Hello Phil.
I know this is an (old) thread, but I just discovered it.... and if anyone else flying the Piper Archer in FS2004 wants to add strobes to your plane, it is easily done by making the needed changes in the aircraft.cfg file.
The following in an example of one of my Piper Archer installations... this one is from my laptop FS9 sim.
Carenado Piper Archer
(Please NOTE> this modified cfg. does NOT have the landing light replaced yet - ONLY the strobe lights )
[lights] //Types: 1=beacon, 2=strobe, 3=navigation, 4=cockpit, 5=landing light.0 = 3, -3.6, -18.4, 1.29, fx_navredcarenar light.1 = 3, -3.60, 18.40, 1.30, fx_navgrecarenar light.2 = 1, -17.0, 0.00, 6.18, fx_beaconcarenar light.3 = 4, -1.00, 0.00, 1.60, fx_vclight light.4 = 2, -3.80, -18.40, 1.26, FX_STROBECARENAR.............< I added this line to give strobes light.5 = 2, -3.80, 18.40, 1.26, FX_STROBECARENAR.............< I added this line to give strobes