2020 GMC Sierra 1500 as a Toad

[wlf00]

I just purchased a 2020 GMC Sierra 1500 Denali and plan to install a Blue Ox baseplate and an Air Force One braking system myself. Has anyone done this installation themselves? Are there any things to look out for? Any helpful hints you can share?

The coach is a 2012 Winnebago Tour on a Freightliner chassis.

[GCSuper]

I'll give you a friendly bump to the top as I just ordered a 2020 Silverado and plan to use the same set up.

[wlf00]

Originally Posted by GCSuper

I'll give you a friendly bump to the top as I just ordered a 2020 Silverado and plan to use the same set up.

Thanks GCSuper. I just received the Air Force One and the Base Plate in the mail today.

The one issue I have is that GM states that the negative side of the battery should be disconnected when flat towing. But the Air Force One requires a connection to the battery. How are people doing this? Are you using a battery disconnect switch on the positive side of the battery? Is there a need to have a 12V battery charge line coming from the coach?

[PeteDr]

I have checked back several times to see if you are getting direct help, and since it is slow in coming, decided to offer at least some info that maybe indirectly helpful. I am using a 2018 sierra CC, 4WD, short bed, SLE with Elevation package. The coach is a 2019 Newmar Ventana LE. So not an exact match, but some of my experiences may be good thinking points to verify.

You need a Sierra 4WD option that has a "4WD Low" and a "Neutral" position. Starting in the 2019 model year Sierra offered a basic "4WD" without the "4WD Low". These are not flat towable. It may be a standard item on your model, but it was a $350 upgrade on the 2019 SLE/Elevation.

Your Sierra has a Multiplex wiring system the uses Pulse Width Modulation and distributed Nodes for 12 volt functions. As a sheep skin holding electrical engineer since the dark ages I thought I could integrate the DC and PWM and make it work. WRONG, came close but there was at least one function that did not cooperate. In the end I wired the Sierra such that it had two separate electrical system, one powered by the Sierra battery and a second powered by the coach system. Sounds more complex that it is, just takes a couple of blocking diodes and the Roadmaster latching battery disconnect in the Sierra.

I have a "Stay in Play Duo" braking system which sounds like it has the same negative battery cable removal problem with feedback of the entire chassis ground system back through the brake controller. The solution in the previous paragraph take care of the problem, also.

And a final big one. Electric power steering. You have it as I do. You can not disable it other than removing the positive battery lead, as the unit wants to steer straight even when the tires want to turn when in toad mode, scuffing your front tires at best, breaking the power system drive unit at worst. Again the positive battery disconnect approach will solve this problem.

Those are my thoughts as to what I believe are areas you should investigate to assure they are not going to be problematic for you and your vehicles.

[wlf00]

Originally Posted by PeteDr

I have checked back several times to see if you are getting direct help, and since it is slow in coming, decided to offer at least some info that maybe indirectly helpful. I am using a 2018 sierra CC, 4WD, short bed, SLE with Elevation package. The coach is a 2019 Newmar Ventana LE. So not an exact match, but some of my experiences may be good thinking points to verify.

You need a Sierra 4WD option that has a "4WD Low" and a "Neutral" position. Starting in the 2019 model year Sierra offered a basic "4WD" without the "4WD Low". These are not flat towable. It may be a standard item on your model, but it was a $350 upgrade on the 2019 SLE/Elevation.

Your Sierra has a Multiplex wiring system the uses Pulse Width Modulation and distributed Nodes for 12 volt functions. As a sheep skin holding electrical engineer since the dark ages I thought I could integrate the DC and PWM and make it work. WRONG, came close but there was at least one function that did not cooperate. In the end I wired the Sierra such that it had two separate electrical system, one powered by the Sierra battery and a second powered by the coach system. Sounds more complex that it is, just takes a couple of blocking diodes and the Roadmaster latching battery disconnect in the Sierra.

I have a "Stay in Play Duo" braking system which sounds like it has the same negative battery cable removal problem with feedback of the entire chassis ground system back through the brake controller. The solution in the previous paragraph take care of the problem, also.

