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What is this bulb for?

While looking for the spare wires under the dash I did find this --- its just a bulb in a socket --- any idea what its for?
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Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: What is this bulb for?

Reply #1 –
Off topic but - Larry when you get a chance after you get your 2014 Cherokee set up for towing, please post on your experiences.  We too are looking at the new Cherokee for a towed.  Thanks in advance.

And now back to the mystery bulb...
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Mark & Mary Benko
Former coach: 2005 U295 3823
Jeep Cherokee, Honda Fit

Re: What is this bulb for?

Reply #2 –
Larry, Don't know what that bulb is but I have one too.  I was embarrassed to ask so I have just lived with it knowing that someone was ask for me . ;D
Gary B

Re: What is this bulb for?

Reply #3 –
When you flip the engine or transmission switch about a foot toward the front, it blinks the fault codes. There are two of them, with labels.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: What is this bulb for?

Reply #4 –
Quote
When you flip the engine or transmission switch about a foot toward the front, it blinks the fault codes. There are two of them, with labels.

Not sure what you mean by flip a switch about a foot forward.  Also no label, what fault codes?  Transmission codes like the ones that blink on the transmission indicator?
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: What is this bulb for?

Reply #5 –
On mine there are several of them behind the dash.  They light up with the ignition switch and most stay on.  I have never been able to find sockets for them.  Total mystery.

Keith
Keith, Joyce & Smokey the Australian Cattle Dog
1995 U320 SE Extreme 40' WTBI Build # 4780, with a Honda CR-V hopefully still following behind.
Motorcade # 17030
FMCA # F422159

Re: What is this bulb for?

Reply #6 –
I have four of them on the 95.
jor
93 225
95 300
97 270
99 320

Re: What is this bulb for?

Reply #7 –
Each year and model has different ways to read fault codes. On our 1993 U300 they are as pictured below. There are two bulbs. When the  key is turned to the run position, they light up for about 5 seconds and then shut off. If the key is left in the run position and either the engine or the transmission rocker switch is moved to the on position, the bare bulb will flash any stored code. The code descriptions are online or in our forum archives. The attached PDF is for Detroit 2 cycle codes only. 

No real need to buy a code reader as it only takes counting the flashes and writing them down. If, for example, the hydraulic pump belt breaks, the engine gets hot and the computer goes into shut down mode, it will store a code or even several codes in it's memory. Best to have someone with you with a pencil to write them down as you read them when they blink as it's easy to miss one. They are two digit with a couple of seconds between codes. Example: fault code 52 would see five quick blinks followed immediately by two quick blinks and then a two second or so break before the next stored code.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: What is this bulb for?

Reply #8 –
Thanks much ---- don't seem to have the engine/transmission switches on my '04 so the bulb setup must work differently, but the mystery is solved.
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: What is this bulb for?

Reply #9 –
Larry,

Yours probably has the same capability but just does it in a different way, possibly on a digital readout on your transmission keypad. A search of our forum archives or an Allison or Cummins forum may have the answer. A call into Foretravel will definitely solve the mystery.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: What is this bulb for?

Reply #10 –
Hi Larry,

We hope you folks are doing well.  I have no idea about the lights under the dash, just thought I would say Hi.  I have to go in search of the "Blue Module" since it quit sending signals to my air pressure gauges.  It nothing else I need to disconnect the annunciator.  I'm starting to hear dinging at night.

Roger and Susan
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: What is this bulb for?

Reply #11 –
Forgot to attach the Allison MTB-746 codes. The engine should be running when you check the transmission codes. Non MTB-746 codes may be some of the same but do a Google search. These codes are stored in a non volatile memory so can't get lost changing batteries, etc. Only way to remove them is with a DDEC or Allison tool at a shop unless you have the factory reader.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: What is this bulb for?

Reply #12 –
Thanks again for the info on the checks ---- I know the transmission does read it out it's codes right on the transmission shift light.  The bulb must be for the engine.  Never had any service people check it because they read codes through the connector on the side panel.  It may be the bulb is redundant on my year coach.

Hi back to you Roger.  One of the first mods I did was to put a switch in line with the annunciator.  It's just a very simple on off in series with one leg mounted low on the dashboard so it isn't noticeable.    Comes in handy to turn off the turn signal chime while waiting to turn at long traffic lights. ^.^d
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: What is this bulb for?

Reply #13 –
To continue on the bulbs and switches topic, I took a look inside my dash today and see that I have five of these bulbs. I found a schematic that describes them as "added resistor lights." Four for a Cat and five for a Cummins (I have the Cummins). They interrupt the wires to the CEL, Trans Temp, ABS, Eng Shutdown and Stop Eng.

Now, it gets interesting. Two of these lights are controlled by the on-off rocker. Those two run to the Stop Engine Light and the Check Engine Light. They light up along with the other three when the key is turned on. Then they turn off and illuminate again when the rocker is switched on. On another schematic, these rockers are shown as "diagnostic." One is an off-on switch and the other is a momentary switch meant to increment one way and decrement the other. I don't have any codes stored (per VMS) so I can't tell if they are working as they should.

So I have five resistor lights, two of which are apparently engine diagnostics. I have two rocker switches, one turning on the diagnostic function and the other presumably switching through the stored codes.

Here's a photo of the schematic and of my two switches.
jor
93 225
95 300
97 270
99 320

Re: What is this bulb for?

Reply #14 –
Jor,

Thank you for posting this.  Did not have that diagram in my files.  Mystery solved.


Keith
Keith, Joyce & Smokey the Australian Cattle Dog
1995 U320 SE Extreme 40' WTBI Build # 4780, with a Honda CR-V hopefully still following behind.
Motorcade # 17030
FMCA # F422159
 

Re: What is this bulb for?

Reply #15 –
Larry,

Pulled apart the dash cover, sort of an act of faith, but easier than I expected, found the dinging annunciator (the volume on mine is mechanically adjustable) and put in a switch to shut it off.  Now all I have to do is find the Blue Module.  Well, that is not really all I have to do.
 
Working our way across N Florida heading for SC.

Roger
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN