• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR2/3/3A Calling all Wiring experts TR3 Overdrive Wiring ver A or ver B or are they the same?

Share this page

luke44

luke44

Jedi Warrior
Country flag
Offline
I got my trans back from Quantum but when I went to wire up the OD I found in my records from 10 years ago a suggested wiring layout from TRF entitled “from 18913”. My car has the original screw on connectors and was wired per the TRF option 1 below which matched up with my subharness from British Wiring. but I also see option 2 which I posted years ago is different.

Do these 2 variations amount to the same thing? I’m assuming the TRF version has power to the switch which then switches the relay on at W1, sending power to the trans switches via W2.

FullSizeRender.jpeg


This is the one more commonly seen but my old records seem to indicate TRF indicated a change at s/n 18913?

IMG_0137.jpeg
 
Last edited:
Both will work, it is just the first way the switch is before the relay, the second is after the relay,
The second option will put less stress on the switch, as the current is going through the relay first which acts as a resister.
I think the second way of doing it will prolong the life of the switch which is probably why it was done this way
 
Nice to have it confirmed, I’ve never taken a relay apart so wasn’t sure if W1 connected to W2. As I think back almost 10 years ago now, the sub harness may have come from TRF which led to the sketch above, can’t recall.

The sub harness wires are exactly as shown in the #2 TRF example, so for those come later it’s a reference to match up the wiring method with the harness you have. That’s possibly variable based on source/supplier.
 
While you’re working on it…Randall always recommended using a diode on the solenoid side of the relay, to reduce the high voltage spike across the relay contacts. That’s the main way to increase the relay life.
 
Thanks John, yes I saw that while researching the various posts. Debating whether to incorporate one while I wait for my 90 angle adapter to come in; I broke mine putting the trans cover on. :ROFLMAO:
 
I recently installed a TR6 OD trans in my 59 TR3A. There was no need for a 90 degree angle drive. I just used the longer trans cable made for the OD units.
I did follow Randall suggestion regarding the diode. I also added a fuse where he suggested.
I also added a small indicator light on the dash to show when power is sent to the solenoid/ tranny is in OD.
Charley
 
If you do use the 90 degree angle drive watch for the added washer that should be added. I installed the longer cable on my OD so I did not need the angled drive.

David
 
Back
Top