I added 55 watt back up lamps to my truck and ran them through the existing wires by tapping on and by my figures I added about 6 amps of additional load to the system. The back up lamp circuit has a 15 amp fuse and I went to 20 amps for additional protection because of the 55 watt lamps added. This should be fine shouldnt it??? All is working great.

 

Actually the fuse is there to protect the wire, not the load. By changing from a 15 amp to a 20, you are pushing the ability of the wire to carry the load past what it was designed for. Depending on how much leeway there is in wire size and total load, the wires can get hot.

The better way would be to run a new fused lead from the battery through a relay to the added lights. Wire the relay coil to the existing lights. This way the new wire takes the added load.

 

I'm no expert by any means but my understanding is that the reason they select a certain fuse is not only becuse of the intended load but also becuase of the size (or guage) of the wires. by replacing the 15amp fuse with a 20 amp fuse you are now allowing more current the posibilty of a higher current draw then the wires are rated for and out possibly cause them to heat up dangerously

But take what i say with a grain of salt. once again i am no expert.
If anyone disagrees please do so! i would love to hear more!

Cold man

 

I didnt try it with the 15 amp fuse but if it works fine should I just leave that or should I do it thru the relay as stated? Thanks guys.

 

When i get a chance tomorrow, i will look through my wiring diagrams and see what else is on that same circuit. I would not say there is much draw from everything else so you should be fine with the 15 amp. And if your not, whats the worst that could happen? you blow a fuse.

 

well by changing the fuse you going beyound whet MFG specs are for the type of wires and the lenght. fuse is just a short that when you pass throught it more current than it was made for like 15 and you drawing 16a, its going to get hot and burn, you putting 20a fuse, instead of the fuse now you might burn insulation on the wire and cause major havoc in your electrical system, so never override fuses or put bigger ones where smaller was designed.
run another wire from the battery with fuse right at the battery and then use original wire to turn on the relay, cheaper than chasing melted wires in you electrical system.

 

Actually, you added about 8A, assuming two bulbs (55x2=110, 110/13.8=7.97A). Not sure what all is on that 15A fuse, but I'd definitely want it at the original spec'ed value. My advice is that if it works with the 15A fuse, then let it go. Your backup lights aren't on all that much anyway. If it blows, run the extra length of wire with the relay (RadioShack sells some decent relays or you can probably find them cheaper you have some kind of parts whole-saler around). I'm thinking the whole thing would be Less than $25, including wire, relay, and connectors.

Joe

 

you can run your lights off of your trailer tow harness it has a seperate reverse light circuit

 

I know first hand what happens when you just add in a wire. They melt(ok can melt). Much less headache by running new wire to the batt, to a new switch, then to the lights. You do have to reach down and turn on a switch it you want more light when backing, but i think it is better than trying to figure out where smoke is coming from when you are driving down the road.

 

Yes, but in the case of back up lights, they're only on backing up, so no extra load "driving down the road"... Good advice though. Just paralleling those in there *IS* risky.

Joe

 

Ray is this harness at the rear or under the dash where you hook up a electronic brake unit?? If at the rear which wire (color code) you speaking of? Thanks.

 

I'd recommend mounting a realy back there and tapping off the trailer harness. There's a large gauge orange wire thats "hot in run" that has a 30 amp fuse, plenty for those lights. All you have to do is find out which wire on the trailer harness is for the reverse lights and have that one switch the relay on.

 

Not sure the color of the wire, but it you have a 7 pin RV connector at the rear, it is the center pin.

Here is what I did:

Used the relay with the extra wire, and used #12 wire. Overkill, but less voltage drop=brighter lights, and if you want, you can put in larger bulbs.

Then, I used a switch and a pair of diodes, wired such that either the switch or the reverse circuit can turn on the relay, and then the lights.

Now I get lights in reverse, but I can also throw the switch for light at night, to load stuff in the truck, or hook up a trailer in the dark, or other such operations.

 

Neat idea with the diodes. I think I'll do that with mine.

 

I did the diodes just to keep the switch from back-feeding the reverse circuit, as I have no idea what would happen if I did. My luck, the truck would jump into reverse or some such nonsense.