Roof grommets?


May 20, 2010
What are you all using for roof grommets for lightbar wiring?



May 16, 2010
Deer Park, WA
I concur with badge22, they are excellent but only for single cables. For multiple cables through the same hole, I use rigid nonmetallic conduit (PVC) fittings or plastic pipe fittings that are similar. Some mfg's do not make the seat area flush and they are to be avoided at all cost. When using these types of fittings, sometimes you need to grind/cut down the fittings so the lightbar can sit closer to the roof or install short lengths of pipe to fill the gap between the lightbar and the roof. In both cases, the threaded portion of the fittings is always, always cut down and deburred to keep the cable from protruding too far, pushing down on the headliner.


May 24, 2010
This is my go-to grommet:

[Broken External Image]:

I use this basic type of grommet in one of several sizes for most installs. I prefer this particular one as it uses a 3/4" hole, allowing me to use the same hole saw I use for NMO antenna mounts, and has a broad flange to seal the roof and help prevent pull-through. This grommet works for the lightbars I most commonly install, FedSig and SoundOff, as well as some Whelen bars. Do not buy cheap crap grommets, make sure they are UV resistant.

Keys to using these include ordering properly for panel (roof) thickness, 1 usually go 1/16 for tighter fit, 1/8" is good, but may not seal as well. after drilling hole, I clean debris, quick-wax roof under lightbar area, then use touch-up paint to cover the bare metal. after the paint has dried, I put the grommet in and seat it. Next, run your wires using a silicone lube or alcohol for ease of wire pass-through, especially if tight. Obviously, you can only put so much cable/wire through any particular grommet, so use the right size. Go slow, use lube, be careful not to pull the grommet through the roof due to friction. Once you've gotten the wire through to the last several inches, apply gasket seal / clear silicone to cables sparingly and seat bar, pulling last bit of cable through. Then clean top of grommet are up as needed for appearances and seal. Then, generously apply silicone sealant to interior-side of grommet to seal up roof. Let set then put headliner back in place.

While I've tried using the same product (strain relief dome nut) as shown in the above posts, I find they are too tall and/or rigid, press into the headliner, or cause too tight a bend in the cable. I like to drop the cable straight down from the lightbar exit point, and that the strain relief dome nuts don't work with lower profile bars. To be honest, I think they are just more trouble than is necessary. I have not had a single problem with any of my lightbar installs leaking into the roof where I've used a standard grommet. It could happen, sure, but so far so good. I feel like the strain relief dome nut unit would still need silicone and touch-up paint to ensure a proper seal and prevent rusting, so no benefit there. It is also a bit more complicated to install, requires a much larger hole be drilled compared to the size hole it provides for wire, and again, puts a tight bend in the wire at the headliner. In fact, if you are using a heavy, multi-conductor cable like on Whelen or older FedSig stuff, it probably won't clear the headliner at all. Cutting them is possible, but just adds more time and effort, as well as potential for error or injury, IMO.

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