I have a Garmin Tandem … I can connect another rear view but haven’t … I connected with this from Amazon and works flawlessly. No splicing!
https://www.amazon.com/dp/B088P4VFQ7/ref=cm_sw_em_r_mt_dp_W80DP7R4SM3GHVSE1TZ3?_encoding=UTF8&psc=1
Apparently my ears suck ... I have an 8 speaker system in my Lariat ... but I see there are 18 and 21 ... but mine is awesome ... like, where are all those other speakers?