Arcturus;
In series with Ign Power supply to Instrument, and external to Inst is fine (IOW, Inst does
not need to be removed to add DR...you could simply add it externally, between supply [there are multiple wires as terminal is used as a common tiepoint] and Inst power terminal).
Like so:
See also:
https://www.sw-em.com/Fuel%20Gauge%2...nstrument_data
Cheers