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Old 07-13-2022, 10:59 AM   #1
Junior Member
Join Date: Jul 2022
Posts: 2
2004 Allegro Bus Rear Lights Not Working

Hello Everyone, I'm really hoping you can help me out. I'm at a bit of a loss. I have gone through the Freightliner helpline multiple times as well as contacting Tiffin directly and haven't found a solution yet.

2004 Tiffin Allegro Bus 40TSP with Cummins 8.9L ISL 400HP - Freightliner Chassis

History: It started out with simply just my left turn signal not wanting to flash. Then the 4 way flashers didn't want to work. This was about a month ago. I've looked at all the fuses and relays and haven't found anything not working. I ordered a whole bunch of the Tyco relays in the coach to make sure none were bad, ordered like 16 new ones and replaced them all. The other night I was going to fill up the coach with diesel for an upcoming trip when I got notified by other drivers that I had no rear lights at all. The next morning I started tearing into it and thought that I had identified voltage at the plug that the rear cap wiring harness plugs into, plugged it back together and tested it seemed to be working with turn signals, brake lights, and running lights. Went to start securing things and it went back to absolutely nothing working. Started to tear it apart again and found that there was a wire splice put on the yellow wire from the trailer hitch connector to the yellow on the rear cap wiring loom and same for the green wire. One of them was loose and not sure why they would be tied together in the first place. Some of the spots that were electrostatically welded on the tiffin rear cap wiring loom looked a little suspect but are still holding strong. The trailer hitch connector is hit or miss with the running lights working and brake lights working, the turn lights will light up both turn signals rather than just one or the other. The rear cap lights still will not work at all. The front headlights, turn signals and marker lights do work. If I unplug the rear cap wiring loom (from the Freightliner 7 pin connector) the turn signals will also blink, not just light up. If I plug in the rear cap wiring loom to the Freightliner connector then the turn signal in the front will light up but not blink. Another odd thing is that there is a Hopkins turn signal converter (usually used to get outputs for a trailer) that was there from the factory but not plugged into anything.

Any ideas on where I should start with this? The wiring upstream of the 7 pin connector from Freightliner is inside the frame rail so really hard to see if there are any issues there. The bulbs seem to be fine because one minute they will work and then the next they wont. Any help or suggestions anyone has would be greatly appreciated. I have a large 3000 mile trip coming up at the end of the month and really would like to have functioning rear lights.

I have search and found a couple of other threads but nothing that seemed to be exactly what I am dealing with here. Happy to take pictures of anything and help provide clarification where I can. Again thank you for all and any help!

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Old 07-13-2022, 11:16 AM   #2
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Tiffin Owners Club
Join Date: Sep 2013
Location: DFW, Texas
Posts: 22,389
First off, Welcome to IRV2!

I assume you checked the fuses and relays in the passenger side rear compartment? Most of your symptoms point to a loose or bad ground wire somewhere in the rear cap.
2017 Phaeton 40IH XSH Maroon Coral - Power Glide Chassis with IFS
Previous '15 Tiffin Allegro RED 38QRA and '06 Itasca Sunrise 35A
White '24 Jeep JLU Wrangler Willys
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Old 07-13-2022, 11:30 AM   #3
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Yes sir, I checked all the fuses and replaced all the relays in the rear compartment on the driver side of my chassis. I forgot to mention, at one point my rear lights would not shut off and was running down the chassis battery. The only way I could have it shut off was pulling the LT, RT, and running light relays in that compartment. That is why I thought I needed to replace all those relays.
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allegro, allegro bus, light, lights, rear

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