(Finished) Wire Routing - A Pillar Trim and Speaker Cover Question

[Moby]

I need to run a wire from the rear view mirror down the driver side A Pillar and down into the footwell. Easy to get across the headliner gap at the top of the window.

I found several threads but nothing specifically addressed the problems I'm having in detail:

1. I may not need to remove the trim just to tuck the wire in but if I do is it easier to get the wire down through the mess of stuff under the dash?
2. How does the A Pillar trim come off? I'm nervous about just hacking in with the air bag in there.
3. Does the driver side speaker cover on top of the dash just pop off with trim tools? Wondering if this might be a route to get the wire down through the dash.

TIA!

 

[Moby]

Continued search terms turned this up: How to remove headliner? - https://forum.ih8mud.com/threads/how-to-remove-headliner.1236779/#post-13567614

This probably gives me enough to go on from routing the wire, except for the avoiding the airbag trigger question. Is this just don't screw with the wiring for it or is there a physical way to accidentally trigger it?

 

[CharlieS]

The a pillar trim on my land cruiser came off with some tugging after removing the two grab handle bolts and the handle itself. I removed the sun shades and the upper grab handle to more easily access the space above the headliner. I did this to run the switchpros control head wire to the sunglass holder. No idea about the speaker, I've never removed them. I did pop off the panel on the end of the dash to see what was going on under there better (it is just held with trim clips).

 

[grinchy]

remove the grab handle and bolts
trim pops off
route the wire along the windshield down to the tweeter area, then loop under the airbag and along the dash.
pull the pinch bulb at the door and the trim down the side of the dash, including the sill plate and probably the black plastic horizontal piece the TPMS reset button and OBDII connector is in.

run your wire where you want it and put it back together.

 

[CharlieS]

Also, I always disconnect the grounds to my batteries (I have two) for 15 minutes-ish before messing around with anything near airbags or airbag sensors. No sense in tempting fate.

 

[tbisaacs]

Are you wiring a dashcam? There are solutions that involve tapping mirror power instead of running through headliner and pillar.

 

[Moby]

No I'm wiring a radar detector with a remote display. It will be powered via the driver side fuse box with the remote on the dash.

 

[Moby]

Just to tie this off, everything worked out as described above. I did pull the negative battery cable to be safe.

For anyone else looking, the pnl1 5amp fuse is a good tap for illuminating switches (or pnl2). The wiper 30amp fuse for ignition hot. See next post for fuse block pic.

V1 cable zip tied to the stock harness:

Side panel off to route it to the kick panel:

 

[Moby]

And... new light bar, frenched into the HE grill (cut out a section). The switch (next pic) is wired from the high beam fuse in the engine bay so that you can only turn the light bar on with the high beams, and turning the high beams off automatically turns off the light bar.

Switches, AirOnBoard blue is a perfect match for stock:

Driver side fuse panel taps. Between the orange pieces you can just see the tail of the tap for the panel light. The main tap in the right corner of the panel is the 30 amp wiper ignition hot that drives the relay.

The orange pieces are Deutsch Jiffy Splices. I standardized on Deutsch solid contact terminals/connectors a while back and use them everywhere. DMC AF8 crimper. Even if water isn't a problem it's nice to not worry about dust. The switches have Deutsch connectors as well.

Good ground on the fuse block mounting bolt. All ring and quick connect terminals (on the relay above) are Tyco PIDG (crimps the wire and the insulation in one crimp - bomber):

 

[CharlieS]

I don't remember which way is right for those add-a-fuses. If they are in backward, there isn't any fuse protection.

You probably have this right already, but I messed it up at one point, and had to flip my add a fuse around to correct it.

For some reason, I thought the switched positive bus on the wiper switch fuse is in toward the center? I honestly don't remember though.

 

[Moby]

I don't remember which way is right for those add-a-fuses. If they are in backward, there isn't any fuse protection.

You probably have this right already, but I messed it up at one point, and had to flip my add a fuse around to correct it.

For some reason, I thought the switched positive bus on the wiper switch fuse is in toward the center? I honestly don't remember though.

Ah, thank you, I will double check this when I get back to my house with my main shop. I knew I should have stuck my multimeter in the truck. I'll pull them until I can confirm and report back here so we have a record. They are just accessories, I don't need them regularly (the light bar is on a separate relay under the hood, the tap here is just to illuminate the aux switches with the stock switches).

Actually now that I think about it you may have posted up the orientation. I think I stumbled across this before. I'll go search.

 

[Moby]

Found the post that I was thinking of. I have to make a run to Ace Hardware so I'll see if they have a cheapee multimeter to confirm.

 

[Moby]

OK, $19 multimeter later, it isn't consistent row to row. Or perhaps it is. The "hot" side is the side towards the center row for the outside rows, at least for the fuses in question (didn't check the center). In the picture above the panel1 fuse tap is "correct" (aux lead coming off the non hot side) but the wiper fuse tap is wrong. Flipped it around.

Thanks @CharlieS !

 

[Moby]

I would love additional input on the following... and thanks again to CharlieS for making me think about this. Never can be too safe with electrical.

I went to double check my high beam fuse tap and found it was "wrong" as well. This really got me thinking (read: quite worried). So I did some testing and some internet "research". There isn't a wrong way to install these that leaves the additional circuit unprotected because simply put the link is on the opposite side of the fuse to the pig tail wire. But the behavior is definitely different based on installed direction. Here is what appears to be going on from what I can tell and why the additional circuit is always protected...

