2nd Gen Non-Engine/Transmission Overdrive Switch & Bulbs

[biggy238]

Well, at 272K miles, both of the bulbs in my overdrive switch have bit the dust.



I poked around with my multi-meter until I found the circuit for the headlight illum for the switch (that bulb is still shot.



What I did manage to do was put a 12V red LED in the place of the OD off Bulb. Even had it working for a while, but the truck would never lock the clutch in the torque converter.



What I decided to do, was to find out what current needed to pass through the circuit to function normally. I cranked the meter over on Amps and found a suitable ground. I touched the red lead to pin 3 (orange wire/white tracer)and got something for a second or so, and then it flat lined. I thought that I had juiced the multimeter so I popped the fuse out of it and checked it. IT's fine.



The question is, what have I done to the circuit? I put the switch back in and the LED no longer works. I didn't get to run the truck far enough to see if it still tops out in third gear.



I'm going to be ****** if I zapped the pcm.



PS I know about the shift lever mod. . I don't want it. I like my switch, i'm so used to it I still smack it to set OD off even with its not working. Not the lever would help it at this point.

 

[biggy238]

Well, I figured out that I didn't have lockup because my TPS/POT was cranked way up, denying me lockup.



I still need help on how to get my OD off circuit back

 

[DBraunig]

This is the best i can do for you brother, I hope it helps, let me know if you need more wiring diagrams.



Dave



OVERDRIVE SWITCH

Automatic transmission equipped vehicles may have an overdrive switch. The operator disables or enables overdrive when the switch is depressed.



The overdrive system consists of a switch connected to the Powertrain Control Module (PCM) and an overdrive ON/OFF indicator lamp.



If overdrive is currently enabled, it is disabled when the operator depresses the overdrive switch. Also, if the operator already disabled overdrive, it is enabled when the switch is depressed.



Circuit T6 from the overdrive switch connects to cavity C13 of the PCM and provides the overdrive signal. Circuit Z1 provides ground for the switch.



In the START and RUN position, the ignition switch connects circuit A1 from fuse 3 in the Power Distribution Center (PDC) with circuit A21. Circuit A21 connects to the bus bar in the fuse block that powers circuit F12 through fuse 11. Circuit F12 supplies power for the overdrive ON/OFF indicator lamp. The PCM turns the overdrive ON/OFF indicator lamp ON or OFF by providing a ground for the lamp on circuit T18.

 

[biggy238]

Don't listen to what they tell you... . You're a beautiful, beautiful man David Braunig

 

[biggy238]

O. k..... I popped a fuse. . the one above... . It's labelled buzzer control.





In case anyone else is interested in this, I have replaced the bulb in the dash mounted overdrive switch with an LED. My first attempt, I used a pre rated 12V 1. 5 milli-candel (the measurement for luminous output)

RED LED. It sucked. I also thought that the LED was carrying the signal for the PCM. It does not. I had the potentiometer that replaced my TPS all screwed up, so I was never getting converter lockup.



Anyway, I pulled the switch back apart and took out the red LED and replaced it with a white light 1100 milli-candel 3. 6V LED, PN 276-320 from Radioshack. Obviously a 3. 6 volt LED won't live well being fed 12V, so i soldered in a 680 ohm resistor to the input side of the LED, thus dropping the voltage sufficiently. It works perfectly. .



Also, there is residual voltage on the circuit even without the OD switch engaged. It acts almost like having the night illum on for the switch, which is nifty because I broke the other bulb off of the switch.



If any of you want to try this, PIN 5 is the PCM switched ground and PIN 3 is the V+ (source voltage) These pins are numbered if you look at the backside of the switch. I also bought some 7000 mili candel LEDs but I thought they were overkill, and from the looks of the 1100 they would have been.