Overdrive Wiring

[Duncan Elliott]

Hi,

 

I am just in the process of re-assembling my 4A following a bit of a facelift and have just noticed that the overdrive wiring isn't connected.

 

Can anyone give me any pointers on how they are wired up - I have found the wiring for the one at the back (closest to engine) but can't locate anything for the other one.

 

Any input would be greatly appreciated.

 

Thanks

 

[littlejim]

Here is a bit from the wiring diagram one of the forum members did for us, Ian Cornish I think, apols if I got it wrong.

 

Edited November 28, 2009 by littlejim

[Steve Knight]

That diagram looks confusing. First you need to know which switch on the gearbox does what.

Would the centre one be the 3/4th overdrive limiter. while the other is the reversing light. When using the original engine bay relay, the gearbox switch powers the negative(-)latching of this relay ( via the dashboard switch ) which then sends a positive feed direct to the o/d solenoid. Later Triumph models wired the o/d(+) direct from the dashboard switch(+), I do not think they were even fused. A wiring diagram from your workshop manual is essential, as it shows all the colours used through-out the car.

Edited November 29, 2009 by Steve Knight

[tthomson]

Hi Duncan,

 

The overdrive switches are just connected in parallel, and since they are not grounded through the screw fittings, it doesn't really matter which way around they are connected. Just wire one connection on each to ground, then wire the other two connections together and then connect these back to the black wire on the column mounted overdrive switch. The other end of the overdrive switch has a yellow wire that connects via a bullet to a yellow/green wire back to the relay W2 connection.

 

If the relay is wired in properly, it will connect C1 to C2 when the overdrive switch is closed when it is on 2nd, 3rd or 4th gear (ie activate the solenoid).

 

There are various websites showing the position of the various gearbox switches including the reverse switch.

 

Good luck

 

TT

[ianc]

There are 3 bosses shown in Duncan's photo, the one on the left (looking forward in the vehicle is unused).

Think about the gear lever: to engage reverse, one moves the lever to the far right, which engages the leftmost selector, which lies beneath the boss which has no switch. So, there's no switch for a reversing light - normal on a TR2/3/4.

With the gear lever in the central position, one can operate on 3rd & 4th gears using the central selector fork, which lies beneath the switch on the centre boss.

With the gear lever in the left position, one can operate on 1st & 2nd gears using the rightmost selector fork, which lies beneath the switch on the righthand boss - this switch will operate on 2nd gear only.

All this can be checked very easily with a multimeter or a bit of wire from the fusebox and a bulb.

Ian Cornish

[Duncan Elliott]

Thanks for the input,

 

For clarification though... is the boss towards the rear of the car for the reverse light ?? this one wasn't wired up to anything anyway. I asumed it was the OD for either 3rd or 4th gear ?

 

 

 

Thanks

[ianc]

In Duncan's photo, showing just the top of the gearbox, with two switches and an unused boss, the clutch housing lies at 11 o'clock, and that's toward the front of the car.

- the switch with a single wire is 3rd/4th,

- the switch without a wire is for 2nd,

- the boss is there for an optional reversing lamp switch (although I cannot say whether the selector fork would have the necessary lump to operate this, were it to be fitted).

Think of it this way: as you select 2nd gear, the gerlever is pushed to the LEFT and back, and this (because there is a pivot point on the gearlever) operates the selector fork on the RIGHT of the gearbox.

Ian Cornish

[Duncan Elliott]

Thanks once again for the assistance,

 

As I have located the correct wiring for 3rd/4th OD, can I simply daisy chain the boss for 2nd to the 3rd/4th boss ?

 

 

Excuse my ignorance here.... auto electrics is somewhat of a dark art to me :-)

 

 

 

 

Cheers

[ianc]

Depends what you mean by daisy chain.

The switches need to be connected in parallel (see diagram posted by Little Jim).

The wire coming from the overdrive switch needs to be attached to one connection on BOTH isolator switches.

From the other connection on BOTH isolator switches, you need a conection to a good earth (chassis) - usually to a tag under one of the bolts holding down the gearbox top cover.

In this way, whichever switch closes, there will be an earth path for the current flowing from the ignition switch, via the relay coil (W1-W2), the overdrive switch (assuming it to be in the operated position) and an isolator switch (assuming you have either 2/3/4 gear engaged).

Ian Cornish

[Duncan Elliott]

Thanks for the replies - Can't understand why they were disconected in the first place though...

 

Anyway, I will wire them up and see what happens.

 

 

 

Cheers

[Smokey]

The switches might have been bypassed because someone connected the wiring directly without using them, so that the column switch turns on the overdrive regardless of gearshift position. Very dangerous, because if you forget and leave the overdrive on in reverse, that's the end of the overdrive. A small possibiliy, but check to make sure that the switches were not bypassed with a direct ground from the relay.