And a final big one. Electric power steering. You have it as I do. You can not disable it other than removing the positive battery lead, as the unit wants to steer straight even when the tires want to turn when in toad mode, scuffing your front tires at best, breaking the power system drive unit at worst. Again the positive battery disconnect approach will solve this problem.

Those are my thoughts as to what I believe are areas you should investigate to assure they are not going to be problematic for you and your vehicles.

Thanks PeteDr for your comments. The Sierra SLT and Denali 4WD both come with the two speed transfer case with a neutral as standard. So I am OK there.

The GMC manual states that the negative side of the battery should be disconnected in order to flat tow. I am assuming that if I disconnect the positive side instead, it will do the same thing. I had also read that the electric steering could be a problem if you do not.

You mentioned that the Sierra uses PWM and a multiplexed electrical system. If I use blocking diodes on the tail lamp assemblies, can I use the light signals coming from the coach for tail and brake lights. These signals are 12V DC and not PWM based.

I would assume that if I use a disconnect on the positive side of the battery, I can run the charge line from the coach to the battery side of the disconnect. And I would also tie the Air Force One Braking System to the battery side of the disconnect as well.

Do you have any information on the disconnect that you used? How did you hook it up? Is there some fail safe method to make sure that the battery is always disconnected so as to not damage the steering system if one forgets?

Thank you all for any help.

[PeteDr]

Lets go from the bottom up on your subjects:

The Demco latching solenoid is a Roadmaster 766 Remote Battery Disconnect. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 where I obtained mine. It has a very good diagram on the wiring that I use. As for being sure the 12 volts is disconnected to the electric steering, it will be totally obvious, as when you activate the disconnect, everything goes dead just like you removed the battery. I have made one rule for my hookup procedure so the two electric systems never see each other. Rule is activate the toad battery disconnect first then plug the toad cable into the coach. Reverse to disconnect the toad, pull the coach end of the cable first.

On your charge cable and Air Force One this is the same as I did.

Agree, the PWM stops at the node that handles the rear lights and the connection to the actual lights is DC. Somehow, if you really try like me you can creates feedback and confuse the node. But to your question, yes I also brought the trailer hitch light wires to one side of a dual blocking diode with the other input the toad light wire. Only one input wire has voltage at any one time and all is stable.

The problem with the steering does not exist until you add a brake controller. The brake controller, at least on my Duo controller, needs 12 volts power and as such needs a negative battery connection. When you disconnect the negative battery cable, the path for all chassis grounds is back through the brake controller and the electric steering is active. Actually this configuration is dangerous since everything will try to work through the small gauge wire.
GM just does not address a brake controller in their Owner Manual.

And you are ready to go on the 4WD.

Sounds like you are ready to get to work, and it is a decent size job. Good Luck.

[wlf00]

Originally Posted by PeteDr

The problem with the steering does not exist until you add a brake controller. The brake controller, at least on my Duo controller, needs 12 volts power and as such needs a negative battery connection. When you disconnect the negative battery cable, the path for all chassis grounds is back through the brake controller and the electric steering is active. Actually this configuration is dangerous since everything will try to work through the small gauge wire.
GM just does not address a brake controller in their Owner Manual.

I am a little confused with this statement. What I was planning on doing is use the battery disconnect on the positive side of the battery and leave the negative side of the battery connected to the frame. Is this what you did? Then there is no need to disconnect the negative side of the battery.

I plan on hooking the charge line from the RV and the positive lead for the Air Force One Braking System to the battery side of the disconnect. So when the disconnect is open, power is only supplied to the braking system.

I think it would also be good to place a power diode going from the charge line from the coach to the toad battery. This will prevent the toad battery from back feeding anything in the coach. Your comments?

