Wiring options for underbelly and backup lights

[GeorgiaHybrid]

Thought I would run this past the geniuses on this site. I plan on adding underbelly lights on our fiver to aid in nighttime obstacle spotting and some new, low mounted LED backup lights for eyes that are getting a little older. I have the circuits from switches on the truck dash to the trailer thru an ISO 3731 connector (yellow color with female ground). I can wire it up to just run those lights from the truck power only or use the truck power to switch two relays to light them up. If the relay method is used, I can use terminal 87 for the truck switch when hooked to the truck and use terminal 87A going thru a 12 volt switch on the trailer so when I am unplugged from the trailer, I can still switch on either set of lights.

Anybody have any thoughts as to one way or another? Or maybe a different way of doing the wiring?

[Steve from SoCal]

So you would power the relay from the truck at 87 and a switch in the trailer to 87a, I would add a diode on both power sources just for grins.    Do you really need back up lights unhooked?

 

Steve

[RandyA]

If I understand you correctly, you are using the trailer 12VDC for power to the lights?  That is the right way to do it.  Then use a low current isolated switched wire from the truck just to power the relay.  When the truck is disconnected you power the lights directly via an added switch on the trailer without energizing the relay.  Of course, the lead is properly fused. 

If you want to grin a diode can be used - but it will drop the signal voltage by .7 volts.  Not really enough to keep a relay from working but something to keep in mind.  It will keep the trailer light switch from backfeeding to the switch circuit on the truck so, yes, it is an extra precaution.

 

[Nuke-E]

If the lights have a good regulating circuit, a diode should be fine.  If they're just using a current-limiting resistor, a diode in-line will put a dent in output.

The circuit Steve described should work, though I'd probably switch it around so that the truck fed through 87a (normally closed), and the trailer switch energized the coil and fed 87. Another option would be to just have two diodes (one from each source) going into the lights.

Wait until you get here, and you'll have all the suggestions you could possibly want!

[GeorgiaHybrid]

Steve, the switch on the trailer would mainly be for the underbelly lights at night when unhooked. Those might be to be separate sets of lights, one full on bright for getting into a place at night and the other a lot less bright for "ambience" lighting while enjoying an adult beverage or two. Having the ability to turn on the backup lights is more a simple "because I can" when running the wiring.

David, I am curious about your solution though, why reverse the 87 and 87A?

[Nuke-E]

I was thinking more in terms of reliability--if the reverse lights run through 87a, the relay coil would not be energized with the reverse lights--so if you lost either of those connections (coil power or ground), or the coil failed, the reverse lights would still work.

[rdickinson]

I put 8 under the trailer and 6 under the truck. 

Power for trailer lites comes from trailer batteries thru  a relay. 

Lites come on thru a reverse switch, dash switch or switch in battery compartment for night lighting when disconnected

18 watt lites are adequate .  You can only lite up so much road from that angle.

Also leave them on at nite, inverted takes care if batteries. 

Surface run wire down frame rails on top of tin underbelly. 

[RandyA]

I don't have any underbelly lights on the trailer.  But, after seeing Roger's the wheels in my head have been turning.  Bright LED outdoor floods or spots are much less expensive than a few years ago.  While backing into a site after dark is rare for me they would also be handy for night repairs or finding a lost item - two things that do/have happened.  Anyway, I have several RF remotes made for car door or trunk locks, garage doors or small winches.  IMHO wiring a receiver into the trailer with the necessary relay and power supply circuits would eliminate running any wires in the truck, adding yet another connector between the truck and camper or adding another switch.  A simple remote would ultimately cost less than the wire, switch, connector, etc. in the truck.  The remote for a winch has a relay inside eliminating the need for an external relay/socket.  Harbor Freight has one here.  Just an example, not an endorsement.  Normal cost is $39.95, use a common 20% off coupon and not only get it for $31.95 but with the right coupon pick up a free and very handy VOM in the process.  Need a coupon?  I'll scan one and email it to you.

[MrSeas]

I used On of these......

https://www.amazon.com/gp/aw/d/B01CCSG2ZY/ref=mp_s_a_1_5?ie=UTF8&qid=1492569130&sr=8-5&pi=AC_SX236_SY340_QL65&keywords=433+remote+control&dpPl=1&dpID=415MyF-3%2BvL&ref=plSrch

 I used the system to control my trailer under belly LED floods (aka Roger), a reverse flood LED at the rear of the trailer, RGB LED string lights, and lights to illuminate the leveling jacks.   So far it works pretty good. I just keep on Fob in the trailer and the other fob in the truck. 

[rdickinson]

It is 210 am and Im up.

I will turn on underbody lites, take some pics and send to Randy.  He can post for me.

High power is not  the answer nor needed. You are not liting up the back 40, just immediately adjacent to the rig.

Still need to be mindful if what us above. 

When going into a location at note, I walk it first and drop reflective road markers on desired path for trailer.

[rdickinson]

Pics sent to Randy.

He is not a morning person so not sure when they will get posted.

I found 2 critical areas when backing or parking at nite. 

One is knowing where the back of the trailer is.

Rear of trailer is 14ft from pivot point.

Truck fairings and bottom of underbody.

Sometimes you have to back up a grade to a pad and jackknife into the spot.

The transition from backing up the hill to transitioning to semi level pad can be a high spot which can damage truck.

I have lites in those locations plus a cameras on passengers side mirror looking down that side.

I try to take the stupid out of things. 

Even then, if it needs me to get out of the truck X10 to check, I do.

I NEVER let people help me back up.

I tell them no thanks. 

Some are offended. ..This isn't my first rodeo.