What can cause a 90 ford probe to run only in reverse?

If a 1990 Ford Probe only runs in reverse, it may indicate a problem with the transmission, such as low fluid levels, a failing transmission pump, or internal damage to the transmission components. Additionally, issues with the transmission linkage or control module could prevent the vehicle from shifting into forward gears. It's important to diagnose the issue thoroughly, as continuing to drive the vehicle in this condition can lead to further damage.