Ripper is on the money here - your plan should be OK. FYI, I recall measuring 3,9ohms through the starter solenoid control circuit, which gives a 3-amp load on the wires. Something to think about in case you have very thin wiring for the idiot light. The 0,5mm2 wires that go into the switch itself should handle it, though.
Having done the m-Unit works with full safety circuit, I completely understand why so many want to skip it. The safety features probably double the amount of wire and adds an extra relay. However, with everything in place, I’m really happy to have it. I think the simple splice you’re doing here is a mod with one of the best safety/hassle ratios.