Overdrive Wiring

[Doig]

Yes the much vaunted gbox swap is finally going ahead.

However as I'm swapping from non o/drive to o/drive box the wiring has me slightly befuddled.

I'm guessing the hexagional plug on the top of the unit is the inhibitor switch for the overdrive, which wires are meant to lead to this?

Also the replacement gbox has two green wires leading toward the front of the car I presume that this is the power source for the o/drive where exactly do these wires attach to and if they need extensions what sort of wire do I use? (sorry for these sorts of questions but I'm the sort of person whose happy to use electricity but has no idea how it works)

If anyone can help with these questions I'll appreciate it greatly, I'll try to post some pics tomorrow so you have some idea what I'm talking about.

Cheers

[Ash]

http://www.triumphspitfire.com/images/wiring/overdrivewiring.pdf

Hope this helps.

[Glenn]

The green wires will be for the reverse light switch on the side of the gearbox.  They should join 2 green wires coming from the loom under the washer bottle.  I'm assuming you have a Mk2 here.

I had to wire my O/D from scratch about a year ago, I didn't have much of the original wiring left.  Not to worry - replacing 30 year old wire and connectors with nice new ones can only make the car more reliable.  If you don't like wiring diagrams here's what I did (and please correct me if I remember wrongly folks):

You need a Lucas relay, the same type as the horn relay.  When you've finished the job completely you should screw this to the bulkhead alongside the horn relay, just above the fusebox.  The "W" terminals on the relay operate the low current (switching) side of the circuit.  The "C" terminals operate the bigger current which actually powers the overdrive solenoid and needs nice beefy wire.

W1 on your new relay connects to the ignition switch (originally using a white wire).  To do this connect a wire from W1 to one of the left hand terminals on the fuse nearest the top.  You may need to snip off the old lucar connector and fit 2 wires into a new one.  Solder the wires to the connector if possible.  Run a wire from W2 to one side of the IN/ OUT switch on the gear knob (originally yellow/ green).  From the other side of this switch run a wire (originally yellow) to one side of the inhibitor switch on the top of the 'box.  The other side of the inhibitor should be connected to a good earth.

Now the relay will be energised if the following conditions are met: ignition switch on, gear knob switch set to IN, in 3rd or 4th gear.

C1 on the relay connects to the starter solenoid.  Run a fat wire from C1 to one of the left terminals on the bottom fuse (brown wire).  Connect C2 directly to the overdrive solenoid using a fat wire (originally yellow/ purple leading to purple).

Now when the relay is energised, the overdrive solenoid should get a nice healthy current.

If you bypass the inhibitor switch by running the yellow wire from the gear knob straight to earth you can get overdrive in second (and of course first and *BANG* reverse).  Sounds a bit risky to someone as forgetful as me.

However I understand you can remove a blanking plug somewhere and install a second inhibitor switch to give you overdrive in 2nd.  Can anyone enlighten us?

Cheers,
Glenn

[Doig]

Think I've got it sorted now. still a few questions though.

Luckily the car used to have an overdrive so I already have the relay wired in.

What would be a good earth for the other side of the inhibator switch? as I have said I rubbish with electricity

Also what rating of wire should I use to power the solenoid?

Tried to get a picture in but it didn't work, wiring in box as i received it was a bit of a mess looked like somebody had just connected any loose connections to each other in order to ship it.

Cheers

[Doig]

Heres the pic you can see why I was so confused, the column switch is wired through the reverse switch all in all its a right mess and made very little sense

[Glenn]

I wonder if it's been wired without a relay.  It looks like a feed has been taken from the live side of the reverse light circuit.  This goes to the inhibitor, gearstick then direct to the O/D solenoid.

It looks like you could get this to work by connecting the yellow wires to the inhibitor on the top, connecting the green wires to the reverse switch on the side and the spare green wire to the overdrive solenoid. The solenoid should be earthed already with a black wire to an eyelet around one of the overdrive bolts.

Maybe that's how it should be?  Both my cars' wiring has been well messed about with so I really don't know.  Can anyone advise???  To relay or not to relay?

