Need some electrical pros' input.

[Eaglefreek]

Bear with my explanation,I'm just a hobbyist and have very minimal electrical knowledge. I'm am going to be installing an AW4 transmission from a Jeep Cherokee into my AMC Eagle to gain overdrive. It is an electronically controlled transmission. I have all the wiring figured out, it's rather simple actually, but I have one mod I want to make. The one downfall of the AW4 is that you can't select first and second gear independently. The gear selector has one location for first and second and the TCU, transmission control unit, decides what gear to put it in based on output shaft RPM and the throttle position sensor. There are two solenoids that are involved with first and second gear. Solenoid 1 is on and solenoid 2 is off for first gear. Solenoid 1 is on and solenoid 2 is on for second gear. Others have used 2 toggle switches to either de-energize or energize solenoid 2 depending on which gear they want to be in. I want to use one switch. In my wonderful drawing below is a three position rocker switch. In up position, power will be taken away from solenoid 2 to keep the transmission in first gear. In the down position, 12vdc will be supplied to solenoid 2 to keep it in second gear. In the middle position it would run as designed allowing the TCU to energize solenoid 2 when it wants to via the jumper with a diode. Am I on the right track? Don't have a clue? Is there another switch that will allow me to do this easier? What type of diode for the jumper and should I have a diode on the relay between 85 and 86? Does there need to be a load on 87 when the relay is open? THANKS! Here's an article with using two toggle switches. http://www.fourwheeler.com/techarti...4_jeep_cherokees_transmission_lock/index.html

 

[dwh]

So...

Switch Up: Power is cut to Solenoid 2 and the tranny stays in 1st.

External power from ign is supplied to terminal 86 on the Bosch relay. This energizes the coil, causing 30 to be connected to 87, which goes nowhere.
Power from TCU to Solenoid 2 is cut.
Tranny stays in 1st.
Okay so far.



Switch Down: Constant power is supplied to Solenoid 2 and the tranny stays in 2nd (assuming of course, that the gear selector is in 1st/2nd).

External power from ign is sent directly to Solenoid 2, with backfeed to TCU prevented by diode.
Tranny stays in 2nd.
Okay so far.


Switch Center: Normal operation.

Switch is 'Center OFF'.
No external power is suppled to 86 on the relay, so 30 is connected to 87a, which connects the TCU to Solenoid 2.
Solenoid 2 is controlled by TCU.
Normal operation.
Okay so far.


Yea, that would work.

But there is no need for a double pole switch, you could do the same with a a 'single pole, double throw, center off' switch and just running the line from 87a through the diode directly to Solenoid 2. I can see that the extra terminals on the double pole switch might be a convenient place to make connections though.


You could also rig an idiot light from the top terminal on the switch (top left in your diagram - same terminal that feeds to 86 on the relay) so you'd know you were 'Locked in 1st'.

Rigging an idiot light for 'Locked in 2nd' would be a little trickier since you probably wouldn't want it going on and off as the TCU hots up Sol2 in normal operation.

You could do that easily though by running from 87a though the diode and then directly to Sol2 (switch lower left terminal).
I.e., NOT connecting the TCU to the unused right switch center terminal.

Then, you could jumper from switch center left to switch center right, and connect the 'Locked in 2nd' idiot light to switch bottom right.
So, when the switch is in the down position Sol2 and the idiot light are both constant hot.

EDIT: Or, by running from 87a directly to Sol2 though the diode, you could jump from switch left center to switch right center, and just use the right side top and bottom connections to feed the idiot lights.


As for the diode. Dunno...I'm not an electronics guru. I would assume the diode specced in that article you linked would work.

 

[dwh]

Revised with idiot lights:

 

[Eaglefreek]

Awesome, thanks! I wish I thought that clear when I had the flu. I like your idea with the idiot lights, cause I've been accused of being one a few times. :ylsmoke: