Visit our Twitter feed for more great content
TRExp

Spitfire & GT6 Forum

J-type overdrive wiring question

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

Brad N Avatar
Brad N Silver Member Brad Newman
Sanford, NC, USA   USA
I have a 1972 Spitfire Mk 4 which I brought over from the UK. It's a J-type transmission and I was tired that the overdrive was not working. I pulled the tunnel cover out and now I see why. Nothing is wired correctly or at all. What a mess. Wiring diagrams are confusing and the wire colors don't seem to match what I would expect to see. So before I start unraveling the wiring loom, I have a couple of questions:

1. Is the 4 post relay on the top left the Overdrive relay? There are 4 posts/pins with a yellow/green and yellow wire attached but nothing else on the top 2 post/pins

2. Is the 2 post relay the reverse lamp switch and is the green and green/yellow wiring correct?

3. The overdrive solenoid is not even wired, except for the ground

I have searched all over the internet and this site to figure out how the wires should connect to each component (separate from the wiring diagrams which are not helping me right now) and I don't know which post should have which wire running to it.

Can someone help uncover this mystery for me and suggest the right next steps for me to take?

Thanks!

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

Attachments:
Transmission 10.jpg    61.1 KB
Transmission 10.jpg

Transmission 9.jpg    50.8 KB
Sign In or Register to view this photo
kaatmanduu Avatar
kaatmanduu Silver Member Mike Stevens
Grass Valley, CA, USA   USA
Brad N Avatar
Brad N Silver Member Brad Newman
Sanford, NC, USA   USA
Thanks for the quick reply Mike. I have seen this but I don't see the reverse lamp switch in this circuit though I understand it may not be part of it.

Is the switch in the 1st photo the reverse lamp switch or is it the overdrive gearbox switch?

I can only find 4 electrical points on the gearbox.

One I figure is the overdrive relay with the 4 pins, the 2nd is the overdrive solenoid, the 3rd is the on/out switch on the gearshift know. Those were easy. Is this last switch in the middle top of the gearbox the reverse lamp switch? I'm assuming it is and if that's the case, I must not have an overdrive gearbox switch. Is that possible?

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
They are switches. The one to the rear should be for back up lights, the one at the end of the extension (closer to the engine) should be the inhibitor switch, to prevent the OD being operated in reverse, First or Second gear.

You need not have any relays with a 'J' type O/D.

You might want to check your O/D solenoid by running 12v to it. You should here a click.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
Check that inhibitor switch on the top of the gearbox with a multimeter, you should get continuity across the terminals when in Tird or Forth gear. It could be wired wrong. But honestly I don't remember seeing one with 4 terminals?

That wiring is Fugly, marettes for goodness sake?

Best start afresh.

Brad N Avatar
Brad N Silver Member Brad Newman
Sanford, NC, USA   USA
Thanks Duncan - I'll check the solenoid.

So the inhibitor switch is the Overdrive Gearbox Switch, the 4 post switch in the new photo attached? It only has 2 wires to this switch - YG and Y which, color-wise, does not look to match up with the wiring diagram sent by Mike. Does this mean the other 2 posts aren't used. It sure is confusing!

One wire should be coming off the reverse switch to the overdrive switch according to the wiring diagram. To confirm this, in the absence of the right wire colors, I think I would need to unwrap the harness to see how the wires are/are not connected. Is this what you'd do?

It would be great to see how all the wires are connected in an actual photo without the harness wrap. I can wish.........

Brad


Attachments:
Transmission 12.jpg    59.9 KB
Transmission 12.jpg

Brad N Avatar
Brad N Silver Member Brad Newman
Sanford, NC, USA   USA
Agreed Tony. It's a real puzzle.......

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
The in hibitor switch needs only two wires power in and out.

I think it may be wired wrong, I think one wire should go to the top terminal. As I said, check continuity.

kaatmanduu Avatar
kaatmanduu Silver Member Mike Stevens
Grass Valley, CA, USA   USA
As I recall, the reverse circuit is completely independent of the OD circuit. On a high level, you have 12V into the 3/4 inhibitor switch, then that goes to the in/out switch, then to the solenoid. The wiring looks to be a bit 'customized'. When I put in my OD, I picked up a harness from, I think, British Wiring. I'll see if I can find the receipt when I get home.

Brad N Avatar
Brad N Silver Member Brad Newman
Sanford, NC, USA   USA
Thanks Mike. I think I'll unravel the wiring harness in that area to see what wires may be spliced to one another.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
The combination of the 3 rail gear box and 'J' type O/D was unique to 1974 (at least in North America)

According to my wiring diagram the power for the O/D circuit comes from the reverse light switch. Where the Green power goes to the switch another Green wire comes off to the inhibitor switch then on to the on/off switch then to the solenoid.

Seems the colours of wire change from Green to Black to Yellow & Purple along the way.

When I did mine I used a unique wire colour for the whole O/D circuit, it just seemed more intuitive.

macspit Avatar
macspit Malcolm M.
ictoria, BC, Canada   CAN
1969 Triumph GT6+ (MkII) "The Plum"
1970 Triumph Spitfire MkIII "Nothing Yet"
1976 Triumph 1500 "The Pickle"
1994 Mini Mayfair "The Min"
Check that inhibitor switch, both wires are on the same terminal - two spades on each terminal - 2 top terminals are common as are the 2 bottom ones. Probably need one wire top, one wire bottom. You need 12 volts to the inhibitor, from that switch to the in/ out switch on the gearshift then from that switch to the solenoid. Usually the 12 volts comes from the power feed to the reversing light switch on the J type as there is no solenoid on the firewall as with the D type. The 2 switches are in series so both have to be closed to engage the overdrive. Also check the operation of the inhibitor switch - on my GT6 it is operated by a lever on the 3/4 shift rod which closes the switch contacts. Can be out of adjustment.

Brad N Avatar
Brad N Silver Member Brad Newman
Sanford, NC, USA   USA
Tony/Mike/Malcolm:

Thanks for the detailed advice and instructions. Now you know how I'll be spending tomorrow. I'll keep you all posted.

Brad

Brad N Avatar
Brad N Silver Member Brad Newman
Sanford, NC, USA   USA
Did a little investigation before the day gets started........Good news, the solenoid engages with 12V applied. Haven't checked the inhibitor switch wiring/continuity yet but something seems a little strange and unexpected.

When the 2 black wires shown in the photo are touched, with the ignition on, it activates a relay on the firewall (other photo). In the photo, one wire starts yellow and the other is black. The other wire shown is yellow/purple with a brown wire bulleted connection (who knows why).

So I have:

- 2 wires to the inhibitor switch (that has 4 terminals)
- 2 wires to the reverse lamp switch (that has 4 terminals)
- only a ground wire to the solenoid (it's missing the 12V wire which should be coming from the in/out switch from the gearshift)
- and these 3 wires just hanging out there with one getting power when the ignition is turned on that somehow activates a relay

Checking switch continuity is the next step but could it be possible that the black wire with 12V be connected to an open terminal on the inhibitor switch then send a wire over from the other terminal to the in/out switch with the wire then going to the solenoid?

That would leave one black wire and the yellow/purple wire without a home. That makes no sense!


Attachments:
Transmission 14.jpg    41.9 KB
Transmission 14.jpg

Transmission 13.jpg    52.5 KB
Sign In or Register to view this photo
Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
As a 72 your car would have had a 'D' type O/D which would need a relay.

The wiring would have been quite different.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster