overdrive

[Cerberosa]

Hello

Hi all my overdrive has suddenly stopped working (yay!) on my 71 GT6 Mk3

The is no noise switch noise when it is engaged like you would normally here.
The reverse lights have also stopped working but work if i put power to the circuit.

I had a look at my overdrive relay, and found that the Yellow and Purple Wire that goes to overdrive solenoid does turn positive once the overdrive switch is engaged, does this mean i have a faulty relay, or it could be shorting out somewhere?

Or one of many other problems, im not very good at wiring yet.


cheers aidan

[rotoflex]

Use some scrap wire & run +12v from the battery to the wire on the solenoid just to make sure.
If you hear no clack when the solenoid wire gets 12V, you need a new solenoid (or the wire is broken).

It is assumed that the solenoid is getting its - connection from the battery as it should.
You could check with a meter to make sure the metal solenoid battery has continuity with the frame of the car or the 12v- side of the battery.  If you don't know how to check continuity with a cheap meter, let us know.  It is easy.

No reverse lights does sound like the reverse light switch has gone bad on the gearbox.  That happens!  Although it is interesting that you have had two things go bad on the gearbox at the same time.  The reverse light switch does not require a ground at its position, so if you disconnect the 2 wires from it and hold the ends of the wires together, the reverse lights should come on if the ignition swithch is in the "on" position.  While doing this test, remember not to leave the switch in the "on" position for too many minutes with the engine not running, or the coil can be damaged.  A short time is OK.

[Cerberosa]

Thank you this was a great help!

I put power to the the solenoid through the circuit and it clicked, So im assuming that is the relay gone and have ordered a new one.

The reverse lights are working if i put power to them but not when i engage reverse, i pulled the gearbox cover of and tried what you suggested but nothing happened this might have been down to a bad earth which i sorted then forgot to do the test again, i have ordered a new switch anyway.

This would all happen just coming up to my MOT!!

cheers

[heraldcoupe]

The reverse light and overdrive share a power feed, I'd be checking this before spending money on new parts,

Cheers,
Bill.

[cook1e]

Reverse lights are not part of the MOT test FYI. I had a wiring fault for several  years on the GT6 stopping the reverse lights working and it never failed an MOT while they were not working at more than one test centre.

[rotoflex]

heraldcoupe wrote:

The reverse light and overdrive share a power feed, I'd be checking this before spending money on new parts,

Good point, do your brake lights work?

Here is a GT6 Mk3 wiring diagram (cursed Flickr & Photobucket redesigns are making fullsize photos problematic):
http://www.sendspace.com/file/fq10ok

Points of interest are connectors 3 & 4 on the back of the ignition switch.  That's where the connections at the lowercase "a" & "b" in the overdrive wiring inset come from.

Sort of hoping here that the overdrive was wired as per original factory design.  Many overdrives were installed after manufacture, & the wiring is sometimes drawn from strange inspirations.

It might be more surefooted to first resolve the reverse light problem.
When the ignition switch is on, do you have 12V between ground & the solid green wire connected to the reverse lamp switch?
Do you have a meter?  They are inexpensive.

[Richard B]

rotoflex wrote:

Sort of hoping here that the overdrive was wired as per original factory design.  Many overdrives were installed after manufacture, & the wiring is sometimes drawn from strange inspirations.

Normally J Type O/D is fed from the reversing light switch. It could well be a "son of Frankenstein" wiring loom.

As the reversing llights do not work I would look there first.

[Pete Lewis]

and dont forget the wires up the gear stick are notorious for shorts and heat/fatigue breakage
  if these ever need replacing use a silicon sleeved wire from maplins or elswhere, better in hot surroundings .

Pete

[Velocita Rosso]

peterhlewis wrote:

and dont forget the wires up the gear stick are notorious for shorts and heat/fatigue breakage
  if these ever need replacing use a silicon sleeved wire from maplins or elswhere, better in hot surroundings .

Pete

Thin wall cable ,as used in moderns,is the best

[rotoflex]

So a question would be:
Do you have one gearbox switch for the reverse lights, & another for the overdrive inhibitor switch,
or just one gearbox switch connected to both?

[Cerberosa]

Hi all

thanks for all the replies! all appreciated

My circuit appears to be as the manual states.
My overdrive troubles to be over, seems the relay had gone. However before fitting the new one i did check if my brake lights were working, which they wernt.

I checked the wires to the button along the gearlever an they are not damaged
After fitting the new relay all the above problems seem to have stopped, this might be because i checked the brake light connectors at the pedal as they may of come loose when i took the gearbox tunnel of. But i do suspect a bad earth at the rear.
My reverse light is now also working, so happy days! Hope thats it for now

Thanks again

Aidan

[rotoflex]

I don't understand these damn cars either.