hi had the same problem with negative connection i solved the problem with the connection i found in the chandelry a single round post around the base were about six connections for other connectors so two cables from battery to shunt nasa cable from shunt to post, negative wire from service battery to engine battery goes to top of post completeing the loop
the shunt will only read power draw from service battery bank
it works just complicated post has large terminal on top to take the battery cable did use nasa cable .
hope this helps
john d