1996-1998 Grand Cherokee Fog Lamp Modification Project

1996-1998 Grand Cherokee Fog Lamp Modification.
By Scott Mueller

The stock fog lamps on the 1996 through 1998 Grand Cherokee (ZJ) work
only when the park lamps or low beam headlamps are on. When the high
beams are engaged, the fog lamps automatically turn off. The fog
lamps also turn off when the parking lamps are turned off via the
main headlamp switch. This prevents accidentally leaving the fog
lamps on even if the fog lamp switch is left in the on position.

This is accomplished via the Body Control Module (BCM) which has
control over the fog lamp relay. When you turn on the fog lamp
switch, it grounds pin A15 (BR/WT - brown w/white tracer) on the
Black BCM connector, which allows the BCM to determine that the
switch is on. The BCM then checks to see if the parking lamps are on
and the high beams are off. If both conditions are met, then the BCM
internally grounds pin B22 (DG/YL - dark green w/yellow tracer) of
the White BCM connector, which is wired to terminal 85 of the fog
lamp relay in the Junction Block. The other side of the relay coil
(terminal 86) is hot at all times, so the relay energizes and power
is then provided to the fog lamps via terminal 87 of the relay.

I have devised a simple modification which will allow the fog lamp
relay to be controlled directly by the switch, and yet also retain
the safety feature of turning off the fog lamps automatically with
the main headlamp switch. This will allow the fog lamps to operate
anytime the parking lamps are on, including when the headlamps are in
either low or high beam.

This modification can be performed such that no wires on the vehicle
are cut or spliced, the entire affair is a plug-in deal and can be
easily undone. Optionally one can choose to splice a couple wires
making the modification a little quicker and easier to perform.

There are two parts to the modification, the first involves removing
the BCM from the fog lamp circuit, by jumpering the fog lamp switch
and fog lamp relay coil ground wires together. This puts the switch
in direct control of the relay.

If you stopped at this point, the fog lamp switch will control the
relay 100% of the time, meaning anytime the switch is on, the relay
would be energized and the fog lamps would be lit. This is because
the fog lamp relay main battery terminal (30) and coil terminal (86)
are both powered from the same fused B+ circuit (Batt F62) which is
hot at all times. Some may prefer the switch to work this way, but
the danger is you could easily leave the fog lamps on as they won't
be monitored by the headlamp on warning chime, and they won't go off
even if you turn the main headlamp switch off.

The second part of the mod involves separating the fog lamp relay
coil (terminal 86) circuit from the main relay feed (terminal 30),
and providing power to the coil (terminal 86) from the parking lamp
circuit (L90) instead. This will allow the fog relay to energize only
when both the fog lamp switch is on AND the parking lamps are on.
Thus when you turn off the main headlamp (and therefore parking lamp)
switch, the fog lamps will also go off no matter what. With this
change, the fog lamps will operate only when the parking lamps are
on, which is a much more intelligent "factory" like setup.

Parts needed:

2 6" pieces of 20 ga. wire
2 6" pieces of 18 ga. wire (can also use 16 ga.)

and

1 spare Micro-Relay
-Waytek p/n 75213 - $2.7265 ea.
-Chrysler p/n 04671168 - $10.00 ea. list, $7.50 net

and

1 Micro-Relay PCB socket with terminals included
-Waytek p/n 75292 - $0.8405 ea.

or optionally

2 1/4" male spade terminals
2 3/16" male spade terminals

and

1 1/8" female spade terminal

Waytek Inc. <http://www.waytekwire.com> (800-328-2724) carries
Micro-Relays, sockets, and terminals. They have a minimum purchase of
$5.00 worth of each and a minimum purchase total of $25.

For reference there are two standards for marking relay terminals,
the numbers will be stamped or molded into the bottom near each
terminal. The following table shows a cross-reference of relay
terminal designations:

Micro Mini Circuit 
Relay Polarity Description
--------------------------------------------------
1 86 + Coil Battery (B+)
2 85 - Coil Ground - Relay control
3 30 + Common Feed (B+)
4 87a +NC Output - Normally Closed
5 87 +NO Output - Normally Open

Instructions:

The first step is to disconnect the wires from BCM A15 (fog switch
sense) and B22 (fog relay ground) and jumper them together. To do
this follow these steps:

Disconnect the battery negative cable.

Remove both switch pod bezels by using a trim stick to pry around the
perimeter of each bezel to release the snap clip retainers.

Remove the screws securing the steering column opening cover/knee
blocker. there is 1 screw on each side of the steering column, 1 on
the outboard end of the instrument panel, and 4 along the bottom edge.

Remove the steering column opening cover/knee blocker using a trim
stick to pry the edges away from the instrument panel at the 4 snap
clip retainer locations.

