1998 grand cherokee, 4.0. my buddies gf said her mechanic needed a starter, so i put it in for them. nothing. dont even hear it engage. the battery was tested and its good. i switched the gear lever, nothing. i got under there, to see if there was voltage, and there is. but then while in the process, while poking, it almost started. im certain i didnt jump the terminals. any ideas? could the new starter be bad? do they need new wiring like other posts say? its just confusing me. anything will help.

 

jump the terminals on the starter solenoid. verify wiring to solenoid is engaging the solenoid. (the smaller wire or wires)

 

It could be an issue with the starter relay, the relay circuit, the neutral safety switch, or the ignition switch IMO.
From the ZJ Factory Service Manual:

DIAGNOSIS AND TESTING

RELAY TEST
The starter relay is located in the Power Distribution
Center (PDC) in the engine compartment. Refer
to the PDC label for starter relay identification and
location.
Remove the starter relay from the PDC as
described in this group to perform the following tests:
(1) A relay in the de-energized position should
have continuity between terminals 87A and 30, and
no continuity between terminals 87 and 30. If OK, go
to Step 2. If not OK, replace the faulty relay.
(2) Resistance between terminals 85 and 86 (electromagnet)
should be 75 6 5 ohms. If OK, go to Step
3. If not OK, replace the faulty relay.
(3) Connect a battery to terminals 85 and 86.
There should now be continuity between terminals
30 and 87, and no continuity between terminals 87A
and 30. If OK, see the Relay Circuit Test procedure
in this group. If not OK, replace the faulty relay.

RELAY CIRCUIT TEST
(1) The relay common feed terminal cavity (30) is
connected to battery voltage and should be hot at all
times. If OK, go to Step 2. If not OK, repair the open
circuit to the PDC fuse as required.
(2) The relay normally closed terminal (87A) is
connected to terminal 30 in the de-energized position,
but is not used for this application. Go to Step 3.
(3) The relay normally open terminal (87) is connected
to the common feed terminal (30) in the energized
position. This terminal supplies battery voltage
to the starter solenoid field coils. There should be
continuity between the cavity for relay terminal 87
and the starter solenoid terminal at all times. If OK,
go to Step 4. If not OK, repair the open circuit to the
starter solenoid as required.
(4) The coil battery terminal (86) is connected to
the electromagnet in the relay. It is energized when
the ignition switch is held in the Start position. On
vehicles with a manual transmission, the clutch
pedal must be fully depressed for this test. Check for
battery voltage at the cavity for relay terminal 86
with the ignition switch in the Start position, and no
voltage when the ignition switch is released to the
On position. If OK, go to Step 5. If not OK with an
automatic transmission, check for an open or short
circuit to the ignition switch and repair, if required.
If the circuit to the ignition switch is OK, see the
Ignition Switch Test procedure in this group. If not
OK with a manual transmission, check the circuit
between the relay and the clutch pedal position
switch for an open or a short. If the circuit is OK, see
the Clutch Pedal Position Switch Test procedure in
this group.
(5) The coil ground terminal (85) is connected to
the electromagnet in the relay. On vehicles with an
automatic transmission, it is grounded through the
park/neutral position switch only when the gearshift
selector lever is in the Park or Neutral positions. On
vehicles with a manual transmission, it is grounded
at all times. Check for continuity to ground at the
cavity for relay terminal 85. If not OK with an automatic
transmission, check for an open or short circuit
to the park/neutral position switch and repair, if
required. If the circuit is OK, see the Park/Neutral
Position Switch Test procedure in this group. If not
OK with a manual transmission, repair the circuit to
ground as required.

PARK/NEUTRAL POSITION SWITCH TEST
(1) Place the transmission gear selector lever in
the Park position.
(2) Disconnect and isolate the battery negative
cable.
(3) Raise and support the vehicle.
(4) Unplug the park/neutral position switch wire
harness connector.
(5) Check for continuity between the center switch
terminal and a good chassis ground. There should be
continuity. If OK, go to Step 6. If not OK, replace the
faulty switch.
(6) Move the transmission gear selector lever to
the Reverse position and check for continuity
between the center switch terminal and a good chassis
ground. There should be no continuity. If not OK,
replace the faulty switch.

IGNITION SWITCH TEST
WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS,
REFER TO GROUP 8M - PASSIVE
RESTRAINT SYSTEMS BEFORE ATTEMPTING
STEERING WHEEL, STEERING COLUMN, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS
COULD RESULT IN ACCIDENTAL AIRBAG
DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the steering column shrouds and
unplug the ignition switch wire harness connector.
Refer to Group 8D - Ignition Systems for the procedures.
(3) With the ignition switch in the On position,
check for continuity between the two fused B(+) terminals
of the ignition switch (terminals 1 and 7).
These are the terminals at each end of the switch
connector receptacle. There should be no continuity.
If OK, go to Step 4. If not OK, replace the faulty
switch.
(4) With the ignition switch held in the Start position,
check for continuity between the two fused B(+)
terminals of the ignition switch (terminals 1 and 7).
There should now be continuity. If not OK, replace
the faulty switch.

 

Before you start doing lots of testing, do this test first. Disconnect the solenoid trigger wire at the starter. This is the small wire. Connect a test light or volt meter to that wire. Have a helper turn the key to start while you watch the light or meter. You should see the light turn on or read battery voltage each time the key is turned to start. If this test is ok then the relay, wiring, ign switch and NSS are ok.

The problem would then be the starter, battery or cables.

When you turn the key to start, the trigger circuit sends battery power to the solenoid. The solenoid, which is an electromagnetic switch, activates and pulls a plunger to make contact between the battery terminal at the solenoid and the starter terminal. This action engages the starter and turns on the starter motor.

When electrically testing the starter, you will always have voltage at the battery cable terminal on the solenoid. You will have voltage at the small solenoid wire ONLY when the key is held to start.

Always use caution when doing these tests.

 

I am new here and I am wondering if the ignition switch could be my problem. I replaced the fuel pump. NOT my problem mine was OK. I had problems with the NSS I put in a push button jumper but have not had to use it for a long time. Does the ignition switch turn off the electrical to the plugs? I jumped the fuel pump for always on and it still will not start. Does it turn off the injectors?