OK electrical guys heres one 4 ya!

[MxerChris]

put a set of 55 watt driving lights on the rear of the truck under the bumper for night trailer hook up etc. , wired it to a switch at the dash (power supplied straight from battery) and also tapped into the back up lights wiring at the rear of truck. Here is the strange thing with the truck off and key out, and shifter in reverse (5spd), turn the switch for the lights on and the fan blower and my CB come on, take it out of reverse and the fan and CB go off (switch still on for lights) Whats up with that???

 

[Hohn]

Your wiring is jacked up (duh). Don't you think this question is almost impossible to answer with telling us how you installed your CB and more on how you installed the lights?



What switch to do connect to on the battery? Did you install another switch? Where did you ground it? Where's your relay wired (ground and hot)?



When this happens, is this with the CB and blower ON?



If you tapped power downstream of the blower for your install, then your switch could turn an "on" blower off, but NOT an "off" blower on. Same for the CB.



Details, man. If you want help, you have to give us the info we need to help you.



HOHN

 

[MxerChris]

CB is wired in under dash to a hot with key on wire (don't know what wire it is) there is no relay for the lights, theres a (1) hot wire straight from battery to the rocker switch, (2) ground wire from switch grounded under dash to metal framework, (3) switched supply hot wire to the lights. The lights are also wired (tapped into) the back up lights at the rear of truck. The blower and CB have to be on to be affected. The thing that I thought was odd is the shifter has to be in reverse for this to all happen, when you move it into neutral the blower and CB go off. I understand that somehow the switch being wired straight to the battery is supplying power regardless if the key is out, and sending that power into the wire that I tapped into at the rear of the truck for the factory back up lights, what I don't understand is the link between that wire and the blower?

 

[Hohn]

The reason it's affected by the shifter is because of the little switch that turns on your stock backup lights when you put it in reverse.



Shame on you for tapping a hot wire that you don't know what it is!!



First of all, you need to wire your lights off a relay. Even smaller ones draw too much juice, and will make your switch hot. That can cause an electrical fire in your cab. You should ground your lights back by the lights, on the frame somewhere (rear bumper mount maybe?)



I would take all the wiring you did out and start over.



Sorry.





HOHN

 

[MxerChris]

I did ground the lights at the bumper, the short ground wire at the switch is for the illumination light in the switch itself, and I will leave the wiring I have and run additional heavier wire for the relay, I know there is a reverse switch for the lights but that still doesn't explain why the blower comes on when its in reverse.

 

[Hohn]

you have married the two circuits. when you shift into reverse, the backup light switch takes over because it is wired downstream of the main switch.



You probably should at least install an accessory block to make these things easier to sort out.



Hohn

 

[Big White Beast]

sounds like your back feeding...........

Too lazy to break out the manual but it sounds like the blower is powered from the same point as the reverse lights. This is obviously where you drew power for the CB also. When the truck is in reverse you complete the circuit. Where you had current flowing one way in normal operation it's now backfeeding. There are probably other things on this circuit also you just haven't noticed yet.



Hohn is correct, run the lamps through a relay. You will have to use diodes to stop the same thing from happening when you power the relay. Run a heavy wire straight to the rear and switch it with the relay, fuse protect this wire to be on the safe side.



If you need a diagram I can draw one up and fax it to you.



Garrett

 

[jkern]

FUSES, FUSES, FUSES...

you are definetly backfeeding thru the reverse switch to get the CB and the blower on. here is the way it should be wired... for simplicity and safety sake. tap the battery with about a #8 gauge wire, don't go more than a few inches until you fuse it with about a 30amp in-line fuse (#8 will handle 30amps ok) then run that wire in the cab under the dash and break it off into a couple #12's or #14 wires and then fuse them lighter (20 amps for the #12 and 15 amps for the 14). after that run these wires to the hot side of the relay contacts, then on the switched side of the relay run #12 wire to the rear of the truck, a single 55 watt light draws 6-7amps so you wnat the wire to be big enough to A) handle the load without voltage drop and B) handle enough current (amps) to blow the fuse instead of getting hot and starting a fire should you ever have a short in the wireing. only use the switch in the cab to control the coil side of the relay, some #18 or #20 wire is good enough for that fused at about 5 amps. or you can get power for you switch to pass along to the coil of the relay from a KNOWN key switched source inside the cab. NOW... as for the CB run it off of the other circuit that (#14) we made. it should be fuse inline from the factroy at about 5 amps or so. i know this sounds like a lot of work, but it would be a very nice professional installation that lends itself readly to adding on to in the future for other accessories. plus the fact that everything is fused so your risk of fire is greatly diminished. don't think for one second that an install without fuses is ok and that a fire won't happen to you, because with all the sharp metal edges and a moving vehicle especially on rough road, etc, those wires will chaff quickly and problems will occur. i am sorry that this it so long, but really it is the only way to properly wire accessories.