The manual says that the Solenoid operating current is only 1 amp so this would work.  However it also says that when it fails it can draw 20 amps which could  cause a fire as the gearknob switch is pretty weedy and the wiring that runs up the stick is very thin.

Might be safer to use a relay then.

[Glenn]

[quote by=Doig link=Blah.pl?b=2000,m=1140506046,s=3 date=1141028341]What would be a good earth for the other side of the inhibator switch? as I have said I rubbish with electricity
[/quote]

You could run a short lead to an eyelet.  Undo a convenient nut on the gearbox and fit the eyelet to the bolt.  Keep everything clean when fitting, lots of WD40 and a toothbrush.

[quote by=Doig link=Blah.pl?b=2000,m=1140506046,s=3 date=1141028341]Also what rating of wire should I use to power the solenoid?
[/quote]
About the thickness of a wire in your kettle/ hoover flex.  In fact if you have some lying about why not use a bit of brown wire.  No body will know you didn't buy it specially in the car shop.

Make sure you attach the connectors to the inhibitor before you fit the gearbox as I think it might actually be impossible to do otherwise!

[Doig]

Thanks for the help.

I've got the box all wired up now was hoping to run a current through it yesterday to check that the solenoids working before I put it back in.

I have two wires(both white with green stripe, one male one female connector) that have been disconected below the washer bottle in the engine bay, they are taped to the two green wires that connect to the reverse switch. Would I be correct in assuming that these power the over drive (the car originally had o/drive but was changed to 4 speed at some point.) Was going to get the multimeter out to check they ran from what I assume is the relay above the fuse box but couldn't find the damn thing.

I have one relay above the fuse box and a green see through plastic thingy which I assume is another relay (perhaps not original). I don't see any reason why the relay would have been removed when the gbox was changed. So I hoping its all still in there.

Thanks everyone for all your help so far

PS car is 75 2500TC (soon to be o/drive hopefully)

[Richard B]

If it is a J'type O/D then you do not need the relay; as the solenoid does not draw a lot of current. If you have an A'Type O/D then you need the relay as the solenoid draws sufficient current to burn out the O/D switch.

With a J'type; the single wire takes a live feed off of the reversing light switch, through 3-4 Inhibitor switch, through the O/D switch on the Gearstick and then to the solenoid. (Hope that makes sense?)

With an A'type; the wire that switches the relay goes through the 3-4 Inhibitor switch, through the O/D switch on the gearstick and then to earth. The switched feed from the relay goes direct to the solenoid. (clear as mud?)

[Doig]

Oh dear I must have wired it wrong. Its a J type you see. I have wired it up A type style as these were the only diagrams I could find. I had it on the road last night and the unit worked although only once in third gear. and hasn't again since.

Did J type cars not come with a relay or do they just not need them. My car had a relay which related to two spare spades under the washer bottle so I used these in wiring A type style. Now I'm only more confused and I hope I haven't done damage by having the unit wired incorrectly.

[Richard B]

I doubt that you have damaged the unit, so long as you haven't had OD engaged whilst in reverse (thats bad Karma). 

J'type cars do not have relays fitted as standard nor do they need them. It's only the A & D types that need a relay.

It makes the wiring simpler and cheaper believe me. However if you have the A'type wiring working correctly on a J'type solenoid, there is no harm done it's just a bit more complicated. I'm afraid you'll have to jack the car up and check the connections with a multi-meter.

[Doig]

Talked to my mechanic about this yesterday. He reckons the relay I wired into was a hangover from the PI fuel pump days. Explained to me hopw to wire it correctly but I'm sick and tired of the bloody thing, so hes going to do it for me at $45NZ which I thought was quite reasonable, at least then I'll know for sure whether I've buggered it.

He didn't think that it would have worked in reverse but I'm still concerned. The box made some strange noises in reverse when first engaged but then reverse gears often do that. I've disconnected all the wiring now so I'm sure its not on.

If the odrive goes into reverse does the whole box stop working or just the overdrive? Its working fine in its regular gears at the moment.