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A couple of TR# questions

Sounds like you are on the right track. Likely my next step would be to connect a test light from power (W1) to the disconnected yellow/green; and then start checking voltage along that circuit.

With the lockout & operating switches closed, the test light should be on brightly and nearly 0 volts from the yellow/green to ground. From your description, I would guess that you'll find closer to 6 volts. A bad lockout switch would be my top candidate, but it could also be something else, so do the test. On my Stag, I eventually discovered that a quick connect was not making consistent contact even though it snapped into place. There was just a tiny bit of play once it snapped in, which was enough to make operation intermittent.

If you get down to where there is ground on one side of the lockout and not-ground on the other side; remove the switch and check again. It might just be that the switch was not properly installed and is being held partially open. They are supposed to have washers added, to get them the right distance from the shift forks inside the housing.

One other thing, the factory OD wiring on TS39781LO did not match the diagram Geo gave. Instead, the operating switch was on the hot side of the relay, which winds up being simpler (one less wire running from the relay to the dash). My point is just to not assume that your wiring matches the diagram.
 
Agree, sounds to me like (for whatever reason) that circuit is not providing a good ground.

If you have the tunnel off (can't recall if you do) I would bypass each step in that yellow/purple circuit to see if skipping on of the cut-outs or the switch itself cause the relay hesitance to clear up. Then perhaps you'll know which part is not providing a good ground path.

Of course, you're actually in gear (not 1st or reverse) while you're testing this.

If bypassing each component brings no joy then I'd examine each connection, then each length of wire.
 
Thanks for the quick response guys.
I will proceed as detailed.
The tranny cover is attached, Grrr. I wonder how big a sin it would be to cut a nice neat access panel right above the interlock switches. Hidden from view by the carpet, nicely gasketed to keep water from splashing up later. Hmmm, I think I may become a sinner!
Tim :smile:
 
Tim - That's what I did for access to the solenoid on my early TR3A as well as for the oil fill plug on a later TR3A that I restored. Here's mine for the solenoid. I use a spare large rubber plug from the jack hole and two smaller rubber plugs you see up above for my very long screwdriver to gain access to the two slot-head screws which secure the body of the solenoid to the base casting of the overdrive.

But during the 52 years that I have owned my 1958 TR3A, I never had a problem with the isolator switches.
 

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It's your car, of course, Tim. But what happens when it turns out to be the ground lead to the lockout switches that is broken internally?

I try to avoid the swiss cheese effect wherever possible.
 
OK, victory at last!
I dint get a chance to continue the diagnostics until this morning, but often it works better for me to chew things over in the back of my mind a while. The broken wire scenario, or bad connection etc just didnt work for me, as they would not have produced the buzzing relay symptom. It dawned on me that I must be somehow backfeeding power into the relay, causing it to buzz. I followed the harness from the OD switch, it ends and connects to another harness. There is where I found the problem. I had used a double connector, to connect the 2 harness's together, not thinking that the 2 positions in the connector were common. DUH! It did make a neater appearance, but I guess function is more important. Anyway, an easy fix, and no illegal access holes were created!
Thanks everyone for the help working through all of the questions.
I now have a very rare thing, an English car with all of the electrical components working!
Thanks again,
Tim
 
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