Very close indeed. Except that you actually need a 2 way rocker momentary or 2 separate momentary buttons as open and close uses different polarity.
How to use 2 Aux Switch's to control the exhaust cut out.
Additional items needed to make this work
Qty 1 - Automotive 5 pole relay.
check here
Step 1. Connect AUX switch of your choice to pin 30 or the common connection on the relay.
Step 2. Connect the Power wire for the open direction to the pin 87 or the normally open on the relay
Step 3. Connect the power wire for the close direction to the 87a or normally closed on the relay.
Step 4. Connect pin 85 to the aux switch of your choice. This AUX switch will now be your open/close toggle
Step 5. Connect pin 86 to ground.
Now to open the cut out, toggle the AUX switch from Step 4 to on. This will enable opening of the cut out when the AUX switch from Step 1 is flipped. Note that partial opening can be achieved by not leaving the Aux switch on till the cut out is fully open.
To close the cut out toggle the AUX switch from step 4 to off. This will enable closing of the cut out when the AUX switch from Step 1 is flipped. And as before partial closing can be achieved.
Enjoy.