| 7 Prong Hitch Plug Wiring [message #268562] |
Wed, 31 December 2014 10:12  |
mickey szilagyi
Messages: 273
Registered: January 2013
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We are in the process of wiring a new 7 prong trailer hitch plug. We will use the OEM wires and circuit that run from the front of the coach for the 4 trailer light wires. These 4 wires are powered through the engine and front battery with a white ground wire. The white ground wire runs from the front of the coach but also has an additional black ground wire to the frame at the back of the coach (this additional ground runs from the OEM connector in the left rear corner of the coach).
We will run a blue wire from the front of the coach to the rear plug for future electric brakes.
We would like to run an additional/separate 12V supply to the 7 prong hitch from the house batteries that will power a dual plug addaptor like this one.
http://www.amazon.com/Reese-Towpower-74681-Power-Adapter/dp/B0016KH24U/ref=sr_1_1?s=automotive&ie=UTF8&qid=1420041235&sr=1-1&keywords= Reese+Towpower+74681+Dual+Port+12+Volt+Power+Adapter
There are 2 extra prongs on the 7 prong plug that we could use as an auxillary separate house battery 12V supply (one hot and one ground). Doing so would keep the two circuits separate with each having its own ground wire. However, the Reese dual power adaptor that plugs into the 7 prong trailer plug is pre-wired to use the same ground post that runs from the front of the coach.
Question - Can we use that same ground post (the one that is connected to the OEM ground) for both the trailer light circuit that is powered by the engine battery and the 12V circuit that would be powered by the house batteries. Basically, both the engine battery and house batteries are grounded to the body and frame so it seems like it would be OK to use the same ground wire for both. Or should we keep them separate as much as possible to prevent a ground loop.
Your suggestions/help/comments on this are greatly appreciated.
Mickey
1977 Kingsley, 403, Lansing, MI
[Updated on: Wed, 31 December 2014 10:13] Report message to a moderator |
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268565 is a reply to message #268562] |
Wed, 31 December 2014 10:22  |
sgltrac
Messages: 2797
Registered: April 2011
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The existing blue wire in the tail lamp harness can be used for the brake controller. ( ran a fresh one before I checked this place)
Todd Sullivan
Sully
77 royale
Seattle
> On Dec 31, 2014, at 8:12 AM, Mickey Szilagyi wrote:
>
> We are in the process of wiring a new 7 prong trailer hitch plug. We will use the OEM wires and circuit that run from the front of the coach for the
> 4 trailer light wires. These 4 wires are powered through the engine and front battery with a white ground wire. The white ground wire runs from the
> front of the coach but also has an additional black ground wire to the frame at the back of the coach (this additional ground runs from the OEM
> connector in the left rear corner of the coach).
>
> We will run a blue wire from the front of the coach to the rear plug for future electric brakes.
>
> We would like to run an additional but separate 12V supply to the 7 prong hitch from the house batteries that will power a dual plug addaptor like
> this one.
>
> http://www.amazon.com/Reese-Towpower-74681-Power-Adapter/dp/B0016KH24U/ref=sr_1_1?s=automotive&ie=UTF8&qid=1420041235&sr=1-1&keywords= Reese+Towpower+74681+Dual+Port+12+Volt+Power+Adapter
>
> There are 2 extra prongs on the 7 prong plug that we could use as an auxillary separate house battery 12V supply (one hot and one ground). Doing so
> would keep the two circuits separate with each having its own ground wire. However, the Reese dual power adaptor that plugs into the 7 prong trailer
> plug is pre-wired to use the same ground post that runs from the front of the coach.
>
> Question - Can we use that same ground post (the one that is connected to the OEM ground) for both the trailer light circuit that is powered by the
> engine battery and the 12V circuit that would be powered by the house batteries. Basically, both the engine battery and house batteries are grounded
> to the body and frame so it seems like it would be OK to use the same ground wire for both. Or should we keep them separate as much as possible to
> prevent a ground loop.
