what engine 2.3 L 3.0 OR 4.0 L
y/w must have 12 v from starter relay to fuse box under hood to alt
check wire harness there a splice in there may be corroded also check under fuse box
there also a fusible link on starter relay Colour g/y to link then change to black an orange
lg/red go to dash Light
here a basic diagram
http://www.tffn.net/altwirng.html
w/bk from alt to inner ratifier
make sure that the starter cable alone on 1 side of relay
and Bat cable and Other fusible link are on the other side or relay
you may have a short on starter relay to switch
on those there two solenoid one on fire wall pass and one on starter
remote starter can do that to if you have one
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y/w from fuse under hood 15 amp
bk/o from link starter relay
use diagram i posted and disconnect small wire on starter solenoid see if it charge
if you need diagram for starter or alt let me know ??