Rallye cluster question
You photo as mentioned--too small but it appears to be a noise suppression cap/ condenser. You MAY not need it with an RTE/ other electronic replacement
To test, you'll need some resistors or a variable rheostat that you can set to specific resistances
This is a photo someone "shopped" showing an aftermarket gauge tester and the resistances needed, one for "empty" one for 1/2 scale, and one for "full." All three gauges should show same readings but test them one at a time. Put the resistors from each gauge sender terminal "in turn" to ground