1989 240DL No ign. lights except overdrive arrow on start

[coswood]

1989 240 DL electrical anomoly with overdrive

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I have a 1989 240 DL wagon which exhibits the following problems:
When the key is turned to ON, only the yellow overdrive arrow light comes on the instrument panel. Pushing the OD button on the automatic transmission does cycle the light on and off. NONE of the normal engine oil, battery, or other lights come on. The bulbs check good with an ohmmeter. The car will start and run, but none of the gages register (speedo, fuel, temp, etc.); but the alternator does NOT put out any charge. I had the alternator tested at a local NAPA auto parts store; they advised replacement- which I did. It made NO DIFFERENCE. After driving it for approx. 15-20 minutes, the red BATT light comes on- and weakly flashes. Coincident with that, the speedo, fuel, and temp gages show some readout- but not a correct/ normal indication. The car wil shift in and out of overdrive- but the yellow arrow is ON when it is in overdrive (4th), and OFF when it is in 3rd- just the OPPOSITE of normal! What the hell is going on here?

[93Regina]

What the hell is going on here?

My 1993 acts up once in a while, and has a similar situation, but speedo registers about 1/2 speed.

I've never got serious about it, cause it don't get serious. But, from ignition switch, there is a power wire that feeds the battery charge light, and it feeds other items in instrument cluster. From ignition switch, it could be a Red/Black wire (schematic shows Blue wire also, but???)

Might remove OD Relay and see what happens. If no change, see if you can find the Red/Black wire at ignition switch, and feed it power. But, try to trace out this Red/Black wire first to see where it goes; you might have to remove cluster.

Looking at schematics, I'm puzzled. My hunch is there is a break in the instrument-cluster's ribbon power strip (if it has one) or its feed wire or feed plug, something wrong with Red/Black wire's power at ignition switch, and because of this loss of power, the OD relay is back-feeding current to OD light.

At ignition switch, this same Red/Black wire feeds to the ECM on pin 35, which powers up some modules; this would suggest its getting power from ignition switch.

I'd have to pull plug at ignition switch and examine it, which I have not done yet. I'm not sure here, but I think on my 1993, the alternator will charge when a specific RPM is reached.

On the diagnostic connector, there is a Red/Black wire. If voltage is here, then Key Switch is working OK. This Red/Black wire feeds ignition system also, which if engine is running, then the key switch is providing power to both ECM and Ignition computer. So, problem points to instrument cluster's power feed in some way.

[93Regina]

If your speedo is not working, this suggests the feed-bus on instrument cluster is not getting power.

[Velvetjessu]

I know this is a few years old, but I have the same exact problem on my 240DL. We had the overdrive relay replaced, but he problem persists. Did you ever find a solution? My car is at the mechanic now and I’d be so grateful for any advice.

[93Regina]

... the overdrive relay replaced...

I was going to replace the ignition switch, which requires several hours, but I let this slide. I suspect its the postive feed wire going to instrument panel, or something in instrument panel.

I was going to put a jumper wire on the postive feed wire to instrument panel, at ignition switch, but I decided not to splice it.

Problem is, it works fine, and then it doesn't...

When not working, I make sure engine revs past 2,200 RPM, so the alternator "powers up." Hence, I know nothing enough postive juice is flowing to alternator's idiot circuit (power via light bulb in instrument panel). Once I kick up RPM, iirc, the idiot light will go brighter.

I drive via tach I installed, so I have a relative idea of my speed...most of my miles driven are rural, with about zero LEOs checking speeds.

Thus, either postive feed wire, ignition switch, or instrument panel...if it ain't broke, you can't really fix it. You can throw parts at it

[Velvetjessu]

Thanks so much for the response. I just bought the car a few weeks ago and love it, but I’m not mechanically or electronically savvy. My mechanic is advising me to try and find a new instrument cluster circuit board.
It’s so interesting to me that we’re having the identical issue. Right now everything’s working fine, it comes and goes. I feel like it’s related to the ignition, because after I turn the key whichever it decides to do is how it stays. It doesn’t fluctuate while the car’s on. David from Wagonmeister suspects the switch block on the back of ignition key unit may be bad, so I may look into that. It sounds like that’s the direction you’re leaning as well.

[plymsat71]

Googling my recent situation led me to this forum/thread. Exactly the same issue discussed above arose after my 245 sat for about a week while I was on vacation. Prior to that week the wagon performed flawlessly without any similar problems. It's charged up and the battery is strong but something is glitching, big time. I wonder if in the years that have passed since the last message if anyone solved this tricky issue. Thanks!

[reeltapegone]

Pull the cluster and in the top center of the rear of the printed circuit board is a connection via two points. It is a thin line of copper PCB along the top of the speedo ( I think but my memory is poor but you will see it ) .Get out your VOM and check continuity between those two points. You will find it open. An easy fix is just run a jumper wire between the two poles. The diodes in the alternator will not excite without this connection and you will have no charging system function as it is connected to the chg. system lamp. Fixed quite a few with this same issue.