Optional 4-Hi TOD conversion using a hazard (4-way flashers) switch
you wish your TOD equipped Trooper had a full-time 4-HI option?
TOD not working due to a bad transfer case speed sensor?
Here's a fix.
One of my transfer case speed sensors failed
and shorted, thus preventing the TOD system from sensing speed and
activating power to the front wheels. Everything engages fine,
but the "CHECK" light flashes at all times and no power goes to the front wheels.
This modification allows me to use 4HI and ignore the TOD
functionality. There are other causes for the TOD "CHECK"
failure that this modification will not work around. I would
prefer to also fix my TOD system, but the speed sensors and
installation costs are prohibitively expensive.
This modification is based off of the Planetisuzoo.com article entitled "4-HI conversion for TOD equipped Isuzus".
The link takes you to an archive.org copy of the article, as it
is currently inaccessible on the web site, or has been removed.
Please read and study that article carefully, then consider this
as a replacement for the relay and switch in that article. This
does not incorporate any of the "switch sequence change" section at the
bottom of that article - either be very careful to engage TOD before
engaging this switch, or use the part of the article above to control
the 12v + line coming into the switch via LT GRN/BLK per the diagram
As with anything like this, continue at your own risk.
If you harm up your Trooper in any way, shape, or form...don't
Per the article above, you will need a fuse holder and
10 amp fuse, along with two 10 ohm 10 watt resistors. Instead of
the project box, relay, and 4HI Switch, you will need a hazard switch
from a donor vehicle - it will take the place of the relay. Ebay
or a junkyard is probably your best bet, but the switch you get MUST
have the wiring and plug included, otherwise, you will have no way to
connect everything to the switch, much less know how to connect the
pins. It appears that the same switch was used from 95 or 96
through 2002, but you will need to make sure of that, though it should
be easy to tell as I recall the 92-94 hazard switch is a totally
different round button. The switch will install into the
open spot in the dash to the right of the existing hazard switch and
4WD AUTO button. I have not yet figured out how best to do it,
but it would be advisable to label the new 4-HI "hazard" switch so you
can tell it apart from the real hazard/4-way flasher switch. You
will need to find a way to feed the completed assembly up into the
dash, or perhaps easier, just remove the dash trim to install it.
That will require removing the center forward console trim (see notes in the Brake Controller Installation
page for some notes on removing it), then the trim
around the radio, and up into the rest of the dash. It's a bit of
a pain, but not terrible, then you can easily route the wires
under the center
console to under the passenger seat, as well as tap the cigarette
lighter power outlet or other 12v + and - source. Our Trooper is
wired for a trailer brake control, so I tapped off of those lines.
This is a
scanned image of a section of the service manual that shows the wiring
diagram of the hazard switch. I tested the switch and it appears
to be a "break before make" type switch, so there should be no shorting
as it turns on and off. The text in RED is my notes. If you
follow it through logically, it should make sense, but I'll try to
the passenger seat, as noted in the article referenced above, is a wire
that goes from the TOD ECU to the clutch solenoid in the transfer case.
Two wires will need to be run from there to this new dash switch.
The wire coming from the TOD ECU connects to the BLK/RED wire and
the wire going to the clutch solenoid connects to both PNK/BLK and
RED/BLK. I chose to cut the wire under the seat and attach a male
spade lug to one side, and a female to the other (be sure to get the
type that has a plastic/rubber surround to prevent shorting).
This would allow the modification to be removed if desired, and
the wires simply connected back together.
In the off position,
nothing has changed from the original factory wiring. The signal
from the TOD ECU comes in via BLK/RED and goes out to the clutch
solenoid via RED/BLK (which is tied to PNK/BLK and as you can see, does
nothing in the off position).
In the on position, everything changes:
connection to the TOD ECU switches to connect it to GRN/ORN which
routes through the resisor pack and then to ground, which fools the TOD
ECU into thinking everything is just fine, so no errors will appear
because of the modification. Please note that the two resistors
are wired in series - GRN/ORN switch lead to the first resistor,
through it to the second resistor, through it and then to ground.
--The 12v + coming in via LT
GRN/BLK is now connected to RED/BLK and PNK/BLK, which sends 12v to to
the clutch solenoid and locks the transfer case into a 50/50 power
split and a full-time 4-HI configuration.
--Lastly, 12v + coming in
via LT GRN/BLK also routes to GRN/BLK which connects back to the switch
to RED/GRN, which illuminates the light inside the switch. This
is of course optional, and largely useless during daytime. At
night, you will see the switch illuminated when it is turned on.
I would suggest taking the switch apart to access the bulb, then
the red rubber covering over the bulb. This will make it glow
even though the switch marking is red (yes, I know, you would think it
would shine red anyway, but it comes through white), thus making it
easier to differentiate from the "real" hazard switch in the dark.
side discussion and thoughts: The switch I acquired had a bad
bulb in it, and thus would not illuminate. Being a very odd bulb,
I was unable to find a replacement in short order, though I did later
find suitable replacements available online. If you search for
"3mm twist bulb", that should put you on the right track. That
may not be the right size, but you can start there if have one in your
hand (I currently do not)...if you find the right thing, let me know
and I'll update this page. With a little work and
a resistor, I was able to replace the bulb with a small white LED out
of an odd set of LED christmas lights. If you want to try this
route, I can get you the info (or I may update this page to include
it), and may even be able to help you out with an LED, if I can find
the extras I have. It wouldn't be so easy to just purchase a
plain LED as you would need plain flexible wires to connect through the
bulb base, which this light set already had soldered to the LED leads.
What I wrote there may not make any sense until you take one
apart and see how the bulb plugs in via an odd twist-lock type base.
Another option would be to tap the 12v + illumination line from
the other adjacent buttons (I think that would be GRN/RED per the
wiring diagrams, but you would need to confirm) such that it
illuminates whenver the headlights are on, but then you have no
indication that the 4HI mod is engaged. To match the positive and
negative on the illumination on the switch to be the same polarity as
others dash lights, you may need to reverse RED/GRN and GRN/RED
from how I have laid it out in the diagram. With an incandescent
it doesn't really matter which connection is positive or negative, you
can switch RED/GRN and GRN/RED in the above diagram as either will
work. LED's are sensitive to polarity and must be connected the
right direction...if you go that route, hook it up and test before
putting the dash back together in case you wired it up backwards!
an image of the installed switch. The hazard switch to the right
of the 4WD AUTO is the "4-HI" switch that I added. On mine, there
is also a blank to the right of the clock that could be used instead,
if so desired.
is the wiring under the passenger seat. You can see the TOD ECU
on the right, and the spade connectors I added in on the left.
The orange and blue wires are the ones I added to go to the
switch. Flaps of carpet normally cover this up, so it should be
pretty much it. I hooked the wires all up, then used zip ties and
electrical tape to hold them together with the resistor packs all in a
bundle behind the dash and switch. Sorry, I did not take photos
when I put it together several years ago. You will have four
coming out of it, one to positive 12v, one to ground (negative), one to
the ECU, and one to
the clutch solenoid. I would like to find an easier way to do the
"switch sequence change" as noted in the referenced article to prevent
incorrect activation of the 4-HI modification, but I've not yet taken
the time to figure it out or implement it. Long ago, I read
something referencing another connection to do the job coming from a
positive voltage source, I think having to do with a 4-Low indicator,
but I don't recall the details and can't seem
to find it again. If you have any suggestions, I would love to
Any questions/suggestions/additions/corrections/etc, please contact me at firstname.lastname@example.org.
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