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Just FYI for anyone wanting to wire these up, I checked out the wiring diagram for the truck backup light circuit and also the trailer hitch wiring circuit.
1)The truck backup light circuit has a 10A fuse, and stock halogens on that circuit are about 34 watts. Total capacity on that circuit is 120W. So the morimoto's are 50W, so you are at a total of 84 watts on that circuit.
2)The trailer backup lights circuit is shared with the trailer parking lights, it is a 20A circuit. If there is no trailer connected, your truck draws 0amps on this normally. 20A is about 240 watts.
So, you can use either one without the need for a relay.
I might use a relay though and have these lights turn on also if I put on the rear cargo light for loading purposes, I would have to wire that to the interior illumination circuit but believe that is 10A as well.....
Just FYI for anyone wanting to wire these up, I checked out the wiring diagram for the truck backup light circuit and also the trailer hitch wiring circuit.
1)The truck backup light circuit has a 10A fuse, and stock halogens on that circuit are about 34 watts. Total capacity on that circuit is 120W. So the morimoto's are 50W, so you are at a total of 84 watts on that circuit.
2)The trailer backup lights circuit is shared with the trailer parking lights, it is a 20A circuit. If there is no trailer connected, your truck draws 0amps on this normally. 20A is about 240 watts.
So, you can use either one without the need for a relay.
I might use a relay though and have these lights turn on also if I put on the rear cargo light for loading purposes, I would have to wire that to the interior illumination circuit but believe that is 10A as well.....
That is not how fuse ratings work. If a 10 amp fuse has 10 amps on the circuit for a certain amount of time it will operate (burn open.) If it has more than 10 amps on the circuit it will burn open faster. Every fuse has a time versus current graph that will tell you how fast the fuse will operate based on the current on the circuit. There is also a transient or surge current when you initially turn things on that needs to be considered. So basically, a 10 amp fuse is not designed to have 10 amps of current on it all of the time. You also need to consider the wire size of the tail light circuit, which is probably 16 or 18AWG. 18AWG is rated for 16 amps in chassis wiring (when it's wired in a bundle with other wires.) Bigger wire is rated for more, smaller is rated for less. That's why I said, to be on the safe side, use a relay.
However, if you know the wire size, the existing current draw, the current draw of the new lights, the fuse rating, and the fuse's time versus current graph you can determine if you'd actually NEED a relay or not.
You could also just splice into the wiring and hope for the best. Most likely it'll blow the fuse before anything bad happens; but there's also a slight possibility that it'll burn up wiring somewhere before the fuse operates and then you have to track that down.
Two low current LED lights, most likely not a problem. Two 55W halogen bulbs, that's a different story.
That is not how fuse ratings work. If a 10 amp fuse has 10 amps on the circuit for a certain amount of time it will operate (burn open.) If it has more than 10 amps on the circuit it will burn open faster. Every fuse has a time versus current graph that will tell you how fast the fuse will operate based on the current on the circuit. There is also a transient or surge current when you initially turn things on that needs to be considered. So basically, a 10 amp fuse is not designed to have 10 amps of current on it all of the time. You also need to consider the wire size of the tail light circuit, which is probably 16 or 18AWG. 18AWG is rated for 16 amps in chassis wiring (when it's wired in a bundle with other wires.) Bigger wire is rated for more, smaller is rated for less. That's why I said, to be on the safe side, use a relay.
However, if you know the wire size, the existing current draw, the current draw of the new lights, the fuse rating, and the fuse's time versus current graph you can determine if you'd actually NEED a relay or not.
You could also just splice into the wiring and hope for the best. Most likely it'll blow the fuse before anything bad happens; but there's also a slight possibility that it'll burn up wiring somewhere before the fuse operates and then you have to track that down.
Two low current LED lights, most likely not a problem. Two 55W halogen bulbs, that's a different story.
Yes like I said the taillight backup lights would have 7amp draw max (with the stock halogens reverse lights and the addition of the 50W backup lights). So your not close to 10A so there is no need for a relay or calculating the effect of the fuse at 10A because you won't get there. I don't think surge current on a little bulb would hit 3amps additional for long enough to trip that 10A fuse, if that is your point I see but I think it's not a concern since it's been done a million times with no issues.
So in my opinion, I would think a relay for this application is a waste of time and not required, and overkill.
My situation is I replaced my halogen OEM backup bulbs with 5W LED's, so I'm at 10W backup bulbs and the 50W morimoto lights, 60W total, that's 5A. No need for relay. Also no need to worry about surge current because it's all LED and I hear the inrush is almost instantaneous drop to steady.
Yes like I said the taillight backup lights would have 7amp draw max (with the stock halogens reverse lights and the addition of the 50W backup lights). So your not close to 10A so there is no need for a relay or calculating the effect of the fuse at 10A because you won't get there. I don't think surge current on a little bulb would hit 3amps additional.
So in my opinion, I would think a relay for this application is a waste of time and not required, and overkill.
My situation is I replaced my halogen OEM backup bulbs with 5W LED's, so I'm at 10W backup bulbs and the 50W morimoto lights, 60W total, that's 5A. No need for relay. Also no need to worry about surge current because it's all LED.
Not arguing that, and I actually think the reverse light circuit in my '11 is on a 15A fuse instead of a 10A.
I just don't agree with saying you have 10A, 15A, 20A, etc. available on a circuit that has a fuse with that rating.
Not arguing that, and I actually think the reverse light circuit in my '11 is on a 15A fuse instead of a 10A.
I just don't agree with saying you have 10A, 15A, 20A, etc. available on a circuit that has a fuse with that rating.
Technically true but for just trying to get things to work in my garage you can "estimate" it if you have some margin.
I used to be an engineer and be the details guy, now I'm in management and try to get things to work within budget, and let the engineers work out the details and tell me if I'm wrong. I just try to be in the feasibility ballpark.
Just FYI for the 2004-2008 trucks, we don't have that vertical bolt that was used to mount these lights as described. We have a horizontal one, and right now I'm playing with it to mount these lights, it might require the use of an angle iron bracket.
04-10-2016, 10:43 AM
