2001 2500hd Dual Battery Trailer Wiring

jwick86 · June 11, 2011

I've got a 2001 silverado 8.1 with the factory dual battery setup. I bought the truck used about a year ago so I don't know if it came that way or had it put in. I did run my plow all winter off the aux battery and it charged fine.

My problem is I don't have 12v to my trailer for interior lights or the break any battery. I do have both red wires hooked up under the fuse box shield (already done when I looked) and I am not getting power to the 7 way plug. I have tried stud 1 for power with the key on and off and still no power. I did install a fuse in stud one and got power back there but I know this isn't the correct wiring as it wont be switched. I do have power to the aux isolator on both sides of the isolator with the key off, is this normal? Id like to get this wired up correctly so any help is greatly appreciated. Thank you

John

jwick86 · June 12, 2011

I just checked my options list in the glove box and I have option TP2.

All I see is a pos wire coming from the battery to the 125a fuse, to the isolator, down under the motor assuming to the starter solenoid. How would my trailer wiring get a signal from this battery?

Any help is greatly appreciated.

Thanks

John

8.1HD/ALLISON · June 12, 2011

The trailer wiring will not be switched by the key. It is a direct feed to the battery. Otherwise you would have to go turn the key on to use the lights in your trailer. As far as having power on both sides of the isolator with the key off, it should show power on both sides. One one side you have power from the stock location battery. On the other side you have power from the aux battery. You need to get a Fluke ( or digital volt and ohm meter) and check for continuity from one side to the other with key off. Should not show continuity. If you don't have a Fluke, have someone turn the key on and off for you. I would think you could hear the isolator click. Or check the signal wire for power on the isolator.

jwick86 · June 12, 2011

I did hear and feel the isolator clicking on and off. I did check with a voltmeter for power on the connector to the isolator and it shows power when the key is on and nothing when the key is off.

I have 2 red wires hooked up on the fuse box, one on each stud. Is this correct? Or should there be more? Also, where does the wire from the aux battery run to go to the fuse box for 12v? Thanks again

John

jwick86 · June 12, 2011

After some further testing and hair pulling I re tested the isolator and I've got continuity on both sides of the poisolator with the key both on and off. I've also got continuity if I pull the plug out of it, even though I can hear the isolator clicking on and off and feeling it. I have checked and there is only one wire coming off the aux battery.

Does anyone have a install sheet for the TP2? I would like to trace wires and make sure its in correct. I also would like to see how the wire on stud 1 gets its power from the aux battery to send to the trailer plug. I appreciate the help.

dewfpo · June 13, 2011

Does anyone have a install sheet for the TP2? I would like to trace wires and make sure its in correct. I also would like to see how the wire on stud 1 gets its power from the aux battery to send to the trailer plug. I appreciate the help.

There are some pics in this thread that may help.

http://www.dieselplace.com/forum/showthrea...ight=tp2+dewfpo

DEWFPO

jwick86 · June 14, 2011

Ok, I guess I'm still confused as to I am getting continuity on both sides of the isolator with the key off and in the run position. I thought I was only suppose to get it with the key in the run.

Next, where does stud 1 get its power from to send the trailer plug 12v? Sorry for being a pain I'd just like to set the truck up correctly.

Thanks for the help

John

8.1HD/ALLISON · June 14, 2011

I believe stud 1 gets its power from a fuse close to it. Should be labeled. Not sure on the continuity part, but it you can feel it click when turning key on, I would imagine it is working.

jwick86 · June 15, 2011

I believe stud 1 gets its power from a fuse close to it. Should be labeled. Not sure on the continuity part, but it you can feel it click when turning key on, I would imagine it is working.

I know with the single battery you are suppose to use a 40a fuse but I was told with the dual batteries you dont use a fuse???

8.1HD/ALLISON · June 15, 2011

I would leave the fuse in it.

jwick86 · June 16, 2011

Today trying some other idea's I unplugged my isolator and wasn't getting a reading from the alternator with it running so I have to assume its working. While the isolator was unplugged I put a fuse in stud 1 and got power out back with the truck running and off.

What is the difference in the truck wiring between a single battery causing the 12v to be switched and vs a dual battery setup on all the time? I am going crazy trying to figure this out. I want my trailer to have 12v like it should without the fuse being in as I was told not to put in. Looking for any idea's. Thanks for the help.

5Alive · March 16, 2012

Has this been resolved for you yet? What did you end up finding out?

