00' prizm tail light fuse blown

[yeding]

hi, guys. I have a 00' prizm. I got hit at the front left side weeks ago, after the car was fixed, I noticed that my tail light, instrument panel illumiantion, as well as the gear shift illuminaton were all off. the fuse blown, but whenever I tried to replace the fuse, it blown right away. so I think there's short circuit somewhere. Mechanic wanna charge me 300 bucks for just check it for me. so I decide to do it my self. now, the thing is: in the fuse slot, the voltage is 12 V when I turn on the combination switch, which I think is normal. but the one of the connectors in the fuse slot is grounded no matter I turn on the conbimation switch or not, the resistance between this connector to ground is always less than 1ohm. I think without the combination switch on, that connector should not be grounded, so the short circuit is somewhere between the fuse slot and the combination switch. Am I right? according to the wire diagram I found on the repaire manual, the current goes out from the battery to the TAIL RELAY, and then go through the TAIL FUSE, and split in two, one goes through the INTEGRATION RELAY and finally get into the instrument panel illumination bulb; while the other one goes to the combination switch and then to the TAIL LIGHT. My question is: does the INTEGRATION RELAY controlled by the combination switch? without the combination switch on, the current can not get into any bulbs because of the switch or the INTEGRATION RELAY, right?
sorry for typing so much...... and thx for ur attention