TR6 Overdrive Wiring Questions

[Gerry M]

I have a 1974 TR6 with overdrive. The wiring in photo together with vertically positioned solenoid (with one wire) suggests to me that it is an A-type OD. OD does not engage (tranny fluid has been topped up). What each of these terminal control? Is this OD wired correctly? With ignition turned on (car not running), shifter in 4th gear, and OD switch turned on, nothing happens. I am getting current at the Green wire terminals shown in photo but nowhere else. Its not shown in the photo but the Yellow wire is connected to a Red wire coming out of the OD switch and there is a purple wire coming out of the solenoid that connects to a Green/Brown wire that then connects to a Red wire coming out of the OD switch (so the OD switch connects to the solenoid and to the Yellow terminal neither show any current). I've been trying to figure this out for a while now. I would really like to get this OD working. What should I do?
PS: I don't know if this helps or just further complicates the problem. The Advance Auto Wire diagram for 74 TR6 does not show any OD relay and my car does not have one (just starter & horn relays). Isn't it the J-type OD that has no relay? Other than no relay everything else suggests that mine is an A-type OD?

 

[TR3driver]

Ok, the wiring seems a bit creative. You certainly might have an A-type, though I'm guessing it's not original to the car since 73 and later had J-types.

For an A-type, two of the switches should be wired in parallel. In your photo, those would be the two nearest the bottom of the photo. One of them is only closed when the gearbox is in 2nd gear; the other is only closed in 3rd or 4th. The switch near the top of your photo would be for the reverse lights (and only closed when the gearbox is in reverse).

Looks like the switch on the right is broken and will need to be replaced. They should all have two terminals (and the switch does not ground through the gearbox).

Here's a shot of the typical A-type wiring, from Dan's 70-71 diagram

(I believe some cars have the operating switch on the other side of the relay coil, but it doesn't really matter, the result is the same.)

The A-type solenoid draws a big chunk of current (like 20+ amps) every time it gets engaged, so it is probably best to stick with the factory wiring scheme (with a relay). I also found that my relay lasted much longer if I added a suppression diode across the solenoid (but no need to worry about that just now).

A photo of the OD would help verify that it is an A-type; but AFAIK all J-types have the solenoid mounted horizontal so you are probably correct about it being an A-type.

 

[Gerry M]

Have I got these switches labeled correctly(see photo)? How can I test to know if the switches are working?

 

[trrdster2000]

Gerry, these switches are really a safety switch to keep you from putting the car in reverse while the overdrive is engaged. Every time you change gears it cut the overdrive off. Get the proper wiring harness and a relay, you will be much better off.
If you have a "A" type , there is a arm on the opposite side of the solenoid that can be pushed forward to check the work or don't work part of the overdrive. This works the valve in the system. Get a passenger to do it with a pair of vise grips attached, it only needs to go forward enough for the hole in the case and the hole in the arm are equal.. Try it in third gear and if it clicks in you will feel it, and it must be held in place by a 1/8 inch drill to keep working, but I wouldn't do that. A very expensive add on, so do it right.

Wayne

 

[TR3driver]

Have I got these switches labeled correctly(see photo)? How can I test to know if the switches are working?

View attachment 34124

Yes, the labels look right to me.

One way to test would be to pull the wires off and connect an ohmmeter (DMM on ohms scale), or powered test lamp across the terminals of each switch in turn. You should get no continuity in neutral, or any gear other than the one that switch is supposed to detect. IOW, the 3/4 switch should be closed only with the gearbox in 3rd or 4th; the 2nd gear switch closed only in 2nd gear.

 

[Gerry M]

Thanks for the wiring diagram. I had the tranny out and it is now back in the car and I rewired it according to this diagram which makes sense when I look at the diagram but for some reason the solenoid is always energized with o/d switch turned on meaning that the overdrive will engage in reverse if I am not careful. This of course this would be catastrophic. Why does the o/d engage in reverse? How do I correct this ?
PS: the reverse switch on tranny does not share any wires with the 2 and 3/4 switches.

 

[TR3driver]

One of the switches must be making contact when the appropriate gear is not selected. Sometimes they need to be shimmed. These instructions specify 2nd gear, but the same process applies to the 3-4 switch

 

[Gerry M]

Not sure it’s the switch shimming but I will check that. I have wired according to drawing. With power on at the ignition switch I can activate the solenoid in all gears including neutral by turning on the overdrive column switch.

 

[Gerry M]

Here is the wiring diagram I have been working with. Looks the same as yours except mine shows a grounded solenoid. I don’t have a ground wire running from the solenoid. I figured it was self grounding. Could a grounded solenoid (not shown in your diagram) be the cause of my problem (i.e. two separate powered and grounded cuircuits - one for gearbox switches and one for solenoid)?

What would happen if I did this:
1. Disconnect solenoid from C2 terminal
2. Connect C2 to ground
3. Disconnect gearbox switches from ground
4. Connect single solenoid wire to gearbox switches
Im not good at electrical stuff but wouldnt that hookup ensure that the only way power gets the solenoid is through the 2/3/4 gears?

 

[TR3driver]

The solenoid grounds through it's mount. IMO there is no solenoid ground wire intended in the diagram I posted. It was just drawn a little strange. It does show the bottom of the solenoid grounded; it's just grounded to the same point (in the diagram) as the lockout switches. Think of it as an electrical circuit, rather than a physical wire. (Really, the whole "ground" concept on a car is just using the body of various components as one of the electrical conductors.)

Rather than trying to re-engineer the circuit without the relay (it is there for a reason), I suggest disconnecting each lockout switch in turn and retesting. If the solenoid still pulls in with both switches disconnected (and the wires left open), then there is a wiring error somewhere and you need to troubleshoot the wiring to the relay.

But most likely, IMO, you will find that disconnecting one switch will cause the solenoid to no longer activate with the column lever and the gearshift in neutral or reverse. That switch is staying closed when it should not be closed (associated gear/gears not selected). Unscrew the switch and, if it is still closed, it is defective. But again, most likely IMO, it will now be open, indicating that without a shim, it was sitting too close to the shift fork inside the gearbox top cover.

 

[TR3driver]

PS, the "pull-in coil" shown inside the solenoid draws a lot of current, something like 20 amps. The relay is there because the switches won't handle that much current (plus the inductive kickback) for long. It would probably work at first, but not for long.

In fact, my experience has been that even new relays "don't like" the inductive kickback, and I had several of them (including a fairly expensive reproduction from Moss) fail within just a few months to a year of daily driving. Adding a solid state diode to help absorb the kickback from the solenoid has made the relay (even my cheap "Made in China" brand one) last much much longer.