Furnace keeps resetting
Check the flame sensor.  Sounds like the furnace may not be sensing that the burners are on. Also, consult the manufacturers documentation for trouble code light sequences. The flashing light might be trying to tell you something.
Unconfirmed Trane Error Codes
Codes are displayed using a light (LED) turning on a number of times, followed by a pause. For example:
._._._.___._._._.___
. = On _ = Off
Would be read as 4 flashes, and would mean that one of the limit switches was open.

Flashing Slow - Normal - No call for heat
Flashing Fast - Normal - Call for heat
2 Flashes - External lockout, retries or recycles exceeded.
3 Flashes - Pressure switch error.
4 Flashes - Open limit device.
5 Flashes - Flame sensed when no flame should be present.
6 Flashes - 120V power supply polarity reversed, or poor grounding.
7 Flashes - Gas valve circuit error.
8 Flashes - Low flame sense signal.
9 Flashes - Check igniter.