semi truck trailer wireing

Question. Have a 8600 International semi Truck. want to have auxiliary lights (clear) on the trailer to see at night so we want to tap into the 12V in the harness but can not get a 12V power other than the lights/flashers ect.

Most wireing diagrams for the 7 pins show the "blue" wire to be auxiliary/ABS. We do not get any voltage from the blue. is the something that needs to be on to get voltage from the truck? Is our truck bad on that pin??

I think the smaller truck 7 pins have a 12V on the black but I don't think that applies to Semis.

Thanks for the feedback.

probable just not tied in on the other end-some non-rv cables aren't hooked up-or fuse/breaker isn't installed on that wire.

Blue is the aux. power, but not all trucks have it wired in, check to see if you have power at the trucks pigtail. Many trucks have the aux. wired through a switch on the dash, or a push-button breaker, for controlling features on the trailer like a tag axle, belly dump or similar. So you need to see if your truck has the switch, some Freightliners in recent years had the switch and blue wire, but did not hook power to it under the dash.

check the breakers .
about the last 20 25 years binders have use re set able breakers .
they go bad and will not hold in .

some of the newer truck need to turn key on for power thur blue wire so it works the trailer abs computer on the trailer. must newer trailers with abs have a abs light that comes on when trailer brake abs not working. if your needing a lot of power back there they make a one or two pin power cord you can install, we have them to charge battery and work the lift gates, don't forget to add a 70amp breaker when wiring it to one of your tractor batteries.

Check for a toggle switch behind the drivers seat. Not sure, but maybe.

Usually you have to have the key on the have power at the blue wire on 8600's. Honestly, it's not legal to disable the trailer ABS (and can cost you thousands in fines if caught).
What I would suggest is as follows: two of the 7 wires in your pigtail are for the marker/tail/clearance lights - the brown and the black wires. Tie these two together to the same post on the front of the trailer (at the back of the plug). Then take the interior panel behind the driver's seat loose or out to access the back of the tractor plug. Put whichever wire you're NOT using at the front of the trailer on a switch inside the cab. This makes the empty pin at the trailer on the switch - just wire the aux light back to that pin. Easy-peasy.

Spade - your local big truck mechanic

Spade has it exactly right.. Do not use the blue wire it is for the brakes..

When I did mine I hooked into the clearance and put two lights up top. I mounted a switch in the trailer up high by the roof. The lights had to be on to use them (wouldn't it be after dark anyway), and I didn't have to worry about walking away and leaving them on. You can always see clearance lights and know you left them on. When you can't see the back of the trailer from the house it is easier to leave them by accident.

Trailer is old enough it doesn't have ABS.

we had the key on (running) when we were checking.

WIll check for breakers/switches in a few days. Can't get to it right now.

No ABS on trailer (too old).

THanks.

see if there a switch marked trailer aux .

I have them on my belt trailer and grain hopper trailers both. I just hooked in to the clearance lights. I already had a junction box at the rear of the trailer so I did not have to run any long wires. Just a short run with a switch back there. Plus like some one else posted, you have the parking/clearance lights on at night anyway. This way you are not making your tractor/trailer non standard so if you pull some other trailer or some one pulls yours no issues.

My DAD thought it would be good to make his truck and trailer non-standard so no one else could pull his trailer. He borrowed my dualed tandem goose neck trailer. He was fine until it got dark and he turned on the headlight/clearance lights. His trailer used the clearance light wire for the brakes and the brake wire for his clearance lights. So he locked up the brake on the trailer going 65 mph. He put flat spots on all eight near new tires. Plus then had to figure out how to straighten the wiring out on I-90 in the dark at Chicago. He ruined $800 dollars of tires at 2000 prices. Guess who got to replace them??? You got it ME. Let alone the trailer wiring harness. He cut it at the front of the trailer and twisted the wires together to match his trailer. Taped them with duct tape. Then to make it even better he parked the trailer and never told me anything was wrong with it.

So anyway I would not wire it non standard.