Toyota Tundra Discussion Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
40 Posts
Discussion Starter #1
I'm having a hair-pulling issue where all the running lights on both my trailers work, but signals/brake lights do not. Checked all fuses, and I'm getting voltage at the appropriate pins on the Tundra's 7-pin connector. However, when checking, I've discovered I've got 12v (engine off) on the running lights pin, but only 9.5-10v on both brake/signal pins. I've also discovered the signals/brake lights on the trailers will do a single dim flash when the running lights are off, then do nothing. Ground connection is good. I'm wondering if anyone's had this issue, and I'm starting to think the only possible problem spot could be the flasher relay (bad or oxidized contacts within the trailer side of the relay - can't find a pinout/schematic to check my theory). Don't want to drop $75 for a new flasher relay if I'm missing something else to try first. Thanks in advance!

edit: should probably mention I've got factory tow pkg
 

·
Registered
Joined
·
13,643 Posts
Have you tried the plug with a trailer light tester? Only inquiring as we (my work) sold trailers for many years, and about 30% of the time the issue was with the trailer, even when brand new. Even if it wasn't the trailer, it was much easier to diagnose if it were a truck or trailer issue with a tester, plugs right in. Quite often if it were the trailer issue it was due to wiring rubbed through, causing light issues.
 

·
Registered
Joined
·
40 Posts
Discussion Starter #3
I'll have to go pick up a tester. Used my meter and got voltage on the terminals when signal and brake applied, though a few volts less than the running lights which makes me wonder if it's a bad relay and not making a solid contact to carry the current for the trailer signal lights.
 

·
Registered
Joined
·
40 Posts
Discussion Starter #4
No dice with the tester, the lights don't come on for turn/brake pins. Brake controller, running lights, and +12v works. Tried again with the meter and getting 12v on the working circuits and 9-10v on the signal/flasher pins. All connections and fuses are good, so I'm at a loss for what else it might be other than the relay.

Both trailers worked fine last week, now both have no signal/brake lights (brakes work). Forgot to mention in the first post, I tried a 12v power source on the trailer and confirmed all lights work, so I think it's safe to eliminate any error on the trailer side.
 

·
Registered
Joined
·
13,643 Posts
What year truck? I see Canada, you might possibly be fighting corrosion somewhere. I am not sure if the trailer plug has a plug in connector up stream to the harness. I have seen that issue on a lot of trucks here in MI.
 

·
Registered
Joined
·
40 Posts
Discussion Starter #6
2011... I already did a quick check, nothing I could find, though I'll probably do a more thorough check tonight.
 

·
Registered
Joined
·
40 Posts
Discussion Starter #7
Did a full trace from the bumper to the fusebox - nothing wrong, all contacts in the connectors were factory fresh (kudos to a solid connector design that hasn't changed over the decades!). Did some more trial and error, and found that when I press the brake and check with the meter on the turn signal pins, I get 10v, but then if I put the 7-pin tester on, no lights; removed the tester and pins now show 0v. WTF?! I pulled the 2 brake relays in the engine fuse box, terminals all good - reinstalled. Now all working. I'm going to chalk it up to a little chunk of carbon on the inside of the relay contact that prevented any usable current to the 7-pin.

Thanks everyone for your suggestions!

Side note: there is 0 stock in Canada for the flasher relay and costs $156 CDN - service guy says he's never replaced a flasher relay in any Toyota. Definitely hit up the wreckers for one if needed since they seem to be a pretty indestructable design.
 
1 - 7 of 7 Posts
Top