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Old 07-25-2020, 11:08 PM   #1
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THOR #19795
Smile No brake lights and no rear signal lights.

Hello All, I was ready to camp today with my 2019 thor compass 24tf. All my tailgating friends along the way alerted me to my issue with my new Thor.
I checked all fuses, checked as good as I could for wire problems, even the 7 pin female plug only had taillight power. Front signal lights work fine.
Puzzled in New Jersey, had to return home and troubleshoot to no avail.
Suggestions would be more then welcomed. The chassis is Mercedes 3500

Thank You,
Harry

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Old 07-25-2020, 11:17 PM   #2
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Originally Posted by mohican View Post
Hello All, I was ready to camp today with my 2019 thor compass 24tf. All my tailgating friends along the way alerted me to my issue with my new Thor.
I checked all fuses, checked as good as I could for wire problems, even the 7 pin female plug only had taillight power. Front signal lights work fine.
Puzzled in New Jersey, had to return home and troubleshoot to no avail.
Suggestions would be more then welcomed. The chassis is Mercedes 3500

Thank You,
Harry
Do you have a voltmeter or can you get your hands on one? I've read more than a few posts that suggested you test the fuses with a voltmeter. I personally found this to be true, especially on the tiny fuses in the chassis fuse box. Sometimes they look ok but are actually burnt. Touch each end of the meter to each end of the fuse and make sure current can flow through it. Come back if you've already done that because now you're really going to have to dig.
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Old 07-25-2020, 11:18 PM   #3
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Check your chassis manual. There may be a relay as well as fuse. Check them again.
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Old 07-25-2020, 11:38 PM   #4
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I tested fuses with Ohm meter all good. Checking thor manuals will check schematics
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Old 07-25-2020, 11:42 PM   #5
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Check the chassis manual to determine if there is a relay in the Power Distribution Center as well as a fuse. All my vehicles have relays for left and right turn as well as fuses.
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Old 07-25-2020, 11:57 PM   #6
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Check the chassis manual to determine if there is a relay in the Power Distribution Center as well as a fuse. All my vehicles have relays for left and right turn as well as fuses.
What he said. You don't cite the make of your coach. If you're mounted on the E-450 and don't have it, this might help.
Attached Files
File Type: pdf E450_Chassis_Fuse_Box.pdf (331.9 KB, 22 views)
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Old 07-26-2020, 12:21 AM   #7
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The chassis is a 2017 mercedes sprinter 3500, I'm thinking its not a fuse or relay because the front signals work. Leading me to believe its a Thor wire issue.
Thanks for your input I appreciate it
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Old 07-26-2020, 12:54 AM   #8
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Most vehicles now have separate fuses for each signal, and as Breeze says, there could be relays too.
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Old 07-26-2020, 01:37 AM   #9
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Most vehicles now have separate fuses for each signal, and as Breeze says, there could be relays too.
Relays was EA but who's counting. LOL
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Old 07-26-2020, 01:53 AM   #10
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The chassis is a 2017 mercedes sprinter 3500, I'm thinking its not a fuse or relay because the front signals work. Leading me to believe its a Thor wire issue.
Thanks for your input I appreciate it
Relays are under the driver seat tucked under the fuse panel. The Mercedes dealer swapped out the foreign ones with OEM.
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Old 07-26-2020, 02:08 AM   #11
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Originally Posted by mohican View Post
The chassis is a 2017 mercedes sprinter 3500, I'm thinking its not a fuse or relay because the front signals work. Leading me to believe its a Thor wire issue.
Thanks for your input I appreciate it

Since the front signals are working and they may just be multipled to the rears, perhaps the "rear" lighting and brake lights have a bad common ground connection?
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Old 07-26-2020, 02:14 AM   #12
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Since the front signals are working and they may just be multipled to the rears, perhaps the "rear" lighting and brake lights have a bad common ground connection?
Is bad bulbs an option and are they easier to pull? Possibly isolate a variable (the ground)?
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Old 07-26-2020, 11:27 AM   #13
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The chassis is a 2017 mercedes sprinter 3500, I'm thinking its not a fuse or relay because the front signals work. Leading me to believe its a Thor wire issue.
Thanks for your input I appreciate it
The front signals are Mercedes, the back are relays from the under the seats to the back by Thor.
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Old 07-26-2020, 12:24 PM   #14
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Is bad bulbs an option and are they easier to pull? Possibly isolate a variable (the ground)?
Bulbs are a possibly. On the Accolade the interior door courtesy lights did not work when we bought the coach. Checked fuses and all the other things then checked the bulbs. Both bulbs were bad.
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Old 07-26-2020, 12:26 PM   #15
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I would think a 2019 would be leds. Although they can burn out its less likely.
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Old 07-26-2020, 01:38 PM   #16
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Since the fronts work and the rears do not and the rears are Thor installed there could be another fuse panel with fuses or relays, the wiring could be bad our the bulbs could be bad. On either thing that is possible and that is a bad ground in the twilight wiring circuity but that falls under wiring.

That is all it can be one or a combination of the three. Breakout the multimeter and start crawling around. Since it is both sides that would indicate that the wiring needs to be checked first. If the rig is under warranty take it to the dealer and have them check it out.

Question, does your state require safety inspections and if so when was it done and who performed the inspection.
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Old 07-26-2020, 02:40 PM   #17
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On the Mercedes chassis there are THOR relays and fuses under the drivers seat that control the rear turn signals and brake lights. When mine failed it was a 15 amp fuse under the drivers seat.
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Old 07-26-2020, 10:42 PM   #18
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Thanks for all your help and advice, you guys are great! After checking fuses and wiring, it seems to be a defective control unit under the driver's seat. Mercedes part # 9069003903, the control unit receives two multiple wire plugins. I jumped a wire to from connector 1 to the right and left signal wire and rear lights came on. I plan on bringing the compass to Mercedes this week hope they don't tell me it's a Thor issue.
I'll relay the results
Harry
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Old 07-26-2020, 10:50 PM   #19
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Originally Posted by mohican View Post
Thanks for all your help and advice, you guys are great! After checking fuses and wiring, it seems to be a defective control unit under the driver's seat. Mercedes part # 9069003903, the control unit receives two multiple wire plugins. I jumped a wire to from connector 1 to the right and left signal wire and rear lights came on. I plan on bringing the compass to Mercedes this week hope they don't tell me it's a Thor issue.
I'll relay the results
Harry
Wow. Nice find. Thanks for getting back to the forum. It may help someone else someday. Update the post with keywords. You can do that in the Advanced section. It will enable the search engine to find this quicker and more accurately, enabling others down the road.
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Old 08-06-2020, 12:41 AM   #20
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Fixed

Turns out to be a software issue through Mercedes. Power to the rear lights were traced to the control unit under driver's seat. They agreed but the software had to be reinstalled. No reason given for error. Hope this helps someone else.
Regards,
Harry
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