Interior trailer lights not working

Wallrat · 01-01-2007, 10:30 PM

My trailer has 2 dome lights that haven't worked since I got the Titan. Never really bothered me much but the Mrs. has been giving me grief about fixing it. So I've been doing some searching and am now totally stumped.

I've got the big tow, but checked to make sure relays #1 & #2 are there. I not only checked the 2 fuses above the accelerator, but EVERY fuse in the box behind the battery - everything is good. I'm using a voltmeter on the constant 12v of the 7-pin (upper right pin) and the 7-pin ground (lower left pin) and I ain't getting a damn thing. My ground is good cuz I'm getting a nice reading when I turn on the lights and hook the + up to the running light pin (upper left). I'm trying to remember when I hooked up my brake controller if there was an extra wire in there - I seem to recall that there was. Is there something you gotta do w/ the wire harness for the constant 12v?

Any other ideas?

TitanosaurusRex · 01-06-2007, 03:52 PM

The way my trailer was wired my dome lights are fed from the running light circuit.
I have some trailer wiring issues, I know, because every now & then the brake light fuse blows.
T Rex

**loufish** · 01-06-2007, 05:09 PM

Have you tried with the ign key on? I think the titans 12v feed on the tow harness is only hot with key on...

Wallrat · 01-06-2007, 05:14 PM

Yep, key on, engine running/not makes no difference. All other lights, including running lights, work fine.

Learjet · 01-06-2007, 09:01 PM

make sure the tow relay is actually installed.

Wallrat · 01-07-2007, 04:39 AM

Its there all right, and I removed/re-installed em to make sure I had good contact.

bestatchess · 01-07-2007, 04:55 AM

I think the #2 relay in the front left corner of the box controls the constant +12V. Make sure it is present, propertly seated, and working.

There are fuses in the both the relay box and in the other box under the hood. I would double check all of those with a DMM for continuity.

There was a TSB where a BCM sub harness with fuses was installed in some vehicles under the driver's side dash. I think you can find that TSB at www.nissanhelp.com I think it was for 2005, although I don't think it pertained to the constant +12V.

If all of the fuses & the TT 2 relay is good, my next attempt would be to investigate the harness & electrical connector for the hitch. My thought is that there needs to be continuity between the +12V pin of the electrical connector at the back of the truck and one of the contacts of the TT 2 relay socket. To make sure I didn't short anything, I would disconnect the negative battery terminal. Then I would set my DMM to check continuity, connect one probe to the +12V pin at the back of the truck (obviously you probably need a long wire to do this) and then I would pull the TT 2 relay and probe the relay socket contacts with the other probe. If you don't have continuity between one of the relay socket contacts and the +12V pin, it seems to me that the harness must be open somewhere between the relay and the +12V pin.

bestatchess · 01-07-2007, 05:07 AM

Here is the thing about the BCM sub-harness:

http://www.nissanhelp.com/Ownership/.../NTB05-086.htm

There are apparently fuses in that sub harness for trailer lights, but I don't think for the constant +12V.

Helinut1970 · 01-07-2007, 07:43 AM

You will need to have a constant hot installed to the plug. Mine did not work either until I ran a constant hot. one of the wires in your trailer pigtail will go to the lights so you will need to match that up in the truck hookup.

bestatchess · 01-07-2007, 08:05 AM

My 2004 Big Tow 7 pin connector has a pin that reads +14.6 Volts with the ignition on. He is saying that his does not have that. Something is wrong with the wiring or fusing in the truck.

Matching the trailer wiring to the truck wiring could also be a separate problem, but if he doesn't have a pin on the connector at the back of the truck that goes hot with the ignition, something is f'd up.

Helinut1970 · 01-07-2007, 08:13 AM

Yes, if hes got BT then something is not right. I dont have BT so I had to do it myself.

bestatchess · 01-07-2007, 08:19 AM

If you don't have BT, if you install the hitch & the 7 pin connector, and add both relays (I think it is 3 relays for 2006), you will be just like BT. For 2004 & 2005, the relay that you install in the front left of the relay box controls the constant +12V.

bestatchess · 01-07-2007, 08:24 AM

Is it possible that you guys are using an aftermarket 7 pin connector that is not compatible with Nissan's pre-wired harness?

See instruction for installing Nissan 7 pin here:

http://www.courtesyparts.com/instruc...5-A6000_6.html

Wallrat · 01-07-2007, 02:54 PM

I do have the BT and didn't do any wiring other than the brake controller. Anybody know what I need to test on relay #2? I've got a DMM so I'm gonna go yank it right now and see what I can find out.

Ok so I was down there pulling relays when I realized that it wouldn't be a relay that was causing this. I figure that the pin in question should have 12v regardless of key position, light switch, etc. So therefore its gonna be a direct (fused) run from the batt to the pin. Anyone know what fuse it is? I pulled em all but maybe one of the contacts got screwed up when the fuse was put back in. I dunno. Still could be the wiring between the fuse box and the trailer plug too.

Learjet · 01-07-2007, 07:51 PM

The 12 volt thru the 7 way connector is thru a relay, the tow relay. Also, the key must be on to supply pwr.

Not sure what you meant by your last post.