If you have not yet done so, I think it would be very helpful to download the ICS Technical Manual (
https://www.manualslib.com/manual/14736 ... l-Ics.html) as well as the C300 Service Manual (
http://permobilus.com/wp-content/uploads/2016/11/45.pdf).
In the C300 Service Manual, you will find a layout of the major control components on pages 66 and 67. This will give you an idea of what components are in your system and how they are connected together. It does not show you where they are physically located on your wheelchair, through. For that, you will need to see page 37 (presuming you have an RNet system) for the power module and page 41 for the ICS master control module.
This service manual is for a more recent version of your chair, so there could be a few differences. It is possible your chair is old enough to have a VR2 rather than an RNet system. If so, the Service Manual I linked also covers the VR2 components, though in a bit less detail.
To find how to disconnect the cable for the tilt actuator, first, find the tilt actuator. Then follow its cable back to where it plugs into something. It will probably not plug directly into the Power Module. That is because RNet uses a bus. So, there will typically be a cable from the power module to a junction box. The actuator cables are then plugged into the junction box. Simply unplug the cable going to the tilt actuator from that junction box. After doing that, cycle power a couple of times and things might work OK. Rnet is set up to automatically detect and handle configuration changes. It usually does this OK, but there have been times I have had to tell it what to do. If that is necessary, it can often by done by manipulating the buttons on the ICS control (often mounted just behind the joystick module). The ICS Technical Manual explains how to do this.
If this all works, it would point to a bad tilt actuator. In that case, you can often find used actuators on ebay for a reasonable price. Be sure to get one that exactly matches the numbers on your current tilt actuator.
If this does not work, it likely points to something else being a problem, such as one or more cables, the junction box, the ICS Master Module, or the ICS control panel. Of these, I have had failures in an actuator, an ICS Master Module, an RNet cable, and the ICS control panel. But, those are not typical failures. I use my chairs a lot and sometimes in really bad weather.
It is all amazingly simple once you take a few parts off your chair. The Service Manual will show you exactly how to remove those parts.
I know you will not be doing the work yourself, but having an understanding of the layout of the components in your chair will be invaluable to you as you guide other people while they do the work.
And, as I have said before, the first thing I would do would be to inspect all the RNet cables and connections and use an electronic contact cleaner to clean the connections.
Steve