result of the way Zamp wires their solar panel wiring harnesses.
The bottom line here is that Zamp Solar does not wire their solar ports for use with the Battery Tender brand trickle charge units, but only wires them for Zamp Solar equipment and apparatus. Therein lies the difference and hopefully the above information will help people understand the reasoning behind Zamp Solar's wiring set-ups and provide them with enough knowledge to use a Battery Tender in charging a trailer battery when it has a Zamp Solar connector wired into the trailer and hooked to the battery.