Chrisreyn

Ok, I have hinted at wanting to know this in a few other threads with no answer, so maybe asking directly will help.
I want to put the truck running/tail lights on a relay and put the trailer harness running lights on a relay, so where exactly do I splice into the wiring harnes to best accomplish this?
I had thought that if I simply installed the relay into the running light wire coming from teh headlight switch, this would do it, but I am not sure if that would realy do any good.

So can someone please explain ( in small words for slow people) how to do this?

BearKiller

A relay is simply an externally switched switch.

The relay carries the big current load through the "battery" and "load" wires.

Whatever puny switch you elect to trigger the relay is somehow connected to the "switch" wire.

A "ground" wire completes the triggering switches circuit.



To answer your question, the main marker-light wire that goes to your trailer-plug-receptacle will be the "load" wire.

The "battery" wire should be fused near the HOT battery post.


Now, to make the relay turn the lights on, there are a couple of options.

Best is to have a dedicated "trailer lights" toggle switch, completely independent of any factory supplied functions.

Just run a fused hot wire through the toggle and to the "switch" wire on the relay.

The lazy man's way is to simply use the existing trucks parking light switch/circuit to trigger the relay.

I don't recommend this.

To go this route, any parking-light wire can be spliced into to provide the "switch" wire to the relay.

The rest of the relay circuit remains as already explained.


Where many miss the boat is their thinking that a relay is a magic electrical cure-all.

A relay is no more than a switch--PERIOD.

A BIG toggle-switch, properly wired with LARGE gauge wire is more positive and trouble-free than any relay set-up can ever be.

The benefit of relays is that they can route the heavy current around poorly designed wiring/switches, taking the most of the amperage away from them, so that wimpy little poorly designed circuits can be used to perform jobs they weren't designed to do.


For the parking-light relay, find the parking-light switch-wire at the headlight switch.

Cut this wire in two, leaving enough at each end to splice.

The end closest to the switch becomes your relay "switch" wire.

The end away from the switch becomes your "load" wire.

Make any sense now ??


If you need more help, holler.

Chrisreyn

THasnks BK, so its not realy feasible to use one relay for both is what I am gathering?
I m more concerned with taking the amperage load of the big trailer and all its lights off the headlight switch more than anything else..

dizzel

What bk says makes sense. and to answer you, you could use one relay for everything but that would save only your headlight switch from heavy current. Don't forget the wire that comes out of the headlight switch that you relay is still the same guage as the load wire( because you just cut it).

So the overload would just happen after the relay at the load wire itself. The result is that you get a melted power wire when you hook up to many lights.

So when BK says to put in a seperate toggle switch for the trailer lights, it's because he knows that melted wire insulator can stink alot!
Alternatively to a big toggle, you could put in a relay with two outputs (twin pole???) and run one side for the truck and the other for the trailer. This would properly icolate the trailer and truck and eliminate the need for a toggle. but you'll need to run a new wire to power the trailer parks from the relay.

I've found relays to be pretty forgiving if you initially hook them up incorectly so giver

Oh yeah LED's are a good way to drop alot of current if you want LOTS of lights.
Eric

ofcmarc

You could just use the OEM wiring to trigger the relay and run a heavy gauge 12v to the rear to supply the load side of the relay.

1 relay for truck tail lights, and 1 for trailer running/ tail lights.
You would also need 1 for each left or right turn signal (truck and trailer seperate) if you wanted them on relays.

TruckU

I'm doing the same thing, but for the trailer I'm installing the relay in the trailers wire junction box. The plan is to use the 12 volt battery line to power the relay,a dn cut the running light wire for the trigger.

RuralCruiser007

I have only had the truck for a few months, but the PO has done one good thing for me. Rather than tieing into the wiring at the back for the trailer, they have run the 7 wire trailer harness to the engine compartment. Now all I have to do is install the three relays!!!

Yes relays are a switch, but to turn on a relay you need minimal amperage compared to running the system direct. I don't remember the actual specs for turning on the relay, but if I remember right it is like 1/2 amp(Jim jump in please). The relays are rated for either 30 or 40 amps(general Bosch relays). So for decreased draw on the system using relays make a load of sense.

When, and that is a big WHEN, I will take the time(what time ) and document with pictures for this electrical upgrade.

92cummisw350le

can any one show me a wiring diagram for putting a relay in the headlights

rlyons

RuralCruiser007

I was just disecting the wiring diagram the we keep on seeing(no bad thoughts to the one who took the time to make it), but as I see it. When you look at the diagram, going off the #30 terminal from each relay, it is also tied into the headlights. With this you would always have high and low beam on, no matter if the headlight switch is on or off. It doesn't show that you are connected(red circles) and not connected(you have to look closely) , but if you are not careful then you could be sent for a headlight loop.

