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Harrison Fire
Senior Member
United States
175 Posts |
 Posted - 03/19/2011 : 12:32:17 PM
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Before the morning run (zero-dark-thirty hours) a bus was brought to me with a tail light out. The problem appeared to be a burnt out bulb. Changing the bulb did not bring satisfaction. It appeared that the contacts had either worn or deformed causing the running light side to not make contact to the 1157 bulb. It would stay lit if pushed to the side. The brake light worked right along. Normally, I would change the light assembly at this point and send the victim on it's way. One problem. This is a C-2. The entire pod, a one piece affair, is glued into place with no provision to reach the wiring. After some test prying and several loud cracks, I decided to get a replacement light before the next removal attempt.
Out came the pick to bring the socket contacts closer to the bulbs contacts. This may have made things worse. A direct short was created with the pick. No power to that circuit only. No fuses tripped/blown. Just a blinking drivers monitor for that light. Any ideas?
Handy VIN # CW26223
HF |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 03/19/2011 : 8:04:03 PM
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Did a code pop up on the dash when your pick grounded out the circuit?
Did power return after cycling the key off for while?
I'm thinking that the FET saw the dead-short from the pick & shut down the output to that light. Confirm the wire continuity by establishng a consumer draw to any groud. Kevnin usually uses a headlight.
Guestimated Outputs to Lights on Similar Year Buses:
CHM Connect #4 Pin C (Left)
CHM Connect #4 Pin L (Right)
SHM Connect #2 Pin E (Left Lower)
SHM Connect #2 Pin F (Right Lower)
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I may not know the answer but I can usually find who does. |
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Harrison Fire
Senior Member
United States
175 Posts |
Posted - 03/20/2011 : 5:42:07 PM
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The biggest shock for me was the realization that each tail lamp has it's own wire running to the front. Are the brake lamps wired the same. Or did I miss something?
Sorry Justin. I did not look at the dash for codes. Kevin is coming on Tuesday to change an EGR valve on one of the Mercedes 906s. (Always go for longest warranty you can buy, it will pay for itself) So, when the FET (Whaatt?) senses a direct short to ground, it changes from positive to negative? Didn't cycle the key but did remove all the connections to the left CHM (the one underneath the bus, coated with greasy mud) and the power came back, at about half brightness, then went away again. Working a one man shop, I run out of time to figure out fun stuff like this. I have the wiring drawings, but did not quickly find the CHM on them. Saw Tom Wilkins' phone number on them. If I had more time, he would have gotten a call. And Kevin did show me the headlight trick. Thanks for helping Justin.
HF |
My Fleet? (6) 93/99 IH 3800 Thomas and Blue Bird, Hydraulic Brakes, Manual and Auto Trans, (10) 00/06 FS65 Thomas Air Brake and Auto Trans, (2) 06 C2 Thomas and (2) 09/10 IC CE 300, Plus 3 more from another District |
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IBTMech
Top Member
USA
973 Posts |
Posted - 03/20/2011 : 6:18:13 PM
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| Are the C2s multiplexed? Sorry, I have no experience with C2s. ICs and BBs, yes. |
If it doesn't fit, FORCE it.
If it breaks, well, it needed replacing anyway.
Pullin' wrenches for 45 years. |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 03/20/2011 : 7:14:54 PM
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On an output to consumer circuit like a tail-light, you can unplug the harnesses that I referenced for you. From that plug & pin to tail-light (consumer) to ground is a good old fashioned tail-light circuit.
For diagrams look at the CD I loaded onto your shop PC:
Thomas Shop Resources/C2 Electrical References/C2 Drawings Not VIN Specific/103972Wiring rrStopTailTurn Lights
The FET (Field Effect Transitstor) is the switch/fuse/relay for each pin sending power out of a module to a consumer. FETs are a glorified diode that is printed the module circuit panel just before the pin goes out to the connector. The FET monitors amperage & if the amperage exceeds what thast circuit is programmed to carry, the FET will then break that circuit & throw a code to the dash.
If you suspect a consumer (ie tail light) wire, you can:
1. Unplug that harness from the module
2. Unplug the other end from your consumer
3. Establish a strong (ie headlight) consumer & a ground (ie gator clip to chassis) at the consumer end
4. Send power to the high draw test consumer.
....a. if it lights up well, check the original consumer & also check the consumer ground circuit.
....b. If it doesn't light up well, look for the smoke or pin in a new wire from the module connector pin-out to the consumer (Overlay in Kevin speak)or look elsewhere. |
I may not know the answer but I can usually find who does. |
Edited by - JustinB on 03/20/2011 7:21:14 PM |
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Harrison Fire
Senior Member
United States
175 Posts |
Posted - 03/26/2011 : 03:33:23 AM
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quote:
Originally posted by IBTMech
Are the C2s multiplexed?
Yes they are. One selling feature was "Less wiring".
From what I have seen, just the opposite is true.
quote:
Originally posted by Harrison Fire
----- It would stay lit if pushed to the side. ---- Normally, I would change the light assembly at this point and send the victim on it's way. ---- and the power came back, at about half brightness, then went away again.
Mystery solved.
Broke the light pod while carefully trying to remove it. With it out of the way the cut wire insulation with corroded copper was visible.
Got the updated replacement lights. A flat metal plate with 3 holes for the separate, sealed and weather packed lights. No way to change the bulbs so one of each was ordered for stock.
No dash codes showing - a direct short fried the bad spot in the wire till I wiggled it.
I found the wiring info that you described, Justin, on a CD. (nothing loaded to HD) The 2 wires for the left running light are sliced together just after leaving the CHM, in the wiring diagrams (overlays?).
And thank you Justin.
Are you actively looking?
3rd shift is the pits.
HF |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 03/26/2011 : 7:55:39 PM
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quote:
Originally posted by Harrison Fire
And thank you Justin.
a.) Are you actively looking?
b.) 3rd shift is the pits.
HF
I'm glad it worked out. 
a.) Yes. Ahem, let me clarify this: YES!!! 
....still doing some consulting/training/Diag computer setup on the side too. Monday AMs seem to work out well.
b.) Worse than that - 2nd shift 4pm-2:30am + 1-9:30 on many Saturdays. I don't see the 8 & 12 y/o sons from Sunday night until Saturday morning. I'd prefer 3rd shift. |
I may not know the answer but I can usually find who does. |
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Topic |
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C-2 Mystery
