Adding electric starter

I have a been slowly working on a 1976 kz400d cafe project and i want to put an electric starter on it. Does anyone know what i need to do to make it compatable? Any suggestions would be appreciated, thanks in advance.

The 1976 KZ400-D3 came with an electric starter as standard equipment. If yours is missing a previous owner must have removed it. If it was mine, I would start by taking an inventory of which pieces the previous owner left on the bike. The following diagram shows electric starter related parts for the 1976 KZ400-D3. You may want to use that as a checklist to see what parts are still there and which parts need to be replaced. Ed

Hopefully the starter is still intact & the po just removed the handlebar switch assy &/or wiring.
Note: the handlebar diagram may have an error in regards to the push button on the right side housing assy. The button is listed as a horn button, but there is also a horn button listed for the left housing assy. My guess is that the rt side button is for the starter.