The trust scale is a 17 item questionnaire.
Items are scored on a -3-3 scale, with the total scale score calculated as a sum of the 3 sub-scale totals.
These are predictability, dependability and faith.
Rempel, J.K., Holmes, J.G. & Zanna, M.P. (1985). Trust in close relationships. Journal of Personality and Social Psychology, 49, 95-112.