I've installed the TP2 option, and can say that you are correct: With TP2, you remove the 40 fuse in the main fuse block, because there is a Mega Fuse holder near the auxiliary battery that fuses the output of the auxilliary battery instead.

You earlier mentioned "125 amp Megafuse". Did you assume it was 125 amps, or did you open the little box and look at the fuse value itself? It should be only 40 amps, the same value as the little box type fuse you pull from your main underhood fuse panel.

When you have TP2, then Stud 1 gets power ONLY from the auxilliary battery. This is why the 40 amp fuse is removed from the main fuse panel, because if it remains plugged in, then your main battery is involved, and that defeats the purpose of battery isolation when the key is off and engine is off.

You also mentioned "isolator". I assume you meant the continuous duty relay solenoid mounted on the firewall near the auxiliary battery. If you have a different type of "isolator" block, then perhaps the previous owner made some modifications?

The function of TP2 is to provide 40 amps of fused current to Stud 1... in lieu of the main battery providing that current. The main battery is disassociated by the removal of the 40 amp fuse on the underhood fuse panel on the driver's side of the vehicle. The fuse for the auxilliary battery is on the passenger side of the vehicle hidden behind the auxilliary battery, mounted on the auxilliary battery tray in a separate MegaFuse box.

There are several variations of wiring between this box and the starter and the solenoid. But these variations relate to how the aux battery is connected to the starter solenoid, not for purposes of helping with starting, but only for purposes of paralleling both batteries during the run (not the start) cycle of the ignition.

Hope that helps someone later, if not you now.

[email protected] · March 17, 2012

Hi 5Alive:

Good information to have - thanks for Posting it. I know NOTHING about all this - but I'd like to learn more.

So..... From the OP's Posts and your input - - - -

It seems that the Aux. Battery should feed 12v to the trailer 7 pin connector - as well as to the parking lights on the truck and trailer - when the ignition is off - and the parking light switch is on. {yes/no?}

It seems that power flows from Stud #1 with the main battery hooked up, and the original 40A fuse in place - to the 7 pin connector - on the OP's truck. {yes/no?} - but not when the original 40A fuse is pulled {yes/no?}.

To check his system:

First the OP should have checked to see that the fuse on the line from the Aux. Battery was good. {yes/no?}

Second - checked to see that there was power flowing from the Aux. Battery over to Stud #1 - with the main battery disconnected. {yes/no?}.

Or what would the proper trouble shooting process be in this case?

thanks,

Carl B.

5Alive · April 5, 2012

Hi 5Alive: Good information to have - thanks for Posting it.

You're welcome. I've installed an entire TP2 system on a GMT800 to match the OEM as built configuration exactly, wire for wire, so I just happen to be familiar with this particular set up on this particular vehicle platform.

So..... From the OP's Posts and your input - - - -

It seems that the Aux. Battery should feed 12v to the trailer 7 pin connector - as well as to the parking lights on the truck and trailer - when the ignition is off - and the parking light switch is on. {yes/no?}

Yes to the former, NO to the latter.

The TP2 auxiliary battery option does provide 12V to the trailer 7 pin connector. So the answer to that is Yes.

However, it does NOT provide power to the "parking lights on the truck and trailer when the ignition is off and the parking switch is on." So the answer to the parking light part of your question is NO.

If you leave your trailer's running lights on, the trucks main battery will be used. The trailer connector is indeed a SEVEN pin connector. The trailer's running lights (brown) and hazard/turn-signal lights (green/yellow) are still being energized by the main battery. The hot lead in the 7 pin plug is typically used to power the trailer's INTERIOR lights, exterior "work" lights, and 12V accessories. It also charges the trailer's small tongue mounted breakaway battery, and, depending on the trailer wiring, can provide charging current to the trailer's house batteries if so configured.

It seems that power flows from Stud #1 with the main battery hooked up, and the original 40A fuse in place - to the 7 pin connector - on the OP's truck. {yes/no?}

Yes.

- but not when the original 40A fuse is pulled {yes/no?}.

I forget the blow by blow details of the OP's original plight, and since the OP hasn't come back, I don't want to re-read and re-analyze his situation anymore than was already done months ago when I originally tried to help. However, YOUR question can be answered generally with another conditional Yes AND No.

