General one-leg and multistep methods for mixed systems of implicit differential equations and algebraic constraints are defined. Such systems are encountered frequently in circuit analysis. Three different implementations of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A (\alpha)</tex> -contractive two-step Adams method are shown to be second-order accurate by an analysis of the local truncation errors. These methods are tested numerically against the familiar two-step second-order backward differentiation method.