Hello,

I have an '85 car that had a good 4+3 in it which I pulled off to transplant into another 85. However, once I pulled the bad one off the other car and looked at it, the two trans have different plugs on it, and the good one is missing a TV cable input as well. I installed the good one with no TV cable onto the other car and now the overdrive does not work, I'm assuming whatever plug is missing on the harness controls the overdrive. My question is, is the 4+3 without the TV cable an 86 or different model year? In order to run that trans on the 85 car, do I need to do an ECU swap and wiring harness swap as well?

The good trans (with no TV cable) has 3 large weatherproof plugs with clips, while the other one (with a TV cable) only has 2 large plugs, with the plug under the 2nd shift lever blocked off. Can someone provide me with some information as to the differences between the two and what each plug does?

 

There is only 1 connection that directly controls the OD on the 4+3s. The other connections are attached to the manual part of the tramsmission. Those switches tell the computer what gear youre in. The TV was eliminated in later years. Im not sure which year they went away but i think it was 87. As i understand it, the TV cable is simlly there to disable the OD when you punch the throttle. In the later years, the computer uses the TPS to determine that. If it were me, rather than worry with trying to make it work, id run a switched wire with +12 volts on it down to the input to the OD and just turn the OD on and off manually.

 

The plugs on the D.N. trans are only mechanical switches, logic for the OD and the Speedo and backup lamps connectors.

.My '87 has only the one switch on first gear, see the photo below

The '87 does have a Ist gear switch, this prevents Ist gear OD engagement.

But since the ATF pressure is from a pump, within the DN Overdrive unit, that is turned by the drive line. Hydraulic pressure to engage the OD can't be reached until a particular speed.

But if you bypass the OD switching on your C4 do know if you forget to turn off the OD when you come to a stop, when your car reaches the speed at which the OD engages,,, It Will Be Harsh and could damage the OD.

You should be able to Swap the D.N Side Covers and utilize the 3 switches with NO mod's to your wiring.

If your interesting in seeing the inside of the OD unit there's an excellent video on YouTube

Here's a few photos of '87 DN transmissions.

Good Luck,,,, Michael

this is a '87 DN, note a Ist gear switch on the side cover plate. The Reverse switch (brown connector)for the back-up lights can also be seen


This is a '87 OD unit


This is a side view of a '87 DN with the OD. It's been several decades since I puled an early C4 DN, so I can't tell you much about the early DN trans other than the side covers which are steel should be able to be swapped.


This is the '87 DN that pulled last year to install a new clutch kit and flywheel in my '87 Convertible. You should notice there's little differences from the early years.