[Bob86ZZ4]

Are you sure you need to have those diodes to prevent current from feeding back into the other circuit? You've got the light. You feed it positive current from your switch. That current lights the bulb. That current also is going to try to flow to the reverse light switch located on the transmission. It's going to dead end there since the trans will be not in reverse. If it was in reverse the light would be on anyhow. Nothing will happen to that current anyway. Now let's look the other direction. You've got the light hooked up to both your switch circuit and the transmission reverse switch. You shift into reverse and the light comes on. That positive current will also try to flow toward your switches but won't go anywhere since the switch was off. Turn the switch on while it's in reverse and no harm will come anyway. The light will be on. That's it. The current isn't going to crash into itself and explode.

I'm not sure about how you've explained the circuit for the light/switches. Each light switch isn't really a spdt. An spdt switch has a center off position and two alternate positions that current flows to either contact when you switch it to them. You can't use a spdt switch for a three way light circuit because if you leave the switch in the center position it allows no current to flow through it at all. If that were the case no matter what position you place the other switch the light will not light. A three way light switch has a common terminal and two other terminals. The current always flows through the switch from the common to either of the switched terminals. I guess that's not completely accurate since if the light isn't burning no current is flowing. But the circuit is always connected through a three way switch from that common terminal to either of the other terminals. You start with the positive wire connected to the common on the first switch. Then you have two wires running from the other two terminals on that first switch to the two switched terminals on the other 3 way switch. Then the common terminal on that second switch is wired to the positive on that light at the end of the line. I'm guessing that's the way you've got your light wired but the way you explained it kind of confused me. But maybe the way I've explained it confused you and everybody else. I've wired lots of 3 way light circuits and that's the way I understand them.