 

[THerman]

Put a diode on the tap from the back-up lights. This will prevent backfeeding the other accessories through this circuit.



The others have it right, you are powering these other accessories through you b/u switch on the shifter.



The diode will prevent this.



Tod

 

[Big White Beast]

Tod......

You are correct in that the diode will prevent backfeed. Only problem is the current draw from these lights will destroy most diodes. They aren't rated for that kind of duty. That and I don't believe the stock back-up light circuit will handle it, as this whole thread has shown there are many other things on that same power circuit. That and the wiring is probably way under-rated.



Jkerns Idea is the right way. As an option Geno's sells the painless wiring kit. You could save half the money making your own but it's so much easier to just install it and start wiring.



Garrett

 

[THerman]

Agreed. I overlooked that there wasn't a relay in this circuit.



I would have to also chime in and say that the relay is definately needed. The Jenos painless wiring system is excellent... and well worth the money. I would still isolate the reverse system with a diode... . but in just the control side of the relay, the current requirement would drop from 10A to 1Amp... . these are very available.



Thanks Garrett... . I missed that fact!



Tod

 

[jkern]

diode = voltage drop...

if i remember right from education many years back, putting a diode in the circuit will always net you a 0. 6 volt drop across the diode, not to mention the size that it would have to be to handle 20 amps. i am not saying it is wrong to use one, just thinking out loud about the issues that it may present.



-jkern

 

[Big White Beast]

Voltage drop may be the wrong way to look at it........

It takes . 6V to bias it. Meaning it needs at least this much to open up and let current flow.



You are right about the size to handle 20 A. The relay is the way to go.



When I refered to a diode earlier it was in reference to activating the relay with the reverse light circuit. Most relays draw miliamps for their coil. This would stop back feeding up the reverse circuit when you used the switch. You could diode the switch wire that feeds the relay also. If the switch is off though it wont feed anyway.



The typical automotive relays that the auto parts sell will handle 30A across their contacts so you should be fine in that respect. The only thing I have found so far, and this is for a different application, was that a relay with a low impedance coil will let a circuit see ground through it. This messed with the PCM on the OD off circuit. But that's another story.



Garrett

 

[Tim1]

back feed

Hey garret, what are you referring to as back feed from the control wire that activates the relay? It is the sigal wire which will turn on the trucks back up lites and the rerlay contacts will turn on the high load lights, right? Reason that I ask, is that I used two 40amp potter blummfield relays to power my low and high beams on my first gen truck. I didn't think that the signal wire would be any kind of a problem rerquiring a diode. Thanks Tim

 

[Big White Beast]

Tim1

Racing fan was talking about powering the lights from 2 seperate sources. The existing wire to the reverse lights and a switch in the cab. The power from the switch in the cab is what is backfeeding up the existing reverse light circuit. A diode will block that.



Garrett

 

[David_VT]

Relay works, and consider this..

Hi,

Since I don't often tow with my truck I decided to wire up my backups via the trailer plug. When I do tow I just pull the plug and it rests on top of the reciever.



I bought a plug and wired/used the trailer feed (+) switched by the reverse feed (+). The ground was also brought from the plug. A short pigtail runs from the plug up to near the spare where I mounted the relay and pulled the switched side feed to the 55w aux backup lights mounted high in the outboard sides of the reciever. That mounting location has proved to be the most reliable for my harsh winter roads. I destroyed/corroded 2 sets of backup lights mounted in the reciever or hanging on the bumper.



I have no manual control of the lights but never intended to do that . I guess I could just splice into the trucks backup switch if I ever want to add that.



In my horrid corrosive environment I've never had problems with this setup. The trailer plug is kept well greased and that is it.

==

As a foot note, this summer I intend to relay isolate the trailer (+) supply and the feeds to all my Vol emergency lights so that I can eliminate any chance of parasitic drain when the truck is shut down. I had a 12V plug in my bed , routed from the battery that corroded and did numbers on my batteries last winter. I fear that the trailer feed has the potential of doing the same thing.