Firewall Wiring and Heater Hose Cleanup

TLDR

• Rebuilt the ground lug
• Organized wires
• Connected Regulator A ground wires
• Adjusted heater hose to length

Details

Today I spent much of the time to clean up miscellaneous firewall items before hanging the engine.

Grounding Lug and wires

Previously I had 2 grounding lugs on the firewall, one near the battery and the other near the Rotax fusebox. After reading a lot of comments from rotax-owner and Sling’s builder Facebook group, I decided to move everything to a single grounding point to avoid weird grounding issues in the future.

So the plan is to route everything to the lug near the battery. Some wires were too short, so I bought some 14GA wires from Aircraft Spruce and will rebuild those wires when my order arrive. I decided to use adel clamps to secure the wires along the route.

I removed the the few connections going to the fusebox grounding lug. The hole was pretty big, so I installed an M5 rivnut (instead of my usual M4) to cover the hole.

Then I started to route the wires, and installed more M4 rivnuts along the way, until the reached the lug.

While I was doing that, I had to undo the bundle near RE1/RE2 connectors, and re-organized them to make everything neat.

Regulator A Grounding Wires

Two of the wires I routed was for the Regulator A (EMS ground). I crimped them with ring terminals, and connected them to the regulator A’s grounding plate. I did not torque them though. I will need to unscrew the connection when install the Rotax harness in a few days.

Heater Hose and Firewall Pass-Through

Basically I missed a step on the KAI when installing the heater hose. I forgot to cut the hose to length and install the hose connection. The good thing is that the job was pretty straightforward. I just used a craft knife to cut the silicone coolant hose to be about 5 inches longer than the firewall and that was it. I inserted the pipe connector for a test fit, which seemed ok.

However, since Sling keeps changing their heater’s installation, my firewall’s holes are not pre-drilled to match the two coolant hoses. Instead, one of the holes were way too big.

So I decided to make a patch plate with the proper sized hole. The plate was about 2.5 X 2.5 inches square, and I cut a 32mm hole using the hole puncher. Then I riveted the plate to the firewall to let the hose go through it with a properly sized hole. The hole’s diameter was a few mm larger, so I bought a few rubber grommet to fill the gap. I will install them when the grommets arrive.