BWM Brown Wire Mod 3rd Gen

[JCUZ]

I ended up connecting the wiring to the wire at the transfer case - ran the wiring through the fire wall, then down the back of the motor, away from the exhaust, and along the gearbox to the transfer case. It took around 6m (20ft) of wire to go from the relay & switch to the transfer case (one 3m/10ft length there, and one 3m length back).

The only issue I have is that I was expecting the light on the switch only to light up when 4WD was actually operating. So far, I haven't driven it, but the light is on when you start the truck. Is the default setting when using 4WD auto to be in 4WD, and it actually only turns off (reverts to auto 2WD) when you are actually moving? If so, then it should be right - if not, then I've wired something up wrong, but will check with a circuit tester tomorrow. I'll also check the turning the switch off forces 2WD.

 

[JCUZ]

I ended up connecting the wiring to the wire at the transfer case - ran the wiring through the fire wall, then down the back of the motor, away from the exhaust, and along the gearbox to the transfer case. It took around 6m (20ft) of wire to go from the relay & switch to the transfer case (one 3m/10ft length there, and one 3m length back).

The only issue I have is that I was expecting the light on the switch only to light up when 4WD was actually operating. So far, I haven't driven it, but the light is on when you start the truck. Is the default setting when using 4WD auto to be in 4WD, and it actually only turns off (reverts to auto 2WD) when you are actually moving? If so, then it should be right - if not, then I've wired something up wrong, but will check with a circuit tester tomorrow. I'll also check the turning the switch off forces 2WD.

It's all good. I had it wired correctly, but did some testing on voltages and amps - the brown wire carries around 1 to 1.5V when inactive (and about 2 amps). When 4WD is actually engaged, this increases to around 2.5V and 3.5 Amps. So there is absolutely no need to wire in a relay at all - you can simply go straight through a switch (most basic switches are rated to 12V and 10Amp). In fact I found the 12V 30Amp relay I was using was buzzing when 4WD was on and engaged - so I don't think it would actually be working properly as it's in a constant state of cycling on/off due to not enough power going through it. I guess if you could get a 3V 5amp relay, then it might be worth installing one, but at that low voltage, it is totally unnecessary.

If you use a lighted switch, the the switch will illuminate (though it's quite dull) when the switch is on but 4WD is not engaged, but when 4WD engages, it lights up about twice as bright, so it can actually be used to determine when 4WD is operating, and when it's not.

Of course, turning the switch off means there's no light, and is forced into 2WD mode, which is what the whole mod is about in the first place.

 

[ktford]

well done cus, how bout tipping our hats to those pioneers who went to all the hard efforts in the 1st place. Thanks guys
Scotty

 

[JCUZ]

well done cus, how bout tipping our hats to those pioneers who went to all the hard efforts in the 1st place. Thanks guys
Scotty

For sure - wouldn't have done it without their write up, and wouldn't have known which wire to cut without the call to you - so thanks all!!!

It's fun getting it sideways on dirt now!

 

[whitestang04gt]

I have hooked everything up, except the actual cutting of the brown wire. Instead of grabbing power for the switch from another wire, I have jumped the switch power from the transfer wire (connection 30 on the relay) - this way, instead of the light lighting up all the time, it will actually only light up when the Auto 4WD kicks in, so I'll be able to tell when it is actually operating in 4WD mode (unlike now, where you don't really know).

Of course, with the switch off, it will just be 2WD, as intended.

Wiring Summary
At transfer case
"From" transfer wire - to pin 30 on the relay, and "source"/+ve on the switch
"To" transfer module brown wire to pin 87 on the relay

relay
pin 87 on the relay goes to the "To" transfer module brown wire (ie bit closest to the transfer case).
pin 30 on relay goes to "from" transfer module brown wire (the other end of the brown wire cut near the transfer case)
pin 86 on relay goes to "load" pin on switch
pin 85 goes to earth

switch
load wire on switch to pin 86 on relay
ground pin on switch to earth
source/+ve pin on switch to transfer module "from" wire (via pin 30 on relay)

Doesn't the normal wiring on page one do the exact same thing? The led light should come on when switched to AWD based on the wiring diagram posted. OR am I missing something?

 

[JCUZ]

Doesn't the normal wiring on page one do the exact same thing? The led light should come on when switched to AWD based on the wiring diagram posted. OR am I missing something?

Yes, but as it's just the wiring off one switch, I don't think it would work when you select 4WD High or Low (but I'm no expert, so not 100% sure).

