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2019 - Waterproofing antenna installation point + routing

6392 Views 18 Replies 10 Participants Last post by  80 SUBIE
Hi all,

I'm planning on adding an antenna to my 2019 Forester for use with a Midland MXT275 GMRS/FRS radio. I'm looking at using a Diamond K515S luggage rack antenna mount for the antenna and running the cable in through an unused rear grommet behind the rear gate. That's where I could use some help.

I have a Forester 2019 Premium without the power lift gate. There's a grommet right above the left hydraulic lift piece for the gate that is used to route the electrical components for the power lift gate. Since I don't have the power lift gate, I'm going to re-use that grommet as the antenna entry point. I took off the grommet, and it allows entry into both the frame and the space behind the interior trim panels.

My questions to you all are:

1) What are your recommendations for getting the cable through that hole and waterproofing it afterward?

If I can get ahold of the original cable grommet sleeve that Subaru uses for the power lift gate, I might be able to modify and use that, but I would still need to figure out how to keep water from following traveling along the cable and into the car. If I can seal around it completely, that's the most ideal solution.

2) One the cable is in the car, what are your recommendations for cable routing?

The two options I have in mind are (1) behind the roof interior panel, dropping down one of the door columns, and then coming up under the driver seat, and; (2) dropping the cable down to below the trunk and running through spaces below carpeting up to the front.

I think I'm going to end up paying someone to run the cable for me since I don't this often and I don't want to mess up the interior panels, but.... I'm still hesitant to have someone run the cable through that roof panel area because it looks like pretty every interior panel has to be removed first before you can remove the roof interior trim panel. That's a lot of places to mess something up.

When I have the below-trunk foam insert removed, I can see some cables running towards the front. Does anyone know if there are easy cable paths that can be used without having to pull out a ton of interior panels? I've seen a few carpet cut-outs under the front seats....




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I think a urethane sealant is your best bet.
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I have used Sugru for a similar application. I used it to create a grommet when running the towing light cable through the body below the spare tire.
Thanks, I'll take a look at both Sugru and urethane sealants. I'm also looking around for the cable grommet that Subaru used for the power liftgate, since that's what was supposed to connect to that spot originally. I think I might be able to just use that with some sealant in the end around the cable to keep it all waterproof.

As for the cable routing, I did a quick experiment, and I was able to drop a pull line from that hole down into the below trunk storage space. It looks like there's some decent gaps to get cables routed towards the front from there. I'll know more once I figure out how to safely pull out the under-trunk foam on the left side to look more closely.
I'm curious why you aren't using amateur radio.
No ham license (yet). Even if I was licensed, I'd still be in the same spot with mounting an antenna and running the cable.
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Does anyone know what the part number is for the grommet harness on the right side of this picture?

That's the piece I'm trying to find, but can't seem to get anywhere.

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You could look into:
3m weatherban and 3m Window weld.
Two good sealants. Possible for your application.
This came to mind as a possibility not the exact part you were looking for but very close and should work well.

Or try a search for rubber wire grommet with boot and a few other options will show up. I'll be following this project for sure!
Alright, I finally finished my antenna install, at least as much as I'm going to do for now. It's far from perfect, but I learned a lot along the way.

For my grommet, I ended up modifying a Jandorf 1-1/2 in. Dia. Rubber Grommet from Ace Hardware.


I enlarged the hole so it could fit 1/2" split flexible tubing through it.

Next I used a hacksaw and made the groove deeper so it would fit the roughly 15/16" hole that I was putting it into. After that, I beveled the inner side so it would be easier to slip into the hole while still ensuring I have a fair amount of rubber sitting on the inside lip for waterproofing.

My decision to make a custom grommet was not one I made without trying quite a few alternatives first.
  1. Factory power lift gate grommet
    • Subaru only sells the grommet with the power lift gate kit. I wasn't going to buy a $200+ lift gate cylinder just to use the grommet.
  2. Trunk door grommet
    • I considered buying one of the grommets that connects the trunk electrical connections to the body. Subaru doesn't sell it separately.
    • Also, the hole in the body is almost 1 3/8" diameter, so the same grommet wouldn't fit in the hole I have anyway.
  3. Rigid irrigation right-angle connector (would be inserted through a hole in another grommet of sorts)
    • The idea was to angle the connection exit point down to help prevent water from getting in.
    • The antenna wouldn't fit through it without me cutting the end off and re-terminating it (something I'm not versed at and didn't want to take on)
  4. Tail light grommet
    • Exactly what I'm looking for, but not sold separately.
Trunk door grommet:

Tail light grommet:

The good news is that my custom grommet fits!

