Trailer Battery Feed Fuse

[JoshS]

I bought my Suburban used, and I've finally realized that it's not charging my trailer battery like my old Ford did.

 

I read in the owners manual that the truck should have come with a trailer brake controller harness and a "trailer battery feed fuse" which will enable the feed line in the 7-pin harness. I searched the net and found other references to this fuse, but no specifics about it.

 

My used truck came with the brake controller harness, but there was no fuse with it. Can someone tell me what size fuse this is, and exactly where it should go? It's an '04 Suburban 2500 with the 8.1L. Thanks!

[Taaaaaaahoe?]

It is a 40 amp (i think) Sqare style fuse which goes under the hood in the electrical cluster. It should point it out in the manual. Mine had a 'dummy' fuse in the place this one should go. Hopefully someone can be more exact or I can post a pic too.. (Did mine in mu 03 tahoe)

[496 XL]

I bought my Suburban used, and I've finally realized that it's not charging my trailer battery like my old Ford did.

 

I read in the owners manual that the truck should have come with a trailer brake controller harness and a "trailer battery feed fuse" which will enable the feed line in the 7-pin harness. I searched the net and found other references to this fuse, but no specifics about it.

 

My used truck came with the brake controller harness, but there was no fuse with it. Can someone tell me what size fuse this is, and exactly where it should go? It's an '04 Suburban 2500 with the 8.1L. Thanks!

 

Josh,

I have a 2005 yukon xl 2500 with the 8.1 as well,it came with the brake controller harness and wrapped with it was a 30 AMP(I believe

it was a 30 or 40 AMP fuse), this fuse is goes under the hood left side in the black plastic fuse box.This fuse box will have a blanked

with possibly a false cover over this 30 amp receptacle located at the forward right area,under this black box cover will show what location its located.If no luck locating it,just call or visit your local camper dealer or hitch dealer,once installed you should now have charging power

at the center pin on your Sub's trailer hook-up.Hope this helps,I wired up my Yukon myself and had no problems and took under an hour.

 

rgds,

Perry

[JoshS]

Thanks for the help guys. There is a dummy fuse in the engine compartment power box, it says B+. I'll try to pick up a fuse like that tomorrow and see what happens. Thanks.

 

The manual doesn't say what to do with the fuse. All it says is "This harness is for an electric brake controller and includes a trailer battery feed fuse. It should be installed by your dealer or a qualified service center."

 

Gee thanks, GM, for the help!

[az'03Silverado]

Also, under the fuse panel there are two wires. One for Stud#1 and one for Stud#2. They need to be hooked up for the brake controller to work and for the 12V feed to work. This in addition to the fuse.

[Taaaaaaahoe?]

Yes, the B+ was the one!

 

I dint have to hook anything else up besides that on my truck - and the aux power on the 7 pin was live.

[JoshS]

Okay, it works! Thanks for the pointers.

 

I went and bought a 40A fuse this morning and replaced the dummy labeled "B+" with it.

 

Note that my brake controller has always worked fine without doing this, so this fuse has nothing to do with that. The only noticeable change is that the red power line on the trailer connector is now hot.

 

BTW, the label for that fuse position is just as useless as "B+" and the wording that I quoted from the owner's manual. Nothing anywhere on the vehicle indicates that this would be the position for trailer power.

 

Anyway, thanks for the help. Hopefully this thread will help someone in the future.

[Taaaaaaahoe?]

Okay, it works! Thanks for the pointers.

 

I went and bought a 40A fuse this morning and replaced the dummy labeled "B+" with it.

 

Note that my brake controller has always worked fine without doing this, so this fuse has nothing to do with that. The only noticeable change is that the red power line on the trailer connector is now hot.

 

BTW, the label for that fuse position is just as useless as "B+" and the wording that I quoted from the owner's manual. Nothing anywhere on the vehicle indicates that this would be the position for trailer power.

 

Anyway, thanks for the help. Hopefully this thread will help someone in the future.

