I installed this
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Isolator Relays / Intellitec Isolator Relay B.I.R.D. Diesel 00-00839-000
Intellitec Isolator Relay B.I.R.D. Diesel 00-00839-000
charges both sets of batteries in both directions, they say to use your jump start relay, but I added its own relay, so if it fails the jump start relay will still work