IF the 40A fuse labelled as "Stud 1" in the Underhood Bussed Electrical Center (hereinafter called UBEC) is pulled,

THEN the vehicle's main battery will no longer provide power to the constant hot 12v circuit in the trailer plug. A picture of the fuse location is borrowed from another forum and linked below:

(ha... on edit, this forum won't allow an image to be shared from another forum... right. whatever. so petty. so very petty and commercial. "look at our ads, don't look at theirs" we want your traffic to show our advertisers and make money off of your contributions of time to help others out") Anyway, off of soap box, and continuing with the text only version:

IF in the case where this fuse is pulled, one would still like to have power to the constant hot 12V pin of the trailer plug,

AND,

IF there is an auxiliary battery installed exactly per the TP2 wiring configuration as originally equipped by GM,

AND,

IF there is an intact 40 amp MEGA fuse in a separate MEGAfuse holder on the passenger side Aux Battery tray,

AND,

IF there is an approx. 10 to 12 guage single red wire that crosses the cowl from that Megafuse holder over to the UBEC,

AND,

IF that red wire that crossed over the engine bay along the cowl/firewall is actually connected to Stud #1,

AND

IF there is another red wire also connected to Stud 1 that trails off toward the rear of the truck,

And,

IF there is sufficient residual voltage in the Auxiliary Battery with the engine on or off,

THEN, and only THEN,

there will be indeed be power on the constant 12v pin in the trailer plug that comes soley from the Auxiliary Battery.

The important thing above is to make sure that there are TWO wires on Stud 1, one coming FROM the Aux Battery, the other going TO the trailer plug. The metal tap on the bottom of Stud 1 that disappears under the UBEC is only hot when the 40 amp fuse is plugged into the UBEC. Otherwise, Stud 1 is dead. That's why the OP had power when he plugged the fuse in, and didn't have power when he pulled the fuse out. What the OP needed to do was make sure the wire from the Auxiliary Battery was eyeleted onto Stud 1. Then Stud 1 would be hot without the 40 amp fuse plugged into the UBEC.

Now, you can see the BIG PROBLEM if one has BOTH the red wire from the Auxiliary Battery eyeleted onto Stud 1, as well as the 40A fuse plugged into the UBEC simultaneously. The problem? Both the main battery and the Auxiliary battery just got paralleled, Not good. Defeats the purpose of the isolation coil. That's why when one poster earlier in the thread suggested keeping the 40A fuse in place, I felt that I should post something, because that is precisely what one is NOT supposed to do.

The other important thing is to know that the trailer BRAKE wire is NOT supposed to be connected to Stud 1. The power for the trailer brakes is still supposed to come from the vehicle's MAIN battery, and it attaches to Stud # 2.

To check his system:

First the OP should have checked to see that the fuse on the line from the Aux. Battery was good. {yes/no?}

Second - checked to see that there was power flowing from the Aux. Battery over to Stud #1 - with the main battery disconnected. {yes/no?}.thanks,

Carl B.

Your checks are right on, and I suspect the second check may have revealed the OP's problem. There needs to be two red wires on Stud 1 if the TP2 Auxiliary battery is in place as designed by the factory. One wire from the Aux Battery energizes Stud 1 in lieu of the main battery doing so through the UBEC. The other wire trundles off toward the rear of the truck to power one pin (not all pins, just one) of the 7 way trailer connector. It sounded to me like the OP had the wire to the 7 way connector hooked up to Stud 1, but did not have the wire FROM the Auxiliary Battery hooked up.

Note that for diesel trucks that come from the factory with two batteries, the foregoing does NOT apply. Unlike gasoline powered trucks with an auxiliary battery option, the diesel truck batteries are paralleled by intention, due to the increased compression of diesels requiring more cold cranking amps to start the motor. As such, the 40A fuse in the UBEC needs to be plugged in for diesel trucks. There is no separate 40A Megafuse holder on the passenger side. There is no battery isolation, unlike the gas trucks.

Hope that clarifies the entire dual battery, TP2, trailer wiring, and diesel difference a bit better for the long term internet record.

5Alive

[email protected] · April 7, 2012

Hi 5Alive

Thanks so much for taking the time to write such a clear and concise answer to my questions; while providing the additional information needed to gain a better understanding of the TP2 system.

I actually have my 2500HD and 20' enclosed trailer to haul a show car a few times per year - - - but living on Florida's Gulf Coast - that setup {truck/trailer} also serves as my "Hurricane Emergency Evacuation Rig" for my family. While it would not be pleasant - we could get to higher ground, park in a safer place, and live out of the trailer temporarily if necessary. So the ability to run lights and/or ventilation fans in the trailer at night, with out running the Starting Battery dead, and without having to run an external generator - would be a big plus.

Again - thanks

Carl B.