Regardless, you probably don't need, and actually shouldn't use, a 12V relay, as there is not enough voltage to keep a constant circuit open in the relay. The voltage changes from under 2 to just under 3 (and amps from 1.5 to 3 ish), so no relay is really required - just a standard 12V 10Amp switch with each side of the switch going to the cut wires from the transfer case will do the trick.

 

[whitestang04gt]

Yes, but as it's just the wiring off one switch, I don't think it would work when you select 4WD High or Low (but I'm no expert, so not 100% sure).

Regardless, you probably don't need, and actually shouldn't use, a 12V relay, as there is not enough voltage to keep a constant circuit open in the relay. The voltage changes from under 2 to just under 3 (and amps from 1.5 to 3 ish), so no relay is really required - just a standard 12V 10Amp switch with each side of the switch going to the cut wires from the transfer case will do the trick.

Thats kind of what I was thinking but wanted to make sure. I need to install so I can get it on the dyno.

 

[JCUZ]

Thats kind of what I was thinking but wanted to make sure. I need to install so I can get it on the dyno.

Me too - I always wanted to do this, but dyno day on the 24th means that I had to do it now to be ready!

You could always do what ktford did and just cut the wire at the transfer case - it will be full time 2WD, until you rejoin the wire, or put a switch in so you can select 4WD/2WD.

 

[whitestang04gt]

Me too - I always wanted to do this, but dyno day on the 24th means that I had to do it now to be ready!

You could always do what ktford did and just cut the wire at the transfer case - it will be full time 2WD, until you rejoin the wire, or put a switch in so you can select 4WD/2WD.

Let me know how your dyno turns out & how big of a difference you feel with it in 2wd. thanks

 

[JCUZ]

Let me know how your dyno turns out & how big of a difference you feel with it in 2wd. thanks

In 2WD, it is happy to step the tail out on any slippery surface (wet road, dirt, etc). That's the only real difference I've noticed. As for the dyno - not expecting heaps - around 130rwkw (180hp??), but am more interested in the power difference between LPG and petrol.

 

[ktford]

Mine showed 164rwhp about three weeks ago with 36,000 k's on the clock
Scotty

 

[JCUZ]

Mine showed 164rwhp about three weeks ago with 36,000 k's on the clock
Scotty

Wow - 201 less than the turbo; you must be missing it!

It's in the ballpark of what I'd expect, so if I get around that, I'll be happy enough. And if I don't, then too bad, cos I won't be throwing any money at it chasing silly power (though maybe a Kenne Bell would go OK????!)

 

[Mountaineer01]

I have a 2002 mercury mountaineer AWD. I am kinda confused on what exactly this MOD does. If you have 4wd in your ex why would you need a 2wd switch when you can just turn the 4wd off in the dash? this is confusing

 

[JCUZ]

I have a 2002 mercury mountaineer AWD. I am kinda confused on what exactly this MOD does. If you have 4wd in your ex why would you need a 2wd switch when you can just turn the 4wd off in the dash? this is confusing

Because there is no way to turn the 4WD off. Apparently, it is available as a DFO (Dealer fit option), which pretty much is the same mod we are doing here, apart from a "better" switch.

This mod should also work on your AWD, though you may not get the benefit of the 2WD Lo.

 

[Curtis]

Because there is no way to turn the 4WD off. Apparently, it is available as a DFO (Dealer fit option), which pretty much is the same mod we are doing here, apart from a "better" switch.

A dealer fit option (DFO) ?
Really?
Anyone on here have a pic of that switch? You may be able to buy one if we had a part number.

And if the dealer would install such a mod, it cant be a harmful mod as suggested by some in how spinning the rear wheels could hurt the transfer case.

Anyone else think the same?

 

[carney64]

Has anyone kept track of the MPG they got after this mod? I know there were a few estimates, I didn't know if anyone had any hard numbers. Thanks

 

[ktford]

I think it is quite minimal, my figures are invalid as I combined the install with bigger tyre fitment
Scotty

 

[Blanketman]

ktford
where about behind the glove box did you tap into the wire??
as my car is a little bit apart (only drivers seat remaining)
i thought of trying this mod

 

[JCUZ]

ktford
where about behind the glove box did you tap into the wire??
as my car is a little bit apart (only drivers seat remaining)
i thought of trying this mod

ktford and I both cut the wire right at the transfer case. There are so many wires going into the 4WD module near the glovebox that it was just too confusing. At the transfer case, there is a plug with about 6 or 8 wires, and a few of them are brown, but the brown one you want is about twice as thick as any of the others, and it goes into the back of the transfer case. Have fun with it - 2WD can be fun (on the dirt!!).

 

[Blanketman]

thank you
will do it tonight