>
> Your suggestions/help/comments on this are greatly appreciated.
> --
> Mickey
> 1977 Kingsley, 403, Lansing, MI
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: 7 Prong Hitch Plug Wiring [message #268567 is a reply to message #268562] |
Wed, 31 December 2014 10:40 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Trying to follow your desires.
1. Are you wanting to place the automotive 12v sockets on the outside of the coach, or in the toad?
2. Are you worried about a ground loop caused by the addition of the toad 12v system to the 12v circuit?
3. You intend to run another independent 12v line to the rear, in addition to the "blue" wire?
I think, once you attach the tow bar to your coach, you will be sharing a common ground. Hard to imagine an isolated tow bar.
Electric brakes, as in independent trailer brakes? Does this mean that you will be using a trailer as the towed device, not a 4 down automobile?
With the electric brakes, you need to know the current draw and then figure out the gauge of the feed wire, based on the distance from where ever you are getting the 12v's. From the engine battery/alternator or?
I think the second independent 12v line may be redundant. Another gauge heavier, and use the same line, with proper fusing.
Tom, Ms II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268600 is a reply to message #268565] |
Wed, 31 December 2014 23:19 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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The white ground return wire currently in the system is NOT heavy enough for everything that you want to do. It is now the common ground return for the brake/turn signal, tail, and back up lights. You are now adding the brake controller and possibly and auxiliary 12 volt line.
You need to have a common ground pin in the 7 pin connector and it will be ground for anything plugged in to it. The ground pin also need to have a replacement / different larger wire instead of he one you now have. I suggest that it be #12 or possibly #10 and that it replace the existing #16 wire that you are currently using.
I have a similar plug with wiring for aux and brake on the back of my Colorado. I use a brake controller and in the accessory position I power a winch (25 amp draw)mounted on one of my trailers. One of the things I sometimes do with that aux 12v lead is provide power to charge the battery on a vehicle when I'm towing it. I have a 30 amp circuit breaker connected to that pin.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Thu, 01 January 2015 04:13] Report message to a moderator |
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268661 is a reply to message #268600] |
Thu, 01 January 2015 18:22 |
mickey szilagyi
Messages: 273
Registered: January 2013
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Thanks to everyone for your replies and comments. We don't have definitive plans as to what we might pull behind the coach. We are trying to wire the 7 prong plug to meet the demands of all the possibilities. We'd like to pull a utility trailer at times for extra storage. A towd is also a possibility in the future. We would like the plug to also provide an exterior 12V source from the house batteries.
We have a 7 wire cable that will run from the exterior 7 prong hitch plug that is 4 14 gauge wires for the trailer lights, a 12 gauge wire for the brakes that will run all the way to the front of the coach and 2 10 gauge wires for the auxillary 12V supply from the house batteries and a common ground. We plan to run the two 10 gauge wires to the interior electric closet where the positive will run from the fuse panel on either a 15 or 20 amp fuse but could be more since the wires are 10 gauge. The second 10 gauge as the ground will ground to the aluminum frame behind the electric closet.
However, we're not sure what to do with the OEM ground wires. We thought about keeping them and splicing them into the new 10 gauge ground wire back where they all come together at the back left corner inside the coach. If we did, there would still be the one white ground that runs all the way to the front of the coach that is part of the OEM trailer light wires. That same OEM ground has a black running from it to the coach body at the left interior rear of the coach. Can we keep these two OEM grounds along with the new 10 gauge ground without causing some sort of grounding issue?
Thanks again everyone.
Mickey
1977 Kingsley, 403, Lansing, MI
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268664 is a reply to message #268661] |
Thu, 01 January 2015 21:00 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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Here is the problem with running parallel ground circuits. Everything will usually work well until one of the parallel circuits opens up. Then you will have power running on unintended paths. The GMC is unique in that it has two separate 12 volt power systems and two separate ground systems that go with those power systems. Yes, there are some cross connects between those two systems (One on the trans and one on the body near the right front wheel) so they usually work OK when wire incorrectly. It is when one of those open up that problems occur.
