I deducted a star for unclear/misguided instructions that could easily damage the unit. I replaced the S86F spark module, but for some reason what I had wasn't what the instructions said.1. The instructions state that you must connect an unswitched (whatever that means) transformer wire to 24V GND. Don't worry, check which wire of the 24V transformer is connected to ground (heater metal parts) and use it.2. The S86F I had didn't have the TH-W cable listed in the instructions. If you feel the same way, you should follow S90. This. Connect the 24V line and connect it to the 24V and TH-W terminals. If you don't do this, the device won't work and you might think it's broken.3. The instructions state that the spark/sensor dual wire requires the black jumper to be disconnected and cut. That is not true. Mine had a wire that doubled as a spark and flame sensor wire, and I NEED a damn jumper. Again, if you follow the instructions provided, you can assume the device is defective.4. The terminals are a quarter inch higher than the S86F I had which caused some problems getting the wires into the ignition module well (especially with the included Rajah ignition plug). My guess is that some of the 1 stars here might actually have ignition modules on them. like mine, followed the instructions and the device didn't work. Anyway, it took me a freaking hour to figure it out and lo and behold - works like a charm. I hope it will last as long as the original (15 years).