Outer Limits 4x4 Board

Wondering if anyone knows about the solenoids on the transfer case of new hilux/prado/surf that engages 4wd. I am trying to wire up that gearbox in my 84 lux. Seems to have 2 main wires (green & yellow) connect one to +ve the other to negative the 4wd engages. Then reverse the polarity and it disengages. Does this sound right and if so do I need a relay that can reverse the polarity when switched by button on gear stick?

It's possible that's how it works. The locking solenoid on the rear tailgate of my Feroza works that way.

I'll attach a circuit diagram below that is designed for use in a car alarm for central locking, but it could be modified easily to suit your purposes.

Instead of the top two wires being negative trigger lock and unlock, that would be your input for 4WD on/off (ie switch one of them to earth 4WD engages; switch the other to earth 4WD disengages- just make sure only one is earthed at a time!!)



Where the door lock solenoid is pictured use those two wire to your transfer case.

Simply get a rocker switch SPDT, and hook the earth to the centre terminal and the two wires for lock/ unlock ( used for 4WD on/ off in your case) to the outer terminals and it should work.

**** Having a think about it you should also add an electrolytic capacitor in series with each of the 4WD on/ off wires- that way you will only get a voltage pulse to activate the solenoid, rather than the voltage always being across it which could burn the windings out.

Let me know if you want anymore details.

Edit: mistake with switch type fixed!

I believe you will want a SPDT (single pole, double throw) switch to match the wiring diagram and description, not SPST (single throw.) I think you also want a momentary switch if I understand your description of how the t'fer case works. Otherwise you may burn out the solenoid.

Personally I would use positive switching not negative switching, as well. This is for the very good reason that if a wire shorts to ground and it's positive, it will blow a fuse, whereas if a wire shorts to ground and it's a ground-switching wire, it will actually trigger the circuit and cause 4WD to activate.

ie with negative switching a short circuit caused by a damaged wire or whatever can turn on 4WD unpredictably - dangerous.

Sorry to confuse things but I think it matters. If I get time tonight I will post an alternative diagram (unless Area54 gets in first.)

Note also that you could just use a DPDT switch and no relays, which would be cheaper and easier.

Jason

murcod wrote:**** Having a think about it you should also add an electrolytic capacitor in series with each of the 4WD on/ off wires- that way you will only get a voltage pulse to activate the solenoid, rather than the voltage always being across it which could burn the windings out.

Let me know if you want anymore details.

Yes, this is what I was getting at with the momentary switch. I think a momentary switch might be simpler, more reliable and easier to fix if something screws up.

Jason

Suddenly all the people with bright ideas pop out of the woodwork! I posted that idea up as nobody had bothered responding in over two days......

You're right the switch type should have read SPDT- my mistake. I'll edit the post and fix it up.

If you tried using a DPDT switch with no relays you're not only going to have to use a switch that can handle high current surges, but you'll also have the problem of the coil being permantly engergised.

Wiring that's done properly will never short out! That's what insulation tape, heatshrink and conduit were invented for!

Another idea (a lot simpler)- use a central locking control module to do the job. For around $20 plus a switch, fuse etc. It already has the circuitry built in to handle the surge currents, will only pulse the solenoid, will reverse the polarity as required and is self contained in a small plastic box ready to go.

Just use a SPDT switch on the lock / unlock input (normally white and brown wires) and wire the solenoid to the output (normally blue and green wires). Wire the power via a fuse and the earth to the chassis. The centre terminal of the switch once again goes to earth.

murcod wrote:If you tried using a DPDT switch with no relays you're not only going to have to use a switch that can handle high current surges, but you'll also have the problem of the coil being permantly engergised.

You'd use a momentary switch so the coils would not be energised.

I don't believe current handling would be a problem if you use the right switch [hint: if the wires to the solenoid aren't unusually thick, then the current load is not a concern] but if you really want to use relays you'd still use a momentary switch plus 2 DPST relays or 1 DPDT relay.

No offence but using capacitors for this would be overengineering even if it did work.

Jason

Thanks guys, that's all a bit confusing but I think I get your drift. Just have to read through it a few more times. I actually have the 4wd control module from the original wiring harness but I have no idea of how it was connected as many of the plugs have been chopped and it also controls the vacuum solenoids for the front diff. Mine has manual hubs however. Might be able to reuse this module with a bit of investigation. I guess it controls the pulse/switching.

Okay here you go.

Option 1: using 1 x DPDT momentary switch - this is familiar to you as an electric window switch.

Jaycar part # SK-0980, $6.95 ea

The red and black wires are bridged to the diagonally opposite terminals so that you send the power in one or the other polarity depending on which way you press the switch.

Option 2 requires:

1xSPDT centre off switch eg. Jaycar part #SK-0987, $3.95 ea. This is also a momentary - ie it only operates while you're actually pressing it.
2xSPDT horn relay (30A) Jaycar part #SY-4070, $6.95 ea

It looks a bit complicated but it really isn't once you look at the diagram for a while.

Someone tell me if I made a mistake.

I honestly think the switch alone is enough, and it's also more reliable as there are fewer parts to fail.

Anyway, aside from the electric window style switch you could also do a similar job with two separate push buttons or whatever, depending on how you want it to look.

And there endeth my good deed for the day.

Jason