HTH

Chrisreyn

The wiring diagram is right.. I just installed the realys for the headlights last week following it.. there are two relays in the diagram, one for the low beam and one for teh high beam...

It sounds like the easist way to do teh running lights is gonna be to install teh relay back by teh trailer plug... I hadnt thought of putting the turn signal/Stop lamps on relays, is it realy needed? I need to find a box that will hold 5 relays then and run ALL the trailer connections( except brakes) on one I guess to do it perfect......

BK, what I am thinking now is to run a 12V source from the battery as my main,( back to teh trailer plug) and putting the relay in-line with the running light wire... that takes care of them, but then I need to install another relay in each tail-lamp wire to do them... I had hoped it would be simpler..

BearKiller

That really depends on how many brake/signal lights are on the truck/trailer.

My truck currently has ten signal lights, with two more I am planning to add; the trailer I pull most has eight;--------I need relays.

With a two-tail-light trailer, and factory truck lighting, you can get by with only using a heavy-duty signal flasher.

BUT, it would be best to relay the signals; because, you are apt to have reason to hook to a trailer, such as mine, and should be prepared.

It's kinda like keeping a loaded gun in the toilet; it is better to have it and never need it, than to need it and it not be there.

I use old gutted-out house-type circuit-breaker boxes on trailers and under/in trucks.

They are very handy for keeping several circuits in a neat arrangement and well protected.

These can be had in a variety of sizes and can be found for next to nothing at flea-markets, yard-sales, and the like.

For example: I picked up an eight pole Murray at a recent swap-meet, full of fifteen-dollar breakers, for five bucks; purchased at a home-center, it probably would have cost upwards of two-hundred bucks for what I got, so I ain't gutting this one.


Which THEM are we talking about, brake-lights or tail-lights ??


It is way easier to wire a trailer-plug completely independent of the truck wiring, with a system all it's own, than it is to try to tie it in with the existing truck system.

Find a handy spot, somewhere in/under the truck, and mount a decent sizable box to be the trailer-plug brain center; this can be under the hood, or in the bed--tucked in under a side-rail, or where-ever.


Into this box, run one BIG fused HOT wire.

Run the trailer-brake wire.

One good easy to clean/maintain GROUND wire/terminal.

A switched wire for the trailer-markers.

Find the left and right signal wires, either along the truck-frame, or at the rear, near the trucks tail-lights, and splice your brake/signal wires into them; then route these wires to the box.

In this box, you should have:

1. always HOT wire

2. GROUND

3. trailer-brake wire

4. trailer-marker wire

5. LEFT signal wire

6. RIGHT signal wire


NOW, route however many wires, that you have prongs in the plug for, into this box.

Make the appropriate connections.

In this box, it is a simple matter to add relays to the signal wires; simply mount two relays in the box, tie the relay BATTERY wires to the HOT wire, tie the trailer-plug signal wires to the relay LOAD wires, tie the truck signal wires to the relay SWITCH wires, and GROUND the relays.


Employing screw/terminal bars/strips for making all the connections makes things much neater and easier, should you ever have to add/change anything in the future.

I would go even a step farther and FUSE each trailer-plug connection, in the box, with one notch lighter fuse than is used in the SOURCE end of the wires.

This way, should something in the trailer SHORT-OUT, it will pop the lighter fuse, and you will know the problem is in the trailer, and not the truck; also, this is a BIG BENEFIT, should you plug a strange trailer to your truck and it have a bunch of wiring issues; the fuses will protect your end of things.


ALSO, by using this box, it is a simple matter to have numerous styles of trailer-plugs, all connected neatly inside the box.

AND, should you run across a trailer for which you have no plug for, you can easily rig temporary connections inside the box, without making a mess of things.


More questions, just fire away.

Chrisreyn

Wow, very informative..
Thanksor the reply. My past trailers have all been small enough that the lighting circuits were never a concern, but now we are hauling this LQ trailer, adn I am rethinking how I have it connected.
I like the idea of teh small breaker box, very ingenuis...

Jim Lane

The specifications for the coil for a Bosch #0-332-209-150 30-amp SPDT relay:

160 milliamperes current @75 ohms DC resistance.

However using my Fluke 85 III meter @12.0 VDC I was getting

150 milliamperes current @85 ohms DC resistance.

I measured 3 different relays and all were within a few milliamperes of each other.

Also I understand that Bosch Power Relay sold out and now will be Tyco as soon as the stock is gone.

So do not be afraid of the name. I was wary of them when I first saw them.

Jim

BearKiller

Is this the same TYCO of old timey toy train fame ??