Aux. Lights, relay needed?

[Harley Anderson]

I am not the best at electrical items but I added some reverse lights to my truck for when backing up to trailers at night. I do not like to splice into the factory wiring so I wired two 55 watt flood lights to a switch and a inline fuse at the battery. The lights only last a couple of months and the bulbs burn out. Should I add a relay and will that fix my problem?

 

[WishIhadatruck]

It is possible that if you used too small of wiring you would have a voltage drop in the lines and that will cause an increase in the current flow which might burn the bulbs out faster. Assuming the switch is rated for the current needed to power 2 55 watt lights and the wiring is big enough the relay won't help. With the back up lights on check the voltage at the light and see how good it is. It should be similar to the voltage at the battery. If you have a significant voltage drop run a larger wire back and use the existing wire to operate a relay near the back of the vehicle. It is farher to the back of the vehicle than to the front so larger wiring might be needed than typically used for these lights at the front of the vehicle since the length of the wire will be longer. what size did you use? The other possibility is they are not that high of quality lights. Make sure they are well grounded as well.

 

[Curious Kid]

with each bulb drawing about 4-5 amps (watts = Volts x amps), that totals about 8-10 amps for which you would want your wire of large enough gauge to handle, for whose length will also effect the gauge due to its resistance. That said, switches need be of higher amperage capacity, and the fuse being something like 1.5 the load amperage for which is in the safe capacity for the wire.

I'm not sure as to why the bulbs are not lasting long - perhaps the filament design can't take the vibration, is a halogen bulb that is running dim perhaps due to voltage drop across through the lines (bulbs run at lower temperature and the process of filament metal recycling is effected), and/or has been handled directly with fingers or is being contaminated by the elements (water/muck infiltration), leading to hot spots which causes thermal stress upon the glass IIRC leading to breakage.

I don't think a relay is necessary as some of the inexpensive light kits some without them and use something like 14-16 gauge wire and a 10 amp inline fuse IIRC. I however use the wire for switching a low current signal to a 20 amp automotive relay that switches power that's tapped off the battery's post terminal or power buss. The higher power lead is fused as close to the power supply voltage as possible to minimize risk, and all electrical usage for the low and high current in that circuit is drawn after that fuse. Automotive circuit breakers are also available in a range of current ratings (manual and auto reset), and can be used in-place of the fuse.

Take care, and sorry if this doesn't come across very clear - in a hurry to get ready for work.

 

[Chris142]

If you do put a relay in


http://www.6066gmcguy.org/BoschRelay.htm

 

[Harley Anderson]

Thanks for all the info. I am out of town for the weekend but went and checked the truck. I am running 14 guage from the lights to the battery and a 30 amp inline fuse. I am going to drop the fuse down to a 10 amp and measure the voltage drop from the battery to the lights as suggested. The lights are cheap 4" tractor lights from tractor supply. I going to add a relay also just to see if that helps them live. Doing things yourself can be more of a pain in the butt than buying a pre-packaged kit but helps you learn through problems. I have a randy ellis light bar on the front with 4 6" hella lights (2 pencil and 2 flood) which had everything in the kit including a relay and 2 switches which caused me to suggest running a relay to keep the voltage constant.

 

[Harley Anderson]

One last ?, where in the wiring should the relay be placed? I am assuming in line with the power wire to lights, but do I place it as close as the battery as possible?

The link that Chris left showed a great diagram, thanks for all the help.

 

[WishIhadatruck]

I don't think it really matters where the relay is. Where ever convenient. I've been rethinking what I wrote before and I think I might have been thinking wrong about the amount of current being affected by the voltage drop. The relay and larger wire might help with the proper operation of the lights but actually might not affect the current since the voltage across the battery shouldn't change. I should re-read my electrical book, it has been too many years since I've had to think about it.

If the voltage drop at the lights is too low then go with larger wire and a relay but I would definitely lower the fuse to at least a 15 amp to protect the current wiring if you don't upgrade. Could the lights be getting too much vibration where they are? That will affect their life as well. Try a different brand bulb also. Quality does vary.

 

[another Todd]

Relays are the bomb. Install one and your switches last forever. Install it properly and your lights and other electrical divices will have all the electricity they need. Using switches to switch heavy electrical loads will just cause headaches later.

 

[Dyoel182]

Originally Posted By: another Todd
Relays are the bomb. Install one and your switches last forever. Install it properly and your lights and other electrical divices will have all the electricity they need.


Seconded. I use one on my low beams and on my fog lights.