Underhood Lighting

Discussion in 'SRT Hellcat Electronics' started by ChallengerDad, May 14, 2015.

  1. ChallengerDad

    ChallengerDad SRT Hellcat Moderator Staff Member Gold Supporting Member

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    I originally posted this as an LED engine bay mod, but the same principles for the lighting / wiring apply to installing an under hood light as well. You could placed LED's under the hood using 3M body-molding adhesive/tape (2 sided), or you could place a standard engine bay light there just as easily using Bellkamp fasteners, zip ties and existing holes in the under-hood bracing.
    ***This was written/done on a 2009 Challenger SRT8. CHECK for a comparable fuse location on the Hellcat before connecting your new installation to a power source. A certified Service Technician can tell you which slot to connect to safely in the fuse panel.***


    Engine Bay Lighting Mod Tutorial


    Materials

    The first thing you need to do is determine how much light you want, where you want the light to originate from, and what you want illuminated. In most applications, small light strips will work best because of their cost, weight, and intensity. I would suggest you shop around for the strips you ultimately decide to use. Base your search on price, availability, and flexibility. When I refer to flexibility, I don't mean just how much the light strip will bend or twist alone, but also on whether you can trim the strip to a shorter length without destroying it, thereby giving you less light on a particular location or part. Smaller light strips are lighter and easier to mount (require less room and adhesive) and provide a surprising amount of light when confined in the engine bay.

    [​IMG] [​IMG]

    Darker colors will absorb more light, so low light illumination will need to be more intense on those parts. HOWEVER, shiny/polished surfaces create a lot of reflectivity, which changes how the light is spread around the engine bay. The mind-numbing possibilities with OEM and aftermarket parts in our engine bays make even distribution of light nearly impossible. So you need to know that the lighting will never be completely "even" throughout the compartment. Accept that and work with it.

    Another consideration is attachment of the lights to areas/parts in the engine bay. Some will take adhesion better than others. But the biggest factor is location. We have the cowl in the rear of the engine bay to "hang" lights from, but in most engine bays, not much else exists to hang lights to shine down. No matter how evenly distributed the light may be, nothing will ruin your job faster than having lights that shine directly into the eyes of someone looking into the bay. In order to overcome this, you may have to hang lights from visible parts and point them to the sides, rear, or back of the engine compartment. While that may not be particularly difficult, hiding the wiring to keep the job "clean" will be next to impossible.

    Another consideration is "one off" parts you want to highlight. If you have something unique, you may want to cast more light on that item than those surrounding it. However, "more" isn't always "better", so use the light judiciously. Instead of adding more light on your "specialty part", consider using less light elsewhere.

    My suggestions for shining lights downward would be to hang them from the 5.7L HEMI engine cover (directing the lights over the valve covers toward the wheel wells), mounting lights from the underside of a strut tower brace, mounting lights from the underside of the 6.1L HEMI half-covers, or mounting lights on the hood and shielding them from direct view. Again, each location poses its own challenges in hiding the wiring.

    I suggest using 3M Molding Tape (part # 03614) to mount your light-strips. It holds molding to the sides of vehicles that operate in high-shear conditions successfully, and holds up well to the heat generated in the engine bay. It's double-sided, pliable, and strong, so it allows you to be creative in your light placement. This runs ~$5.00 for a 1/2" X 5' roll. Plan on using one roll for every four 9" light-strip you are mounting (you need to adhere the wiring, as well as the light itself, which takes more tape.

    After getting your lights and adhesive, you need to get wiring to supply power and the ground. In most cases, 20-gauge wire will provide ample current without posing mounting problems. You can go with single strand wire, or split wire (double strand, like speaker wire). Single is easier to work with, but you need to get twice as much and hide twice as much. I prefer single strand for ease of customizing lengths. Either way, match the color wire with the color of the engine bay so it "disappears" easily.

    The next item you'll need is an inline fuse. They can vary in design and size, but all do basically the same thing - regulate the maximum power output to your project. Only one will be required for the job.
    It would also be wise to get a small supply of the appropriate type of fuse for your in-line holder. I would suggest 10A fuses for all but the biggest jobs (ten light-strips or fewer). While the LEDs will withstand a good deal of current and heat, I prefer to stay on the lower/safe end of the scale and keep the amperage down.
    [​IMG] [​IMG]

    Next, you will need something to activate the lights. I can see the benefit of having two ways to activate your system. If you mount a toggle switch first in line, you can arm or disarm your entire system by flipping a switch.
    [​IMG]
    Then, adding a plunger-style switch second in line (near the hood seam recess) will allow the lights to go on and off with the opening and closing of the hood. Mounting these can be tricky - set it too high and you can dent or wrinkle your hood when you close it. So the best method is to start as close to "flush" as you can and go up with it from there, until it operates properly. If you're using a plunger switch like that on a refrigerator or older car door, you'll need a "normally closed" switch (which when the plunger is at rest, the lights would be "on", and when plunger is depressed, the lights would be "off").
    [​IMG]
    You'll need a tool to cut and crimp with, as well as "terminal connections" for your system. Some places sell sets if you have none of this, and are pretty cost effective. A kit with a basic electricians' tool and assortment of terminal connectors would be ideal. Now BEFORE someone jumps in here and says you shouldn't use terminal connections, but rather solder your connections, in ordinary situations, I completely agree. BUT there are times when the terminal connections are more appropriate - such as this. I used male-to-female terminal connections because I don't want to have to re-wire or rebuild the system if I need to access parts immediately surrounding the light system, and the male-to-female connections allow me to unplug parts of the system without destroying the entire harness/system. I did this on my engine half covers so I could change spark plugs or coil packs as scheduled without turning it into a major tear-down.

