Continuing ignition saga

Naive question here. On my '76 TR6 there's a blue gizmo with a wire attached
to the coil and mounted on the coil bolt. Is this the ballast resistor? If
it fails will it cause the stalling and intermittent spark symptoms, can it
be tested, and is it available anywhere? It's not in the Moss diagram or
anywhere else that I can find. It's the only ignition part I havn't
replaced! Thanks.
Craig

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