I have 3 garden tractors which have the circuit below controlling their PTO clutches. With 12V applied to the clutches thru the PTO switches, ground is applied via an interlock circuit (black box). That interlock circuitry is understood to be sensitive to having a positive voltage applied. Can someone tell me how the diodes are protecting the interlock circuit. And if they are not doing that, what their function might be? Looks like the diodes could be removed and the PTO's would function just fine. I appreciate any insight that might be given on this; I have just not been able to figure it out.