TR2/3/3A Type A TR3 Overdrive Wiring

[BillyB62]

All,

Ok, I'm at my wits end and I'm sure I'm just missing something. The OD transmission was rebuilt this Fall from Quantumechanics and I've just finished the install as part of my long winter maintenance. Attached is the way I've currently wired the overdrive unit and although I can hear the relay click, the OD unit never engages. I've swapped my car over to negative ground and added an alternator (thus eliminating the Control Box). I've added another fuse box to accommodate fuse on other things like the radio & heater. I've replaced/purchased all wiring harnesses (the main harness and both the upper & lower OD harnesses) from British Wiring this winter. The red tabs on the picture show where I have power all the time.

I've tried bypassing the OD switch on the dash by connecting the Yellow/Green wire directly to the Yellow wire that goes to the Isolator switches on top of the unit. When I engage the switch (or bypass the switch), I do get continuity on the Yellow/Purple wire to the OD solenoid, but nothing on the Yellow wire going to the Isolator switches.

Any help both reviewing the diagram or suggesting anything that'll get it running again would be appreciated.

Thanks in advance,

 

[Geo Hahn]

I cannot tell how you have the isolator switches wired - they must be set up where either one can provide a path to ground but not such that both have to be depressed to get a ground. Like this:

Also - I assume when you say 'I can hear the relay click' you mean the small relay on the firewall (small click) and not the solenoid on the gearbox (big click).

 

[BillyB62]

Thanks Geo,

I think I have the isolator switches set up the same ways as you do. This might be a dumb question, but can I assume the isolator switch terminals are not polarity sensitive (meaning the yellow or black can connect to either side)?

You are correct, I hear a small click from the relay on the firewall, I hear nothing down below at all.

Much appreciated....

BTw - I used to be stationed at Davis-Monthan AFB - do you get much driving done in the summer?

 

[Geo Hahn]

The next thing I would try would be offering 12V directly to the Yellow/Purple wire to the solenoid and see if that causes engagement (loud click). This bypasses everything (relays, dash switch, isolator switches) to confirm that the solenoid is fine and possibly narrow the search a bit.

Sure, I still drive the cars many times throughout the week - either in the morning & evening or else staying above 7000'. High tomorrow... 'in the teens'.

 

[Chuck Murphy]

Bill, when I look at your wiring diagram I do not think you have the wires on the isolator switches hooked up correctly. I would think that with the wiring as you show it you would get solenoid action only when your gear is in second and not if in third or fourth (OR when you have shifted your gear into third or fourth and not if in second gear).
Chuck

 

[BillyB62]

Thanks to both of you for responding. I had a family function last night and I'm going to a show this morning so I won't get back to troubleshooting until tonight. Geo, I will apply direct current to he Yellow/Purple wire and report back. Chuck, what can I do to correct a mistake in the wiring that you suggest?

Thanks to all for the help, after waiting many years and being so excited to finally get an OD tranny, I'm a little discouraged that it's not working....but not too discouraged to not have a wonderful ride today

 

[chuck69ss]

Bill - Your wiring diagram looks OK, I think - as long as your white wire is hot only when the ignition switch is on, which it should be.

First thing - Is it positive or negative ground? I'm going to assume negative ground for following. If not, the method is the same, but voltage is negative with respect to the chassis. Note that I refer to chassis and ground interchangeably.

As Geo said, you can check the solenoid by connecting hot power directly to the yellow/purple wire. The solenoid should move with a good solid jump. You will need a fairly heavy wire as the initial pull requires several amps. The holding current is <1A. If it doesn't move, the solenoid is either bad, isn't grounded (not likely), or the OD actuation lever is jammed or misaligned. (Ground connection is through the solenoid body to the gearbox to the engine to the chassis through a ground strap.) This also means that your wiring from the1 relay to solenoid needs to be a heavy gauge.

If it moves, you can hook it back up and bypass all three switches by connecting chassis to W2 of the relay. If it doesn't move, then relay or wiring or fuse is bad.

You can test the remaining circuitry using a voltmeter or test lamp. You should be able to trace the voltage path on both sides of the relay. Check the primary side across W1 and W2 - you should see 12V with OD switch engaged and in 3rd or 4th gear and 0V with OD switch off or in any other gear.

You can check the secondary side of the relay as follows: Verify voltage at C1 to chassis. Verify that with OD switch on and in 3rd or 4th gear, there is voltage at C2 to chassis. No voltage when any switch is open.

 

[Chuck Murphy]

Bill, after a second study I think your wiring is OK after all. Sorry for the confusion.
Chuck

 

[Geo Hahn]

...This also means that your wiring from the1 relay to solenoid needs to be a heavy gauge...

The current drawn by the pull-in coil is high (20+ amps?) but only lasts a fraction of a second so in my experience the wiring does not need to be especially large - in fact I have an 8-amp fuse (slo-blow) on the line. If the solenoid ever fails to cut the pull-in current immediately something is going to get cooked -- fuses (and even that wire) are cheaper than a solenoid.

 

[KVH]

Geo, do you have an easy way to send a pic of your wiring with that in-line fuse? I want to do that on my 4A.

 

[Geo Hahn]

The parts came from Radio Shack:

I modified the inline fuse leads to have male & female quick-connects:

I then removed the Brown (hot) lead from the relay and put the fuse inline with it:

I suppose it could also have been put inline with the Yellow/Purple lead to the solenoid.

 

[BillyB62]

After a really nice time at the Portsmouth car show in RI, I came home and connected a 16 gauge wire directly from the battery to the yellow/purple wire under the dash and heard nothing. I then climbed under the car and attached the wire directly to the wire hanging out the solenoid - again nothing. Not wanting to believe a new solenoid was bad out of the box, I broke out my test light to make sure I had continuity through the wire, I did. Touching the wire to the solenoid wire, I could see mini sparks, but no sound from the solenoid itself. While under the car, I noticed the wire coming out of the solenoid had what appears to be a shrink wrapped connection on it I hadn't noticed before, making me think the solenoid might not have been brand new after all. I'll buy a new solenoid tonight.

Thanks to all for your help....like I said I doubt I would've gone down this path with what I thought was a new solenoid.

 

[Geo Hahn]

It has been almost 10 years since I even looked at my OD - but I think you can manually engage it by flipping a lever on the right hand side - sort of manually doing the work of the solenoid.

If so, you might want to try that to confirm that there isn't something binding. Hate to have you go to the expense and bother of replacing the solenoid if the problem is mechanical.

 

[BillyB62]

As recommended by Geo & Randall in previous threads, I've also added the 8amp slow blow fuse (on fuse block 2). I'd also like to mention that Randall recommended adding a diode to C2 (or 87) to help absorb the inductive kickback to help preserve the relay. This is something I'll also do. Here is the link to the previous thread:

https://www.britishcarforum.com/bcf/showthread.php?93931-TR3A-Overdrive-Wiring-Harness-Installation