Pruis Gen 4 Wiring Question

 

This is a bit off-topic, but since it relates to travel, I thought I would post to see if I can get an answer.

Does anyone know how to run a power cable from the passenger compartment to the 12V battery on a Gen 4 Prius?

I am not a car aficionado, but Gen 4 is the current version which first appeared in I think Model Year 2016. Previous models had the battery in the trunk/hatchback area, which makes it fairly easy to access the battery. In the Gen 4, the 12V battery is in the engine compartment. I can't seem to find much info online to route a power cable through the firewall.

Thanks.

How much power?

beagle.fan wrote:

Does anyone know how to run a power cable from the passenger compartment to the 12V battery on a Gen 4 Prius?

I am not a car aficionado, but Gen 4 is the current version which first appeared in I think Model Year 2016. Previous models had the battery in the trunk/hatchback area, which makes it fairly easy to access the battery. In the Gen 4, the 12V battery is in the engine compartment. I can't seem to find much info online to route a power cable through the firewall.

Thanks.

How much power? For something like an extra gps circuit, I'd piggy back off one of the auxiliary outlets in the console. There are also things called something like Add-a-circuit that let you add a separate fused circuit to the interior fuse panel to power some significant things without adding any load at all to an existing circuit. Those things plug into an existing fuse slot and give you two fuse slots powered by the main interior bus supply.

I ran a 4 gauge wire to the '09 Prius battery in the trunk for my aftermarket audio amp, and even without the firewall, that wasn't a trivial routing exercise.

I looked at my wife's '16 Prius. There's a lot of empty volume between the back of the valve cover and the fire wall, but no way to get your hand in there to reach the firewall. There are 2 fuse boxes in the engine compartment, one on each side, so there's almost certainly a wiring harness penetration through the firewall on each side. It looks like the one on the passenger side goes through a little lower -- almost right behind the glove box. The driver's side one looks like it goes just under the windshield mount. Of course, getting enough of the dash out so you can reach anything high on the firewall is another interesting challenge (probably). I've had the '09 dash apart several times, but haven't gone after anything behind the dash on the '16.

--
Dave - Garmin model 45, III+, V deluxe, SP2610, Nuvi 760, 1450, 2797

I

think this is a common question for dash cams where the lighter socket is always on--people usually want the power to switch off when the car is off, so if plugged into the lighter socket (if they are even called that today who smokes in a car), they would keep recording.

The common answer appears to be to run a wire from a kit to the fuse block, where the wire looks like a fuse/blade on the end, so it plugs in.

I have a Lexus LS and it has a place for such on the passenger side. That's not the main fuse area, it's like a secondary. maybe it's the same because all a Lexus LS is, is an overgrown Camry, which is a Toyota. Off the top of my head there's a forum called Prius chat because I went to it to see what color the coolant is on Toyota products (it's pink starting in 2004 and red prior). Maybe you can get a specific answer there...

More Info

Based on the responses, it looks like I should have been a bit more specific.

This is for an amateur radio transceiver. I need to run a fused, 30-ish amp power cord between the engine compartment (12V battery) and passenger compartment. However, that is FAR easier said than actually done.

Prius firewall

The Prius is a highly technical car. Aside from a 12 volt battery it also has a 350 volt battery. A short would wreck havoc that might be expensive to repair or even total the car. In the past, it was usual to disconnect the 12 volt battery before doing electrical work, but this has bad implications for today's cars with dozens of computers that could be affected. We will not be disconnecting the 350 volt battery as this is a job for Toyota Service.

Disclaimer - I have no specific knowledge about the Toyota Prius.

For any car, it would be best to view both sides of the firewall to avoid interference with existing wires or other equipment. A location high inside the engine compartment may be inaccessible under the dash. A location visible under the dash could be too low in the engine compartment to access. Consider using an inspection mirror, a two-inch or so mirror on a stick.

Dbreiser brought up the glove compartment. Many glove compartments today are designed to be completely removable to access equipment such as the HVAC filter located behind it high under the dash. The glove compartment could have several wires attached that might be difficult to unplug, but it could be done.

To choose a location, follow one or more wiring harnesses that already go through the firewall. Consider locations near existing fuse boxes. The wiring harness could have a large rubber grommet at the firewall. After viewing both sides, consider where to cut through and pierce the rubber without damaging the harness itself. Use a knife or an awl. Avoid using a drill. Use an electrician's fishtape or a wire hanger to push your wire through. It may help to have two people, one for each side, to make sure nothing is damaged.

The 12 volt battery may have a solid-state current sensor on either the (+) or (-) side. Connect your fuse and wire on the battery side of the current sensor without putting any force on the sensor. Your fuse is absolutely necessary.

dobs108 smile

Re: Glovebox

I am sure it is easy once you know how to do it, but What's the "secret" to removing the glove box?

prius videos

Here is a video that shows how how easy it is to remove the lower glove box and air filter in an older version of the Prius, but the newer versions are the same.

There is a terminal block and wiring harness to the right of the filter housing. This terminal block has many small gauge wires which would need protection from work in that area.

https://www.youtube.com/watch?v=M3KBG0NABjM

Here is a video that shows how to remove the upper glove box. This is more difficult and it may not give you a view of the firewall.

https://www.youtube.com/watch?v=foQ2FXLiAdw

Here is another idea on the driver's side of the car:

https://priuschat.com/threads/power-through-the-firewall-gen...

Check this...

The applications explained are both relatively high amperage much like your need. One suggestion is about wiring a transceiver.

https://priuschat.com/threads/power-through-the-firewall-gen...

--
John from PA

Basic Safety Configuration

dobs108 wrote:

We will not be disconnecting the 350 volt battery as this is a job for Toyota Service.

The good news is that assuming the car is functioning properly, and that you don't have it turned on, the traction battery (aka HV battery) is already disconnected from everything else in the car.

This is an important safety feature. For example it makes it far less likely that emergency services people trying to extract a wounded passenger from a wrecked car will accidentally tie into the high voltage.

It is actually the most strenuous job left to the 12V battery in a Prius to activate this connection when you turn on the car. Momentarily it wants something like 50A. That is way less than spinning the starter motor in a conventional car, but way more than the string of electronic controllers which make up most of the standard 12V load.

--
personal GPS user since 1992

Ham Radio Connection

beagle.fan wrote:

Based on the responses, it looks like I should have been a bit more specific.

This is for an amateur radio transceiver. I need to run a fused, 30-ish amp power cord between the engine compartment (12V battery) and passenger compartment. However, that is FAR easier said than actually done.

I thought that a search with "prius" and "Bob Bruninga, WB4APR" would suffice but I got too many hits for my available time. Perhaps that'll help.

n4lbl

Ham Radio Connection

beagle.fan wrote:

Based on the responses, it looks like I should have been a bit more specific.

This is for an amateur radio transceiver. I need to run a fused, 30-ish amp power cord between the engine compartment (12V battery) and passenger compartment. However, that is FAR easier said than actually done.

I thought that a search with "prius" and "Bob Bruninga, WB4APR" would suffice but I got too many hits for my available time. Perhaps that'll help.

n4lbl

Gen 4

John from PA wrote:

The applications explained are both relatively high amperage much like your need. One suggestion is about wiring a transceiver.

https://priuschat.com/threads/power-through-the-firewall-gen-4.171436/

Yeah... I think I saw this post at some point. No pictures nor video explanation to go with it, though.