TR6 Overdrive Wiring
Dan Masters

Date: Sun, 12 Oct 1997 17:55:31 -0400 (EDT)
From: DANMAS@aol.com
Subject: Re: OD-TR-6

In a message dated 97-10-12 14:53:52 EDT, naffy@netins.net writes:
> If Mr. Masters could explain the wiring from relay all the way back to od it
> would be very helpful.

Be glad to, Gary. First of all, let's identify the relay, if you have one. From the factory, a relay was used for the O/D from the TR250 up to TR6 model year '74. Beginning with '74, the former O/D relay was confiscated to serve as a starter relay, and the O/D was wired direct. The following applies to the TR250 as well as the TR6.

As Triumph didn't always do what they said they did, or conversely, didn't always say correctly what they did, there can be descrepancies in the wiring configuration af any given Triumph. That said, look at the relays found on the inside of the drivers front fender, near the clutch M/C, and determine the color code of the wires going to them.

If the relay has one or two purple wires, one purple/black and one purple/yellow, it is the horn relay. If it has two purple/red, two green/red, two green/white, one light green/pink or green/brown, and one black wire, it is the hazard flasher relay. If it has one or two brown wires, one white/red, one white/orange, one white yellow, and one black, it is the starter relay.

If it is the O/D relay, it will have one white wire, one brown, one yellow/purple, and one yellow/green.

Next, look at the transmission. There will be two or three switches mounted to it, depending on the model year. One of these will be the reverse switch, which will have one green wire and one green/brown wire. The other switch(es) will be the O/D inhibit switch(es).

Since your car is a '69, with a '73 engine, you should have a relay, so we will start with that. The relay will have four or five terminals on it, labeled W1, W2, C1, C2, and if there is a fifth, it will be labeled C3 or C4. W1 and W2 are the terminals leading to the relay coil (W)indings (hence the "W"designation), and C1, C2, C3, and C4 are the terminals leading to the switch (C)ontacts (hence the "C" designation).

The power feed to the relay comes from the brown wire, (the brown wire is hot at all times and is not fused), which should be connected to the C1 terminal. Power to the solenoid from the relay comes from the C2 terminal, when the relay is energised, via a yellow/purple wire. Power to operate the relay coil comes from the white wire (the white wire is hot only when the key is on and is not fused).

All that is left now to get power to the solenoid is a ground connection for the relay coil. We have power to the relay contacts, power to the relay coil, and and a path from the relay contacts to the solenoid. When the other side of the relay coil, the W2 terminal, is grounded, the relay is energised, the internal relay switch contacts C1 and C2 will close (C1 and C2 are shorted together inside the relay), and the solenoid will be energised.

Two things are required to get the relay coil grounded - the O/D switch must be on, and the transmissiom must be in the proper gear. From the W2 terminal of the relay, a yellow/green wire goes to the O/D switch. From the O/D switch, a black wire goes to a connector. On the other side of this connector is a yellow wire. The yellow wire then goes to one of the inhibit switches, From there, it jumpers over to the other inhibit switch (it doesn't matter which one is which, for our purposes). The O/D switch is not polarity sensitive, so it doesn't matter which way it is wired - ie, the power could go to the black wire, and then through the yellow/green wire to the inhibit switch(es). The same is true of the inhibit switches - it doesn't matter which terminal is which.

There is a black wire from the other side of the inhibit switch, which goes to groud and to the other side of the other inhibit switch. Since the inhibit switches are wired in parrallel, if either one of them are closed, there will be a ground path up to the O/D switch. If the O/D switch is in the ON position, the ground path will continue to the relay terminal W2, and the relay is energised, operating the solenoid. If the transmission is not in one of the "correct" gears, neither of the inhibit switches will be closed, and the ground path is broken. In the correct gear, at least one will be closed.

What if you don't have a relay, or prefer not to use one? This set-up is even simpler. If the car came without a relay, power to the solenoid takes the following path: power is supplied by a green wire (green wires are hot only when the key is on, and they are fused), which connects to the yellow/green wire from the O/D switch, through the O/D switch, via a black wire, to the connector and a yellow/green wire, to the switch(es), wired as before, and then to the solenoid. It is important to note that the inhibit switches go to the solenoid and NOT to ground, as they did when the relay was used. If they are grounded, there will be a dead short from the green wire fuse to ground - not good!

If you wish to eliminate an existing relay, just rewire the car as above, using whatever color of wire you have available. The inhibit switches and the O/D switches are the same in either case. To test the solenoid just jumper directly from the battery with a large wire. Watch carefully for a shorted condition so you can remove the wire quickly if there is one. If the solenoid is OK, you should hear, or feel, it operating - there are no other interlocks involved.

Hope this was of some help to you. If I left anything out, or you need anything else, please let me know.
Dan Masters, Alcoa, TN