Sounds like you have the OEM R/R.... Recommend that your replace it now or eventually the thing will die anyway. Check here -- www.roadstercycle.com and order the FH020AA.
Dont go cheap and get one from Ebay.
Skip wiring into the existing harness connector and go direct like I described. Tape up that connector and forget about it.
If you dont want to spend $ now, I would butt connect/solder the 2 red wires together with a longer red lead and as I said, you need a HD fuse box and hook to the pos battery side. (10 or 12 gauge lead) Then again, butt connect the 2 green wires together with a black lead, and connect to ground or the battery ground. Again, 10 or 12 gauge lead. - Then do the voltage test with the voltmeter at the battery. (Dont just use one of the 2 red wires and just one of the 2 green wires.)
A good vendor for electrical stuff is ---
http://www.cycleterminal.com/index.html
Some butt connector styles - -- (get marine heat schrink tubing from Harbor Freight_ -- HF has a very good marine HS kit)
https://www.amazon.com/Lucksender-Uninsulated-Terminals-Connector-4-0-6-0mm/dp/B010FMHUSC/ref=pd_day0_328_5?_encoding=UTF8&psc=1&refRID=P7RYAW6E8WKFD0D5QE8K
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https://www.amazon.com/Baomain-Uninsulated-Terminals-4-0-6-0mm2-1-5-2-5mm2/dp/B0186S0CW8/ref=pd_day0_328_3?_encoding=UTF8&psc=1&refRID=P7RYAW6E8WKFD0D5QE8K
If your head stratching on what fuse holder to get.. get this one. - Metri-Pack 630 ATC fuse holder. 12 AWG (guage) - simple its already assembled. One side to the 2 R/R wires the other to the battery - you will need to get a HD ring terminal.
http://www.cycleterminal.com/fuse-boxes.html
http://www.cycleterminal.com/ring-terminals.html
You need to do a clean job and not half ass the assembly of this too, otherwise your still asking for problems....
A good thing to do is add a digital voltmeter up front so you can watch how things are going. - Mine saved my behind this season...
GL