Geo tracker lights and radio not working

power loss.
any good car elect. tech find this pronto.
just takes a volt meter to find the voltage drop point.

top fails:
1: corroded fuse box on right front finder (under fuse box)
2: did you say it kills motor too. cant figure above.

what about heater fan, it uses tons of current.
as does HL followed by tails.

20amps, 15amps and 5amps respectively

you have resistance some where.
and load , kills the voltage .

for me.
i'd:
check battery voltage , when it dims out.
then of ok 12.5v is ok key on,not started.
then check voltages at a right fender , fuse panel
all points there, 12.5vdc , same as battery v.
if OK
then
check voltage at the fuse above right knee
with load full, hl, fan, brakes, just key on.

now you know what circuit is fail ing by now.

report back with this facts.