1991 Dodge Ram 50 2.4L not going into overdrive


Old 04-13-14, 04:52 PM
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Join Date: Apr 2014
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1991 Dodge Ram 50 2.4L not going into overdrive

Hey folks, by way of introduction, let me fill you in on some history: My son is 16, passed his license test with flying colors, and has purchased a "beater truck he can learn to repair" (his words) for $650. The sign on the truck said "Needs work" and it does. I have other questions to ask later, but one at a time. First up:

The overdrive does not come on at freeway speeds, or any speed at all. Stays in 3rd all the way up to 60 mph, at which point we decided to stay off the freeway and take the 40 mph backroads until we fixed the overdrive. Lots of loose/additional wiring under the console, most of it for the previous owner's stereo 'experiments' but we found that from the overdrive switch there are 3 wires, red, black, and yellow. They terminate at a plug, which only had a red and yellow wire attached to the other side. The red wire had been cut and a wire spliced from the switch side to a screw in the body. On intuition, we removed that spliced wire, reconnected the red wires at the cut, and jimmied a black wire where there was space for it in the other side of the plug and attached that to ground. No difference. We then tested the switch by disconnecting the plug and testing continuity with a multi-meter. We got continuity between the red and black wires with the switch on, but nothing between the yellow wire and either red or black with the switch on or off.
Today we are attempting to remove the switch to see if the yellow wire is disconnected or the switch is faulty, and the one trouble we are running into is there is no mention anywhere of the overdrive circuit in the Chilton manual we bought. I have long used Chiltons for many impromptu repair jobs and found them adequate, but this time it was no help. Nothing on the internet either, so I stopped in here.

My questions: if the switch is good, where do the wires lead to after they leave the steering column area, what else can we look for, and when do we call it quits and just take it in for a transmission job (which I would like to AVOID)?

EDIT: The switch appears to be working now, with the circuit appearing to be SPDT with the red wire as center: Y-R-B
So when the switch is on, Red and Black are connected, and when off, Red and Yellow are connected. I found in the Chilton's manual a reference to an overdrive solenoid, which I assume this switch controls, but NO wiring diagram to tell me where and what to test for. Anybody know?

Last edited by edvard; 04-13-14 at 05:55 PM.
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Old 04-22-14, 08:19 PM
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Join Date: Apr 2014
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Finally got a proper OEM repair manual, and got the wiring straightened out; it really is just the red and yellow wires, the black wire from the switch to the coupling is a dummy. Still no overdrive. I've read everything I can find on getting to the overdrive/lockup solenoid but still a bit fuzzy. I guess we won't know until we open the tranny up and take a peek inside. Is there any way to test from the electrical connection if the solenoid is bad?
Old 04-24-14, 06:12 AM
Join Date: Apr 2014
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I couldn't find much on the Internet about this either. A lot of vague info and little else.

Meanwhile, it does appear that some of these OD systems used a certain sequence of button pushing in order to engage/disengage the OD and/or "towing gear" options. Not sure if this is the case with your son's particular truck, but you might want to check the owner's manual (if you haven't already).

I also noticed that OD solenoid failures seem to be common to these, or similar, vehicles. Unfortunately, I've been unable to find any solenoid troubleshooter flow charts or test procedures for this truck. And nor could I find any info on replacing said solenoid...

As for Chilton, I too found them to be "adequate" back in the '70s '80s. However, I recently bought a used Chilton manual for a '93 Caravan only to be disappointed with it's lack of certain, yet important, repair info.

Good luck, and welcome to the doityourself forums!
Old 04-25-14, 03:51 AM
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Not sure if this will help but GM in the 80's used a manifold vacuum swich connected in series with the OD solenoid which was located in the transmission.
The idea behind the vacuum switch was that when you pressed on the gas hard while in OD the manifold pressure would drop to take the transmission out of OD.

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