I tried using clear flexible tubing through the hole, but I was worried it would bend too much when the trunk closes and compromise the seal. The black flex tubing had a lot of challenges, notably, the inner diameter is exactly 3/8", the diameter of the antenna connection. Running the antenna connection through it was a pain. I had hopes of using the tubing all of the way down into the trunk area so I could then plug it in case water gets in, but I gave up on that pretty quickly.

Since it was split tubing, I needed to seal it, and sealing it was where I started running into problems. I tried heat shrink, but it made the tube a hair too small to fit the antenna. Initially I used several layers of electrical tape, but the pressure on the tube also made it slightly too small for the antenna. In the end, I did use electrical tape, but only a layer or two.

With the cable dropped through down into the trunk, I used a small piece of flex tubing to hold the cable in place while ensuring it can wiggle a little if it needs to:

Here's where it exits the rear pillar:

Routing the cable to the front, I tried to protect it as much as I could, but found one cable path (that made sense at the time) that ends up resulting in a pinch point once the foam panels are reinstalled:

My final solution was to run it above that metal brace and push it as far back under the plastic panel as I could. I didn't have a great spot to add another guide tube, so I used electrical tape in a few areas.

(hit picture limit, to be continued)
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To waterproof the grommet, I initially used GE clear silicone:

But after a week or two of drying, it was coming off around the tube, so I got a different kind of sealant from Home Depot. I think it was Permatex Clear RTV Silicone (can't find my tube with the leftovers). In retrospect, I should have gotten the black sealant. The clear stuff looked great initially, but eventually turned yellow :(

It's holding though!

Back inside, the cable runs through a gap along the side:

Another view of it:

In the rear seat area, this is what it looks like:

I wanted to remove the rear sill plate and run the cable under the carpeting, but it didn't cooperate. I wouldn't get the sill plate to unclip. I got it undone enough to get the cable pushed up under it and then tucked it between the sill plate and the carpeting up to the front.

It isn't really noticeable :) I used some velcro to "clip" it onto something more stationary to help prevent it from being ripped out accidently.

I used velcro to mount the radio under the driver seat, and the mic to the carpeting right next to my right leg. I sleeved a cable extender for the antenna so I can disconnect the radio easier if needed. I also sleeved the radio power connections, which go up and into the center console. I didn't take apart the center console and re-route power like others have done.



(to be continued, picture limit)
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Antenna extender connection:

Back outside, here's the antenna mount:



Since the antenna sits right next to the roof rail, I bought a cheap pack of foam crossbar protectors and used one one of them to provide some antenna bounce protection (when it's folded down).

The above picture is a bit old. Since then, I've ziptied the cross bar protector in place instead of using the cord it comes with. A small strip of velcro holds the antenna to the foam pad when I'm not using it.

Along the way, I learned a lot about some of the connections in the back seat area. Notably, the rear airbag impact sensor is mounted directly in the middle of the rear seats, on the front. For that reason, I needed to disconnect the battery while I ran the cable. Here are a few of the diagrams I was referencing (with annotations added).


When I get back into dry and warm weather, I might pull off the silicone and replace it with black silicone. For now, it's working well.
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I'm looking to install an amateur VHF/UHF transceiver in my 2020 sport; any ideas on how to route the power cable to the battery?
I didn't need to route a power connection from the back to the front for my radio, so I can't say for sure what the best route is.

If you can't plug into the accessory power outlet in the trunk area, you may be able to add a new power cable from the battery to the back following a similar cable path as the rear power accessory outlet.

I don't have the cable diagrams handy, but @Sdcerreta effectively took apart the inside of their car throughout the course of this posting. Post 76 has a good set of pictures of the trunk area with all of the interior panels removed. Post 148 has a good set of pictures of the front and side with the seats and carpeting removed (exposing the interior electrical wiring). Between those two posts, you can probably get a good idea of where it's safe to run a new cable.
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Sorry for posting in a zombie thread, but very nice work and excellent documentation. I'm doing the same thing with Skar, my 2020 Forester Sport, installing a Diamond 2 meter / 440 NMO mount antenna to the edge of the back hatch. Leased vehicle, so I have to be very stealth on the install, and be able to whip off all the accessories easily with no visible marks, cuts or holes.
I'm glad you found it useful. I wish I had found a grommet solution that didn't involve making one myself, but I never found a suitable off-the-shelf option.

Just a word of warning, if your 2020 Sport has the power lift gate option, you won't be able to use the same insertion point.
I'm looking to install an amateur VHF/UHF transceiver in my 2020 sport; any ideas on how to route the power cable to the battery?

This may help. Still haven't gotten around to installing a radio yet. I'm looking at either mounting the antenna on the roof rack or perhaps a lip mount on the liftgate. Given that I'm 67 (yikes) and a bit of a klutz, I'm considering having a professional install a suitable power cable into the under dash area to a terminal block or something like the West Mountain RIGrunner DC Outlet Panel.
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