In an equal equity partnership, partners' capital accounts should reflect the fair market value (FMV) of assets contributed, rather than self-declared values or historical cost. The fair market value ensures equitable ownership distribution and accurate financial reporting.

Let’s analyze each option:

Option A: The capital accounts of the partners should be increased by the original cost of the contributed equipment.

Incorrect. The original cost (historical cost) of an asset is not relevant in partnership accounting. Instead, fair market value (FMV) is used to properly recognize each partner's contribution.

Option B: The capital accounts should be increased using a weighted average based on the current percentage of ownership.

Incorrect. While ownership percentages influence profit and loss distribution, initial capital contributions should be recorded at FMV, not a weighted average.

Option C: No action is needed, as the capital account of each partner was increased by the correct amount.

Incorrect. Since the partners contributed different self-declared values, the capital accounts may not be correctly recorded unless verified against FMV. The partnership agreement typically requires capital contributions to be valued based on FMV, not self-declared estimates.

Option D: The capital accounts of the partners should be increased by the fair market value of their contribution.

Correct. Fair market value (FMV) ensures that capital contributions are recorded accurately. Using self-declared values without verification can lead to misstatements in capital accounts and potential disputes.

IIA Reference: Internal auditors reviewing partnership accounting should ensure that capital accounts reflect fair market value to maintain financial accuracy. (IIA Practice Guide: Auditing Fair Value Estimates)

Thus, the verified answer is D. The capital accounts of the partners should be increased by the fair market value of their contribution.