Service 4WD light comes on when I switch AUX light on

Carolina_Jake

Original poster
Member
Jun 7, 2013
28
I have searched until my hands are tired.... And no answers. The situation is like so, I haven't installed or changed anything in a few weeks now and the alarm light has just started yesterday. I've tried every situation and combination of lights and switches and nothing else set the alarm light on but the roof top KC Lights. I've had these installed for sometime now and I've had no problems until now. I can reset the "SERVICE 4WD" light by unhooking neg battery cable a few secs. Any ideas? Thanks in advance any/everyone
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
I don't think anybody ever had this exact problem, so I'm not surprised your search was fruitless. So let's troubleshoot it. :yes:

The "service 4WD" light comes on if the TCCM doesn't see the sensor feedback voltages it expects from the encoder motor or the front axle actuator. OR if the PCM loses communication with the TCCM.

What happens when you turn your AUX lights on, assuming they are incandescent lamps, is a huge inrush of current that can induce current in any wires running parallel to the power OR ground wires, and also develop a voltage on the ground lug of wherever the aux lights are connected to.

My guess is that surge current is upsetting the TCCM and causing it to quit talking to the PCM.

Can you describe fully how your aux lights are wired? Are you using a relay? Where is the switch? Where does the power come from? What path does the wiring take from the battery to the lights? All the wiring, even the ground. Are you sharing the power or ground connections with any other connections or ring lugs?

I suspect your fix will be just changing the path of the wiring, the tightness of the connections, or something of that nature. I'm working on a test system where I need to accurately measure a 500 Amp pulse, 100 billionths of a second wide (100 nS), without touching the current path because it may have 600 volts on it. So I'm depending on the crosstalk (induced current) from that 500 Amp path to a small inductive loop of wire (embedded in a PCB, actually) placed 0.003" away. We're getting about a 3 volt signal induced in the small loop, and that's very easy to measure with a high speed digitizer.
 

Carolina_Jake

Original poster
Member
Jun 7, 2013
28
Yep that's right they are incandescent, I have 6 total. The 2 round KC on brush guard, and 4 rectangle on roof rack. The 4 on roof rack is where the problem comes in, they set off the alarm. I can run the front 2 as long as wanted. As soon as the 4 on top are on with or without the front 2 on , the alarm shows.
They are wired as so : front 2 on factory relay and wiring to single switch.
Top 4 on factory relay and wiring to single switch.
All the white load wiring is connected directly connected to positive post of fuse box and ground is connected to raw threaded spot on chassis. Then threaded thru firewall for switches.


One more thing.... I've had this setup for about 4 months now...nothing has changed nor have I added any wiring else where. It just started out of the blue... :confused: and it has always performed great. Search and rescue numerous times for hours at night, rain and hard conditions.
 

The_Roadie

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Member
Nov 19, 2011
9,957
Portland, OR
Thanks for the details. Wiring crosstalk can be marginal on a good day, and when the connections or the lamps age, the inrush current changes and the issues become apparent.

What factory relay are you using for roof lights? I know there's a fog lamp relay you can repurpose up front, but what about the roof? Where is the relay exactly?

Try removing one or two lamps up top to prove it's inrush current that's the root cause. Then move the wires around that are going through the firewall. To reduce external crosstalk to a minimum, you want to run the power and grounds right next to each other and as tightly coupled as possible. Tape them together if you can. If they are separated, that allows more induction into oehte riwing, especially ones that end up between the outbound and inbound current.

If the problem happens more when you turn the relay OFF than when you turn it ON, I have another suggested fix of a diode wired across the relay coil. That would suggest the problem is induction from the switch wiring instead of the power wiring, but that's a lesser probability.
 

Carolina_Jake

Original poster
Member
Jun 7, 2013
28
I should've worded it better for ya, but the factory wiring and relay I used was the KC Light's factory hardware. 2 Lights (1 set, 1 relay) in front on brush guard, and 4 Light (2 sets, 2 relays) on roof top (wired on 1 switch). So 2 switches control 6 total lights. Switches are located on OEM light switch panel (vertical blank panel)

Another Note: Right before all this started I notice the NEGATIVE TERMINAL was very HOT, (I was just doing routine checks and battery terminals I always check for to be loose or corroded) So i tried tightening it up, which it was tight enough, so I moved on, later checking again and it was no longer hot.


Im sorry I've got to explain and describe all of this in lamens terms, Im not too good at the technical terms of the electric world :mad:

ADDITIONAL NOTE: Right after our first talk I went to AutoZone and got a " side post extended post " Gold Plated ohhh I got fancy there :biggrin:
From there I re-attached all of the KC Lights white (hot) wire to this nice and fancy gold plated terminal bolt extender
View attachment 29704

And a short test drive later the light came back on but only after a longer ride, maybe 15 mins of constant ON then a few times switching on and off the light came on when it was switched to the ON position....
Im trying to think if there are anymore details and if ya need more info just let me know....I'll damn sure try :stars:
 

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The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Your switches are located very close to the TCCM. Many folks put them in the overhead console. I'm still suspicious about the TCCM getting influenced by a spike on the control switch wiring. Can you see how the wires are routed and move them away from the TCCM?

Also, where are the relays physically located? And what wiring harnesses are the relay wires near? And how does the power wiring get from the relays to the roof?

And can you try the "removing 2 lamps" experiment?
 

Carolina_Jake

Original poster
Member
Jun 7, 2013
28
Thanks for the info Roadie ,
Ive moved my switches away from the transfer case control module, and placed them on the inside of my center console(arm rest). I know it sounds like a far off spot for them but I had to find a place that my little man, 3 year old replica of me , could NOT explore and play with too much.

The light has not come back for 2 days now and Ive been on several night calls and used the lights extremly hard. So thanks for the info on the topic...

Now for another topic... I go tomorrow for my PCM tune up at PCM of NC... Some good folks there but Im getting alot of overheating issues in the past week or so, should i get an E-FAN or no?

Another topic in another section of forum , I know..... headed there now
 

Carolina_Jake

Original poster
Member
Jun 7, 2013
28
Did i really? I didnt even notice bud, sorry about that... I tried about 10 different ones i wanted and that one was the only to fit into the pixel restriction/sizing ;( Give me a lil bit to alter some .jpg of mine to the pixel sizes needed and i'll switch it up.

View attachment 29803

Im kinda getting tuned up .... 2pm appt. :cool:
 

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