The BCM is mounted just below the outboard switch pod (headlamp
switch). Reach behind and unplug the black and white BCM connectors.

Option 1 (no cut wires):

Disengage the blue terminal lock tabs from each of the BCM by pushing
them in from the side of the connectors. Using a small pick,
disengage terminal A15 (BR/WT) from the black connector, and B22
(DG/YL) from the white connector. Push the lock tab back in place
after the terminal has been removed.

Note: without a special semicircular terminal pick (Chrysler special
tool 6934) you may find it easier to completely disassemble the
connectors to get the terminals out. Make sure when you reassemble
them that all the terminals go back in the correct locations and are
fully seated (except A15 and B22).

Connect the two female terminals you removed together, using a small
or thick pin as a double male connector. Seal the connection with
shrink wrap.

Option 2 (cut and splice):

Simply cut the A15 (BR/WT) and B22 (DG/YL) wires near the black and
white connectors respectively, and splice them together (seal the
splice with shrink wrap). This eliminates having to disassemble the
connectors to try and remove the terminals.

Continue:

Reconnect the black and white connectors at the BCM, and replace the
switch pod bezels and the steering column opening cover/knee blocker
if removed.

Phase 1 is now complete. If you wish the fog lamp switch to be
completely independent of all other switches and functions, you can
stop now. Anytime the fog lamp switch is depressed, the fog lamps
will be lit.

-------------------------------------------------------------------

Phase 2: The next part is to make up a relay extension connector,
powering the relay coil via the park lamp circuit.

Option 1 (more elegant method):

Take an existing micro-relay, remove the dust cover.

Carefully remove the solenoid and contacts inside the relay, leaving
only a shell with the terminals installed in the base.

Solder the 18 ga. (or 16 ga.) wires to terminals 30 and 87 inside the
relay body.

Solder one of the 20 ga. wires to terminal 85 inside the relay body.

Drill a 1/4" hole in the side of the relay cover, and slip the cover
over the three wires until it latches into place. You should now have
a plug that looks like a relay, with three wires protruding out the
side.

Option 2 (crude method):

Crimp a 1/4" male spade terminal onto one end of both 18 ga. (or 16
ga.) wires.

Crimp a 3/16" male spade terminal onto one end of one of the 20 ga.
wires.

Continue:

Solder the other ends of the wires attached to the relay base to the
same terminals in the new relay socket. The wire from terminal 30, 87
and 85 in the base should run to the same terminal positions in the
socket. If you merely used spade terminals, then solder the other
ends of the 18 ga. (or 16 ga.) wires to the terminal positions 30 and
87 in the new relay socket, and the wire with the 3/16" spade
terminal to terminal position 85 in the relay socket.

Solder the remaining 20 ga. wire to terminal 86 in the new relay
socket.

Be sure the battery negative cable is disconnected.

Remove the fuse access panel by unsnapping it from the right cowl
side kick panel.

Remove the nut that secures the right side kick panel to the junction
block stud.

Remove the 2 screws that secure the right side kick panel from the
door opening trim panel.

Unplug the fog lamp relay from the junction block.

Unplug connector C8 (yellow) from position E in the junction block.

Option 1 (no cut wires):

Locate position 9 in the yellow C8 connector, it will be the only
empty terminal position. Slip the crimped on terminal end of the wire
attached to the relay socket terminal 86 into the yellow connector at
position 9.

Crimp a 1/8" wide female spade terminal on the other end of the wire
connected to the relay socket at terminal 86.

Note: I am trying to find the exact Chrysler terminal part number
for this terminal. Until then any 1/8" wide female terminal should
work.

Reconnect the yellow C8 connector the Junction block. Insure that the
female terminal you inserted into the connector is fully seated.

Option 2 (cut and splice):

Locate the DB/RD (Dark Blue w/Red tracer) going to position 10 in the
yellow C8 connector. Splice the wire from the new relay socket
terminal position 86 to the DB/RD wire.

Continue:

Plug the relay extension harness into the fog light relay position in
the Junction Block. If you are using individual male spade terminals
rather than a connector made from a relay base, then make sure you
plug the proper spades into the proper matching terminal locations.

Plug the fog lamp relay you removed earlier into the new micro-relay
socket in your extension harness.

Reinstall the kick panel and fuse access cover.

Reconnect the battery. Turn on the park lamps and then the fog light
switch. Turn on the low beam headlights, the fog lamps should remain lit.
Finally use the dimmer switch to turn on the high beam headlamps, the fog
lamps should remain lit.

That's it! The fog lamp switch will now control the fog lamps anytime
the parking lamps are on, independent of the headlamps. Scott.