So you need to determine what you intend to power back there off of what 12 volt system(s) and then decide which system to attach the single ground trailer plug connection to.
I'm thinking the single ground should be to the engine side ground because the engine side will be powering the tail and brake/turn signals, the trailer brakes, and probably the aux 12 volts for charging anything attached to the plug. I'm not sure why you want to attach the aux +12 volts to the house battery(s) but that is a choice you can make should you choose and if the crossover grounds connections should fail, all you would loose would be the aux +12 volts. Also you will will loosse a few 1/10 of a volt in charging voltage if you are using the aux +12 to charge batteries in what ever you are towing. The rest of the stuff in the trailer plug (tail, brake lights and brakes) would still work in the case of a crossover ground failure. As a side note: A lot of those crossover straps I have seen are in bad shape on GMCs.
I did not address the electrical noise issue when using multiple ground paths. I can address that if you want.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268667 is a reply to message #268661] |
Thu, 01 January 2015 22:30 |
Bullitthead
Messages: 1411
Registered: November 2013
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I would leave the other ground wires alone. Do not splice into either one of them. Run your new 10 gauge wire right to the engine battery ground if possible. That way all ground current will not have to pass through the body frame or the chassis to get to the battery. The engine block and starting battery ground should be considered as the master ground and all others are rooted there eventually. Make sure you use stranded wire for all of this wiring, not solid.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268680 is a reply to message #268667] |
Fri, 02 January 2015 02:43 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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Actually the engine block is considered the "Master ground" for the engine 12 volt system. If you want to shorten up the trailer connector ground wire run you could run the wire to the same location on the back of the transmission where the crossover jumper is located. It is right next to one of the transmission mounts. Running the wire to the battery just adds additional connections and length to the circuit. The engine mounted and driven alternator is the normal power source to all engine side accessories. The battery is considered an accessory that is only used during starting and as a short term limited capacity back up power supply when the engine is not running.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268685 is a reply to message #268680] |
Fri, 02 January 2015 08:30 |
mickey szilagyi
Messages: 273
Registered: January 2013
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Thanks again everyone for your help. Maybe we're trying to do too much here. We thought we could use the 7 prong hitch plug to add a convenient house battery exterior 12V source. We've taken into consideration everything all of you have said and especially what Ken has said in the past about the ground system in these coaches. We have checked and cleaned every electrical connections we could get to. We feel confident that our grounds are good. However, if we did what we propose, we could create an electrical noise issue. Ken, I know you explained this to us before, but I can't remember exactly what problems we could encounter. What sort of issues might occur? Interference with radio, computers?
We are running a 12 gauge wire to the front of the coach for future electrical brakes. Do we need a heavier ground running up there too than the OEM ground that goes up there now? Now would be the time to run it up there since we have everything apart.
Thanks again everyone, your help is great and appreciated as always.
Mickey
1977 Kingsley, 403, Lansing, MI
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268698 is a reply to message #268685] |
Fri, 02 January 2015 10:50 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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mickey szilagyi wrote on Fri, 02 January 2015 09:30Thanks again everyone for your help. Maybe we're trying to do too much here. <nope>
<snip>
We are running a 12 gauge wire to the front of the coach for future electrical brakes. Do we need a heavier ground running up there too than the OEM ground that goes up there now? <I think so, more below>
Now would be the time to run it up there since we have everything apart. <You got that right>
Thanks again everyone, your help is great and appreciated as always.
Mickey,
According to the OE diagram, the ground back there is #18. The spare blue is #14. I don't know what they were thinking....
Just an aside and a bit of left over paranoia from years of dealing with bad trailer electrics..
