Installing a mando 3 wire alt in my boat. has a volvo penta four cyl. Replacing a old motorola. I wire goes to battery. Purple wire is excitation, goes to icnitin switch. The red sensor wire goes to ?. What i see it goes to the battery +. Asked a mechanic he said is a + wire but needs a diode so power only runs one way. I dont know. Can any body help here. Thanks alot.
