Toyota claims that when towing a trailer if the SVC, check engine, 4LO, and anti skid warning lights come on the vehicle has experienced an excessive electrical load. Usually a fuse is also blown. The fix is an expensive wiring harness and fuse assembly. The new circuit is installed to remove some of the load from the existing 10amp circuit. The problem with this is I was towing a small trailer, minimal lights, no brakes, and this occurred. If the electrical circuit is so frail then Toyota has a design flaw that they should fix. I had the fix applied, but have not tested it yet.