Remove two rivets from the firewall that correspond to the Starter/Master Relay attach locations. What a mess this turned out to be. Since the removed rivet locations line up with the platenut wings (where I will rivet the platenuts on the firewall), first I had to locate and drill the second rivet hole and then by clecoing the platenut on the forward side of the firewall and selecting a drill that just fit into the platenut bolt hole I drilled the bolt hole on the firewall (making sure I did not harm the platenut threads). This ensured that the bolts will fit into the platenut without offset. Then I removed the platenuts and clecoed them on the back side of the firewall and tested the bolt for easy fit. Unfortunately I had to enlarge the holes through the firewall by 1/64th to guarantee a good fit. Riveted the platenuts to the backside of the firewall. Test fit the Starter/Master Relay using the two outside bolts and marked the location of the inside bolt holes.Drilled the two 1/4" holes on the F-7127D doubler. Located and drilled the second bolt hole (1/4") for the Master Relay as per DWG 31A. Aligned the backing plate and bolted it in front of the firewall using the just drilled hole. Drilled the 4 rivet holes and clecoed everything in place. Drilled the second bolt hole for the Starter Relay. Deburred everything riveted the platenuts to the backing plate and riveted the backing plate to the back of the firewall. Installed the Starter/Master Relays. I had to trim the Master Relay bracket slightly for proper fit. Looks great, but what a back breaking work for such a seemingly simple setup.
