I didn't tap into the SRS wiring. The factory radio harness and SRS system work off of the same fuse. When the aftermarket radio was installed, an adapter was used that plugged directly into the Bose wiring harness. The radio and SRS worked for 4 years with no problem. I only changed the radio over to the cigarette lighter circuit so that nothing but the SRS was on the blown fuse circuit and it could be isolated from the radio.
The SRS wiring circuit has never been messed with.
I may just have to bite the bullet and take it to the dealer; at least for diagnostics.

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1985 300TDT
2013 E350 Bluetec