Running wire through firewall for trailer lights

vt_miata

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2016 CX-5 GT / 2006 MX-5 Miata GT
Like many others on this forum, I have a need to tow with the Mazda5. I put the hitch on ( relatively easy, remember those safety glasses ) but the wiring is a problem. I have a Curt wiring package that wants to run a wire from the rear ( inside ) up and into the engine compartment to connect to the positive battery terminal. After crawling around on both sides of the front, I cannot find a cheater location to run the wire through the firewall to get to the battery. I had an evil thought to run a feed from the rear power terminal to get the power but the instructions say that will be a bad idea. Has anyone done this and, if so, where did you go through the firewall to get to the battery? Thanks!
 
the easiest way to run the wire through the firewall is on the passenger side. There is plenty of space there. There are also some pre-cut plugs that could be removed easily and could be used for extra wiring.

Dima
 
Don't bother with the battery. Pick up the hot wire from the cigarette lighter by the back door. Don't bother to run the wires through the body. Just store them under the tool tray and close the rear hatch on them when you tow. I'll send you a picture if you like.
 
so if I wanted to wire a rear fog, I could tap into the cigarette socket?

I'd like the rear fog to only operate with lights so I should tap into the head light harness ya?

<this is sorta on topic right? trailer wiring -- rear fog wiring>

m.
 
Don't bother with the battery. Pick up the hot wire from the cigarette lighter by the back door. Don't bother to run the wires through the body. Just store them under the tool tray and close the rear hatch on them when you tow. I'll send you a picture if you like.

I looked at doing this, I did this on my previous van. I just stowed the wires in the compartment on the left. My concern was the fact that they used a 12ga wire to connect to the positive terminal and the wiring from the rear power outlet is considerably smaller. They even mention to not plug directly into a fuse but how much current can 6 lights draw anyway?

I even thought of getting a cigarette lighter adapter and only plugging in the harness when I tow.
 
I looked at doing this, I did this on my previous van. I just stowed the wires in the compartment on the left. My concern was the fact that they used a 12ga wire to connect to the positive terminal and the wiring from the rear power outlet is considerably smaller. They even mention to not plug directly into a fuse but how much current can 6 lights draw anyway?

I even thought of getting a cigarette lighter adapter and only plugging in the harness when I tow.

Mine works fine with the power coming from the power outlet. Remember that it is "switched" power so the trailer lights will not work if the ignition switch is off. Shouldn't be an issue in real life.

The other thing to remember is that the insulation on the thin tail light wires is very tough. The crimp "t" connectors will likely not cut it, figuratively or literally. I had to score the wires with a knife and then line up the connector so that it was on the score when I clamped it down.

If I had to do it again I would take it to a trailer shop or a stereo shop and have them do it. I'm guessing they would charge 1/2 hour labor but it would be right the first time.

Good luck!
 
why not use the tail lights wiring?

For some reason, all of the 'hardwire' setups want to tap not only into the tail lights but also into the battery. I've had other setups that had no such requirement, go figure.
 
There is just enough "juice" to drive the taillights. If you tap for a trailer, there will not be enough power. That is why you have the box that taps into the hot wire from the battery.
 
For the record, I ended up drilling a small hole ( ew ) and using a grommet/silicon to allow the wire through the firewall on the passenger's side. That was the toughest part. Routing the wire through the car was easy ( most trim pieces just popped off ) and the lights checked out on the trailer. Thanks for the all the advice.
 
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