If you were to run an a new ground with at least #10AWG (not SAE) from the connector to someplace solid up front. You would spend some money on copper that you would never ever regret. I once had a job that involved hours of chasing down bad grounds on camping and boat (the worst) trailers.
Brakes are supposed to only draw about 3 amps per axle, so the OE #14SAE should do, but I know I would upsize it given the opportunity. You only need to by the copper once and no matter what is costs, it is still not big in the total job cost.
Notes:
Use marine grade wire. (shop the web - if you don't find, send me a note)
- It is larger than SAE by about 10%.
- It is tin plated to reduce corrosion problems.
- It is fine stranded so it is more flexible and better able to tolerate vibration.
The standard ground wire for a truck connector (SAE-J560b) is #8AWG.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268701 is a reply to message #268685] |
Fri, 02 January 2015 11:05 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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OK, Now I understand what you want the auxiliary for.
I would go ahead and wire it up as you planned, meaning Auxiliary +12 lead the house battery(s). Is should be fused or on a circuit breaker. On the ground I would run ONE ground lead to the back of the transmission. That is as good as any place on the engine block and is the closest you can get to the trailer plug without going through any extra connections.
On your questions.
Yes the ground lead needs to be sized the same or or in this case larger than any load that may travel across it. So if you are running a 12 gage for the trailer brakes, the ground return needs to be at least that large. Keep in mind that you might also be running the trailer brakes and the tail light plus brakes lights all at the same time. So I would recommend that you go with #10 wire for the ground. Since the aux lead will not normally be used when traveling, it's load will not be added to the ground return at the same time as the others previously mentioned. For the aux +12 tt will be a little longer path traveling across the jumpers and through frame and on way to the house battery(s) but it should work OK..
Oh boy, Ground loops.
Well several things happen with ground loops.
From a DC standpoint the biggest problem happens when one parallel leads in a ground loop opens for any reason and power travels across a small parallel lead instead. This usually results in burning the thinner lead do to higher current flow than what it is capable of. I like to use the example of the person who installs an extra ground wire direct from the distributor base to the engine battery negative terminal. Now there are two paths from the battery to the engine block. What happens is the main battery cable (probably #2 gage) loosens up, corrodes, etc. The current flow will now travel across the owner installed #12 or #14 gage wire through the distributor instead. Then try to start the engine using that #12 or #14 wire alternate path. What will happen is you will burn the added wire because it can not handle the starter current. That added wire on the distributor is OK (I have one) but attach the other end to the engine block, NOT the battery.
From an AC or RF standpoint you have just built yourself an antenna out of that ground loop. The antenna is resonate at some unknown frequency depending on the size of the loop. That RF or lower frequency noise will travel to anything connected to the ground system and if the devices use that frequency you have major problems. It can move fan motor or ignition noise along with higher frequency RF frequencies. In a vehicle this gets into things like radios, computers, etc. It is almost impossible to recognize and determine what is causing these items to fail (sometimes intermittently). I found one ABS computer to fail from a ground loop. I have seen it cause engine (fuel injection) computers to shut down or just random audio noise in radios etc.
I have also had to shoot these types problems in computer rooms one where an entire bank of disk drives kept failing because of an unattended ground loop. I spend about 60 hours chasing that one down over a months time of intermittent failures. The client was not happy. I kept thinking it was something in the disk drive controller or CPU to channel cables. It wasn't. It was a ground loop in the under floor cabling.
I hope I answered your questions.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] 7 Prong Hitch Plug Wiring [message #268727 is a reply to message #268701] |
Fri, 02 January 2015 18:04 |
mickey szilagyi
Messages: 273
Registered: January 2013
Karma: 0
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Matt, Ken and everyone else.
We are using tinned marine AWG wire on everything we are wiring. We will run 10 gauge on these new grounds. We appreciate your help and think we now understand what we need to do.
Thanks again for your time in helping us on this.
Mickey
1977 Kingsley, 403, Lansing, MI
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