What happens is that when the pig tail is on the same side as the input + if the lower fuse blows the additional circuit will just stop working. I tested this by pulling the lower fuse (additional circuit stops working) and by pulling the additional circuit fuse and checking which side the input + was on. It is opposite of the pig tail wire even when the tap is installed incorrectly.

When installed correctly both circuits are independent. The lower can blow and the additional circuit will keep functioning. In series versus in parallel.

There are multiple videos of people doing more involved testing to prove this than I did. I simply wanted to double check and then come up with a circuit diagram for the tap itself that matched my observations. If it was simple, I would believe what I observed.

(bad) drawing. + is the side from the battery. Hot when the fuse is pulled. Hi is the high beam load side. The dashes are the stock fuse block terminals. The boxes are the fuse terminals in the tap. Squiggles are the fuses. Pig Tail is the aux wire coming off of the tap. The line between the top and bottom boxes is the link that flows current to the upper fuse and pig tail wire. Note that the two are just reserved pictures of each other. "Wrong" has the link between upper and lower after the lower fuse. If that lower fuse blows no current gets to the upper fuse. "Right" has the link before both fuses. Either can blow without impacting the other. See below for why I actually prefer "wrong".

Another argument that there is a "wrong" way is that the load of the additional circuit runs through the lower fuse. But regardless of the direction of the tap it puts the same load on the stock wiring, so I'd rather protect the stock wiring with all of the load through the lower fuse and just have the upper (additional circuit) fuse protect the additional circuit's wiring. That way the stock wiring is always protected by the stock size fuse no matter how much load the additional circuit adds (never bump up the lower fuse!).

 

[CharlieS]

I think it is even simpler than that - one side is always hot, one side is protected by fuses.

edit: I was wrong so deleted the bad information. See @Moby post below for the right answer.

 

[Moby]

Just in case - I'm not trying to be argumentative



Start at min 3. He shows what I'm describing above, and how the current has to flow through the lower fuse to reach the upper when installed wrong.

At 5:40 he shows what happens with a tap installed backwards and a fuse in the top only. No power to the pig tail wire.

The current is flowing across the fuses regardless of orientation. The only difference is how the current gets to the upper fuse. But current is definitely not flowing straight up, bypassing the fuse, when installed wrong.

He disagrees with installing it wrong because it will overload the stock fuse. But if you are overloading the fuse you are overloading the wiring as well. 8 amps through 18ga isn't safe whether you are using 1 fuse or 2. I really want that bottom fuse to carry both loads so that the stock wiring is always protected.

 

[CharlieS]

I don't know.

I eventually used a multimeter and found the side that was hot (12v+) when the ignition was on, and put the add-a-fuse output wire on the opposite side.

My thinking was that if the output wire was on the same side as the 12v+, the fuse wouldn't be in line between the power source and the equipment (load), so the fuse wouldn't be doing its job of protecting the wiring during a short. (edit: This is wrong, it actually puts two fuses in line between the source and added load.)

I could be completely wrong. (edit: I was wrong)

(Edit: Yep, I was wrong. I watched the full video you posted, and I agree that what he says is the right way to think about it. Having the tap "backwards" will work if you have two fuses in the tap, but that is not the way it was designed to be used. You're likely overloading the bottom fuse if you are doing it backwards. @Moby, thanks for helping me understand this better.)

 

[greynolds]

Regarding the "wrong" option, the question is if the wiring can handle more load than the original fuse that's installed as the fuse should that is used should be sized for the load it is protecting and the wire that's feeding the fuse should be able to handle at least what the fuse is rated for. So the real question is how much additional load can the wire that's feeding the fuse block handle? You definitely don't want to get into a situation where you're tapping off of a fuse rated for 30 amps and adding another 30 amp load on the tap side for a total of 60 amps (I realize the taps aren't rated for 30 amps, I'm just using this to make a point). The only real risk in plugging the tap in the wrong way is that you're going to be much more likely to blow the factory fuse if both the factory load and the added load are drawing power at the same time and exceeding the rating of the factory fuse.

I think the bottom line is that these fuse taps should only be used for things that draw a small amount of current so that there's minimal risk of exceeding the rating of the wire that's feeding the fuse socket. Anything that requires more than a "few" amps should be wired to the battery and use a relay off of a tap if you need an ignition / accessory feed to make sure your accessory isn't running when the ignition switch is shut off. Feeding the tap into the switch side of a relay won't add much load to the stock fuse location.

 

[Moby]

@greynolds - completely agree with the load. That's what I was saying above that I actually prefer the "wrong" way with the stock fuse. The stock fuse size keeps one from overloading the wire. Also agree on you point about ideal usage. I pretty much only use fuse taps to trigger relays. In the photo above I have both the relay trigger and the relay power on the 30 Amp fuse tap. But this is temporary use for a 750mA load. When I add load I'll run a new power wire from the battery through the firewall. But I'm waiting to see if I have to cut the firewall to run a bunch of other wires or if I can get them all through one or two of the main stock gaskets.

@CharlieS - completely agree that there is a direction these are designed to work. And thank you for raising this topic. I certainly had never thought of this at all and I learned something as well.

Moreover this continues to be a great forum where we can discuss things like this and build knowledge. Appreciate all of the feedback. Cheers!