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Discussion Starter · #61 ·
Anyone ever hear the terminology? (Worthless as the tits on a boar hog) that's what Nissan's customer care falls under.
 

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?? According to the schematic you sent me, BCM pin 38 must be hot as it is fed from BATT thru a 10A fuse.
Pin 51 drives the right side turn relay, while pin 52 drives the left side turn relay. Since the Left side turn relay
never turns off, we might think that the BCM has a bad output gong to that pin. Did you change it out yet?
 

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Discussion Starter · #64 ·
?? According to the schematic you sent me, BCM pin 38 must be hot as it is fed from BATT thru a 10A fuse.
Pin 51 drives the right side turn relay, while pin 52 drives the left side turn relay. Since the Left side turn relay
never turns off, we might think that the BCM has a bad output gong to that pin. Did you change it out yet?
Not yet I'm off for a week starting next Monday. I plan to get it sorted out then. Got a bcm, and another relay kit just to have spares.
 

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Discussion Starter · #67 ·
Still nada the t-one I got didn't have tape that indicates relay #3 and the 2 hookups have different color wiring. So I don't know which one is #2
 

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Don’t know if you ever got your issue solved but after stumbling upon, and reading this whole thread, only logical issue with the lit up turn signal is the BCM sending power to the left turn/brake relay when it shouldn’t be. I would expect bad BCM. Was this ever solved?

For anyone wanting more info than etrailer’s cluelessness, the 3 relays in the towing kit are for trailer running lamps, trailer reverse, and trailer Aux 12V. When they say to only plug in two of the relays for automatics and use all 3 for manuals, you can plug in all 3 on autos just fine.

The automatic outputs it’s reverse 12V via the TCM which goes to the trailer reverse wire too. The manual has a simple continuity pushbutton switch on the side of the trans like every manual ever, and they don’t want much load flowing through that so they use that to trigger a relay which is in the tow harness kit to provide the trailer backup light power. So on an auto if you plug in that 3rd relay it will just do nothing as the autos are wired to not touch that. The manuals need it or else you won’t get full functionality.

The other two relays are needed on both transmissions for full functionality. If you skip either of them, you won’t get running lights or you won’t get aux 12V depending on which relay you skip.
 

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BLtheP, (wish that was decoded :ROFLMAO: ), I was a bit disappointed that there was never follow-up from the OP. I thought that we had just about trouble-shot down to the BCM; the OP said he would replace it; then nothing :oops::oops:. All the relay discussion, while interesting, seemed quite irrelevant to the problem; at least until the BCM was eliminated. Oh well. But Thanks very much for the insight on the relay harness!
 

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BLtheP, (wish that was decoded :ROFLMAO: ), I was a bit disappointed that there was never follow-up from the OP. I thought that we had just about trouble-shot down to the BCM; the OP said he would replace it; then nothing :oops::oops:. All the relay discussion, while interesting, seemed quite irrelevant to the problem; at least until the BCM was eliminated. Oh well. But Thanks very much for the insight on the relay harness!
Lol it’s just my name.

Yeah the relay harness definitely has no bearing on this issue. I just saw the discussion/confusion about it and wanted to add info especially if somebody finds themselves troubleshooting their way down this same path later. I always wondered what the difference was between needing 2 or 3 relays, then I had an auto and traded for a manual. That swap enlightened me to the differences. Funnily enough I now hear a relay click virtually every time I hit reverse with the stick, reminding me of my findings.

Hopefully someday OP comes back and updates about the issue at hand. Really the only logical explanation is a faulty BCM triggering that relay when it’s not supposed to. The relay can’t click over without power and it can’t do that without the BCM giving it. I’ll assume that was the issue until further clarification.
 

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Discussion Starter · #72 ·
Wasn't the bcm never figured out the problem, and the dealer couldn't either. I just removed the whole kit I have normal light function now. But back to no trailer tail lights.
 

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Discussion Starter · #73 ·
I think the issue was what I posted in the #66 post. Automatic tranny's do not need all 3 relays. I plan to revisit the issue in the spring. I'm not towing anything right now.
 

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I think the issue was what I posted in the #66 post. Automatic tranny's do not need all 3 relays. I plan to revisit the issue in the spring. I'm not towing anything right now.
As I mentioned above....the third relay won't make a difference on the auto. It's unnecessary but not hurting anything. The third relay is reverse for manual transmissions. If you have an automatic, then nothing will correspond to the wiring that the third relay hooks up to, so it's basically just a dead relay plugged in behind the panel.

I don't know how you could have the issue you were having without a faulty BCM. The circuit is really quite simple and starts at the BCM. Unless a wire shorted out to another positive wire somehow, not much other explanation is possible really. Curious to see if the dealer didn't do their due diligence of diagnosing.
 

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The schematic in post #66 is from Nissan's site. It says do not use relay #3 for automatic transmission.
I know what it says. I had an auto trans truck for nearly two years and left my relay 3 plugged in despite what the instructions said. It's not a problem. Trailer tow diagram makes it pretty simple to understand too. The third relay is literally just for the backup lamp circuit, manual trans needs it and auto trans doesn't. It's not going to cause problems either way.

Take a look at the sheet I uploaded, it's pretty helpful. The trailer brake lights are combined brake/turn and they are powered by their respective relays which the BCM controls. Considering your left relay powers up immediately when you plug it in, that tells me the BCM is outputting power that it isn't supposed to. the BCM has a brain that controls these things...it has to physically decide when to activate that relay because if the brakes are being used and the turn signal is on, it has to make sure to still blink that circuit so the turn signal shows. So that tells me the BCM is acting up.

Not trying to be argumentative, but that one extra relay being plugged in really should have no bearing on this at all. You can remove it but based on the diagram and my past experience with leaving it plugged in, I think your problem lies elsewhere.
 

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But why would the trailer light function return to normal after I removed the relay kit?
I missed where you said they went back to normal. So as soon as you unplugged the relay harness the left turn/brake started working properly again? Maybe there's something funky with that aftermarket harness you used. I dunno but that makes no sense. Maybe somehow the 3rd relay was backfeeding the circuit, I don't know. They should have nothing in common at all, but if it starts behaving when you unplugged that harness, then I guess maybe there is something there causing problems after all.

I do know for a fact I had the third relay plugged in on an automatic and I did not have any issues at all. And that was on both aftermarket and factory relay harnesses.
 

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Discussion Starter · #79 ·
Yep I had all 3 on this truck for over a year. It just started after I towed that boat with the bad wiring on it. I removed the tow harness and the lights go back to normal minus running lights.
 

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Guess we’ll see what happens when you hook it back up sans that 3rd relay. That would be a super strange fix that makes no logical sense to me, but if it works…..
 
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