    [​IMG]

    I further recommend the use of shrink tube to seal off wiring connections - particularly in the rear of the engine compartment, where road spray could wet your system and cause it to short out. However, terminal connectors have short lengths of shrink tubing already installed on them and can be sealed in the same way plain shrink tubing would be used. Shrink tube could/should also be used in heat-sensitive areas where wiring could be damaged from engine heat (near the exhaust manifolds).
    [​IMG]
    Okay - on to the project.

    Build
    The first order of business is to lay out your lights. The best way to do that is "light 'em up"! Temporarily hook up your LEDs to a battery as you lay them out. Short pieces of wire with "gator clips" on each end work great for this step - simply clip one end of the gators to the power source and the other end to the LED wires. You can temporarily affix your lights to their intended location using twist-ties and masking tape. When you have them all in their intended locations, you're ready to start cutting wire. Allow yourself a "little extra" wire as you cut lengths to run between the LEDs - especially around curves, bends, and when snaking wire between parts (you can always cut a little more off, but you can't make the wire grow longer). BE CAREFUL to avoid making your wire runs near extremely hot parts of the engine, or you'll need to shield the wire with a layer of shrink tube, or insulate it another way. As you run the wire and hold it in place with twist ties, look at where you're going to "hide" the run. You need to be able to get adhesive (molding tape) in there to hold the final wiring job in place, so make sure there's a way for you to do that with fingers or tools. If not, try another location for the run.

    Once you're satisfied with your layout, have all of your lights working, laid out, and wiring between them connected, it's time to get your power and ground run to them.
    There are neater ways to do this, but I chose to run my hot wire from the "spare" fuse connector in the engine bay fuse panel (it's an empty spot with the prongs exposed - fuse location #14 ). This saves me from drilling into the fuse panel and compromising the OEM part. You can simply close the fuse panel lid on this wire without further modification when your connection is completed. DO NOT MAKE THIS CONNECTION UNTIL YOUR WIRING IS COMPLETED (or you could short out the fuse). I installed a female spade connector on one end of the inline fuse to plug into the forward prong on fuse location #14, and connected the other end of the inline fuse to my supply/hot wire. The hot wire is then connected to the male spade connector on the bottom of the shaft of my "normally closed" plunger switch, which I mounted in the opening of the radiator support where the "prop rod" would be mounted on an R/T or SE. The supply line to the lights is then run from the outer shaft (between the nut and plastic radiator support of the car) to the string of LED lights on the "power" wire.

    Along with the supply line, you need a ground line to complete the circuit to/from the lights. The ground can be made to the ground post just behind the engine bay fuse panel on the fender well. FIRST, DISCONNECT THE NEGATIVE CLAMP ON THE BATTERY IN YOUR TRUNK - TO AVOID CAUSING A SHORT AND DAMAGE TO ANY OF THE SEVERAL ON-BOARD COMPUTERS IN YOU CAR. (You can now attach your ground wire to the fuse panel post in the engine bay safely.) I've found the best connection to this post is made by stripping about 3" of shielding from the end of your ground wire, twisting the strands tightly, and wrapping the bare strands around the ground post underneath the nut and heavy copper ground connector for the fuse panel.
    You will run your ground wire to the ground wires for your lights in the same manner you connected your supply wire. Take the same pains to hide the wire run as much as possible. Again, it's a good idea to shrink tube any exposed connections after they're completed to protect them from corrosion/moisture, and prevent them from grounding out on anything they may touch in the engine bay.
    Once you have made all of the connections and hidden your wire run, reconnect the negative terminal on your battery. Now you can plug the female spade from your power supply (hot wire) to the forward prong in the #14 fuse spot in your engine bay fuse panel. If everything is connected securely and properly, your lights should light up immediately. If they do not, check the ground wire connections. If some of the lights come on, check the connections to the lights that are not lighting up and correct as necessary.
    A few pics below show some of the particulars of my installation as they should apply to yours.
    Good luck and have fun making your engine bay glow!

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  2. Snappycat

    Snappycat SRT Hellcat Moderator Staff Member

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    Well done and well written. Thanks for putting this together.
     
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  3. MrBigKid

    MrBigKid BANNED

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    Nicely done!
    I thought about doing a similar write up on my fuse block install but figured not many would be interested in all the work. Now I don't have to.
    You covered all the basics and safety points very well!
     
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  4. F6F-3

    F6F-3 SRT Hellcat Owner Hellcat Car Club Gold Supporting Member HCC Charter Member

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    You are 'da Bomb!
     
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  5. ChallengerDad

    ChallengerDad SRT Hellcat Moderator Staff Member Gold Supporting Member

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    Thanks, folks!
    Pics of the engine bay of my '09 SRT8:
    upload_2015-5-16_3-17-1.png

    upload_2015-5-16_3-13-35.png
     
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  6. Daniel Carter

    Daniel Carter Gold Member

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    This is how it looks in a Hellcat (in red, but it multishift).

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