It is relay EO8 in the diagram. Location is in underhood fuse box as you mentioned.
I just remembered 2 other possible causes.
If the antitheft system is non factory, it is possible the alarm control unit is linked to the lights directly and bypassing the taillight relay. If it is faulty, it can cause the problem. For factory system it would not occur as the system needs the taillight relay to work.
The other possibility would be a wiring fault. The light wires have been fused to a power supply possibly due to a shorting and overheating has caused the wires coverings to melt.
Tuesday, August 24th, 2010 AT 6:40 AM