Thanks,

[PeteDr]

wlf00, let me try to be clearer. Without a brake controller, when you disconnect the negative battery cable nothing is connected to the battery negative. Then, you add a brake controller, it is mounted on something connected to the frame, metal to metal contact and the controller then has another wire connected to the negative battery post. So the negative battery post is connected to the brake controller by a small gauge wire, which is connected to the frame with the controller mounting screws, and the frame now has a return path to the battery. The positive wire on the electric steer can not be disconnected so you have a positive at the electric steer and a negative through the frame back to the battery via the brake controller negative wire to the battery. It is working again.

Paragraph 1 and 2 I agree and this is what I did. On paragraph 3 my initial reaction is I would not do this. The diode will have somewhere around a half volt forward voltage drop. Big deal on a 12 volt battery charge level. I also can not think of a situation when in tow configuration where the voltage in the toad battery would be higher than the coach. I did put a 20 amp fuse in the charge line just as a safety net for the unexpected.

Hope this helps

Edit: Just to be clear the above is the situation when you disconnect the negative battery cable and install a grounded brake controller. Disconnecting the positive battery and only the positive cable solves all of the above, less the charge line which is a separate subject.

[wlf00]

I would just like to say thank you to all who responded to this thread.

I just finished installing the Demco Air Force One Braking system on the truck. I still have to do the RV side yet. I also installed the Roadmaster 766 Automatic Battery Disconnect and the Roadmaster 156-25 Towed Vehicle Charge Line Kit. Both were purchased from RVupgrades.

For anyone who is interested in doing this to their vehicle, etrailer.com has videos on installing all 3 of the above mentioned products on a 2020 GMC Sierra.

I will mention that I am going to install an LED indicating light on the dash of the RV to indicate that the toad brakes are being applied. The Demco Technical Support Team indicated that if you want to run the signal up to the RV, a relay should be incorporated to drive the signal rather than just the reed switch itself. So that is what I did.

[Dabigsnake]

I spoke w Airforce one tech today, and they said the pos has to be removed from the truck when using a controller and breakaway switch. W neg disconnected from battery, there is still a ground fed to frame as you explained, as well as through the hitch from RV. Do you have experience with either disconnect on these setups? Thanks

[wlf00]

Originally Posted by Dabigsnake

I spoke w Airforce one tech today, and they said the pos has to be removed from the truck when using a controller and breakaway switch. W neg disconnected from battery, there is still a ground fed to frame as you explained, as well as through the hitch from RV. Do you have experience with either disconnect on these setups? Thanks

The Roadmaster 766 Automatic Battery Disconnect that I referenced above disconnects the positive side of the battery via a solenoid and a switch mounted on the dash.

[bsheet2]

Thanks for all this info! I just purchased a 2021 Sierra 1500 to use in flat tow mode. This thread is a big help!

One question though. Does the battery disconnect switch solenoid fail open or fail closed?? I am timid to depend on that solenoid switch to keep the the battery positive disconnected. If the solenoid fails it could connect the battery. The GMC owners manual states that the parking brake could activate when you are flat towing if the battery is not disconnected.

I am wondering if a manual switch might be a safer option.

Anyone know how that switch works??

[Aangulo1]

Originally Posted by bsheet2

Thanks for all this info! I just purchased a 2021 Sierra 1500 to use in flat tow mode. This thread is a big help!

One question though. Does the battery disconnect switch solenoid fail open or fail closed?? I am timid to depend on that solenoid switch to keep the the battery positive disconnected. If the solenoid fails it could connect the battery. The GMC owners manual states that the parking brake could activate when you are flat towing if the battery is not disconnected.

I am wondering if a manual switch might be a safer option.

Anyone know how that switch works??

I just installed a 523198-5 Road Master EZ-5 Base Plate Kit and a manual positive battery disconnect right next to battery on my new 2021 GMC Sierra 1500 Duramax Elevation edition. Job was done by Monty at M&G Engineering in Athens, TX. He also wired a positive directly from coach to cabin so a 12 volt cig lighter receptacle can be installed to connect the RVi3 brake system.

[Dabigsnake]

I went w a manual disconnect to pos cable. I have the only thing left connected to battery is my AF one brake controller n break-away disconnect. I’ll try to attach pics