 

 

Correct. THis has NOTHING to do w/ the brake controller like you said it just makes that line hot. And I agree wtf is B+ to mean? When you buy the car the bundle with the trailer harness has the 40 amp fuse and a little sheet of paper with instructions explaining this. WHY its not in the actual manual is beyond me.

 

Glad you got it going!

[Jeslokin]

Excellent post guys - its still solving problems in 2009! I have the B+ plastic cap as well on a 2003 Yukon XL 2500. How do I test that a 30AMP fuse is all that is needed without the trailer (as you can see, I'm not a mechanic!)? I suspect a meter read of some sort, but I'm not sure what to do to see that a fuse fixed it.

 

Thanks for the help!

[c4cruiser]

The purpose of that fuse is to provide a 12v power source to the trailer through the trailer wiring harness.

 

Trailers with brakes on both axles have an emergency breakaway system that energizes the trailer brakes if the trailer separates from the tow vehicle. This system will have a small wire or cable leading from a connector on the trailer tongue and is attached to the truck at or near the the hitch. When this wire is pulled out of the connector, the trailer brakes are engaged.

 

Power to engage the brakes comes from a small 12v battery that is attached to the trailer. The 12v power lead on the wire harness is used to keep the breakaway battery charged up. With the 40A fuse and the large wire, you can also use the 12v source to provide power to accessories on the trailer.

[brims]

Thanks for the help guys. There is a dummy fuse in the engine compartment power box, it says B+. I'll try to pick up a fuse like that tomorrow and see what happens. Thanks.

 

The manual doesn't say what to do with the fuse. All it says is "This harness is for an electric brake controller and includes a trailer battery feed fuse. It should be installed by your dealer or a qualified service center."

 

Gee thanks, GM, for the help!

 

"This container is for window washer fluid, please consult your local dealer or qualified service center for installation of new fluid"

[sonjaab]

Stud #1 in the underhood box is the trailer fuse power! After 03 GM just had a

dummy fuse in there.

 

Note that the pin out arrangement in the trailer plug is different in the 99-02 than

the 03-07 gmt- 800s. Verify with a test light.

[Freemanj]

Great post or I would still be searching the web. My 2003 Chevrolet Suburban K1500 OEM installed Pollak 7-Way Connector just labeled the slot with a “+”, which I assume means 12 volt +. With the vehicle on, I checked the Pollack “+” lead with a light tester and that same “+” (or red wire/line) was not active. My Suburban didn’t label the “+” or “-“; however, it did indicate the other lines as:

ELECTRIC BRAKES

RH STOP/TURN

BACKUP LAMPS

LH STOP/TURN

RUNNING LAMPS

 

In the underhood fuse block in the engine compartment, I found a dummy fuse labeled as “B+” in the STUD #1 Position [usage is listed as Auxiliary Power (Single Battery and Diesels Only)/Dual Battery (TP2) Do not install fuse]. Should I replace the dummy fuse with a square 30A or 40A fuse? Why does the Owner’s Manual say to not install fuse (or is this only if you have dual batteries)?

[BubbuhWaggin]

Thanks for the help everybody! It got me in the ballpark much more than my manual or Chilton's. For my 2002 Suburban 1500 4X4 it was a huge fuse in the upper left hand corner of the under-hood fuse/distribution box. I put in a 40 Amp fuse (about $4) and all is now well for charging my RV battery. The layout diagram in the lid showed the B+ circuit mentioned but it was all "dashed out" and it wasn't clear that the circuits interconnected. There was no dummy fuse, just an empty slot. The diagram showed the fuse as being for * For diesel xxxx, or * gas 'auxiliary' or something to that effect. The pin of the towing recepticle is the #4 position and is located at about one O' Clock. Hope this helps

[intheburbs]

The one circled is the fuse for the trailer feed on the GMT800s. On my '01, the fuse was taped to the brake controller pigtail, which, IIRC, was stuffed in one of the rear cargo compartments.