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Wiring and speedometer issues, Update

1312 Views 72 Replies 7 Participants Last post by  ViolenceJack
Good morning gang. Since last time I was here my D250 is running good. I do however have some problems still and cant find a clear cut answer online.

So my fuel gauge works, but when I start to move the truck it bounces HARD left to right. I know the gauge technically works because I added about 5 gallons of fuel to the tank and it went up. The dummy light for "low fuel" is on though.

The oil pressure(?) gauge is at zero and doesn't budge. The truck has oil.

I'm not 100% sure if the temp gauge works either, I haven't really let it run super long to get that hot. I did however put a new thermostat in because the old one was rusty and stuck shut.

The speedometer and odometer do not work either.

The dummy light for the parking brake and ABS both stay lit. I have messed with the connector by the e-brake and it appears to be intact, but when I move it by hand the dummy light gets a little dimmer.

My pawpaw had most of the dash apart and I really have no clue as to what all problems he was facing. He did have the red plug for the dummy light panel plugged into the gauge cluster, and the black gauge cluster plug just dangling. I'm gonna attach a couple pics of some plugs that I'm not sure about that were left unplugged with (seemingly) nowhere to plug into along with some loose wires just laying in the floor. And I have a picture of a little silver fella that gets HOT even when the truck isn't running. I have it unplugged because I don't want to walk outside to a burnt up truck. Also I am for some reason terrible at tracing wires. Its the one thing that absolutely overwhelms me.

Any help is appreciated.



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sorry to ping you @9297oldram but you helped me so much to get the truck running so I was wondering if you had any insight into the problems I have now? if not its fine
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The fuel tank module has a adjustable slide and the screws do come loose, you might want to check that because the module might not be sitting on the the bottom like it's supposed to.

Check your vacuum it should be around 25hg's.. there is a low vacuum switch behind the left hood hinge the rubber line could have fallen off.

That hot cylinder is the light around the ignition switch so you can see where the key goes in the dark.

Most will put aftermarket gauges in, a fuel presser gauge is a important troubleshooting gauge. 15 psi is all you need.
thanks for the response man. Is the only way to check the fuel tank module by dropping the tank?

And the vacuum line/switch is connected, however the big round brake booster (?) appears to be leaking a little. I just took the top off where you put brake fluid in and the back reservoir is full and the front is halfway full.

I guess if that little cylinder is only for the light at ignition switch ill leave it off, i dont forsee myself needing it.

And I was thinking about adding aftermarket mechanical fuel pressure and oil pressure gauges, but I would like to fix whatever is causing the issues on the stock ones as well.

Thanks for getting back with me
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The oil pressure sending units do go bad.

If your fuel tank is full i'd just jack up the bed drivers side, and loosen the passenger side bolts enough to allow movement to raise the drivers side and also disconnect the fill tube.
Ok I’ll probably go get a replacement oil pressure sending unit from napa today. Along with a mechanical oil pressure gauge.

And I won’t be able to jack up the bed today, all the bolts are rusted to hell.

You see in the first picture called IMG 925, in the floor beside that chain is a red and black wire connected to nothing. I just followed it and it goes straight through the fire wall to the battery. Any idea what it was supposed to connect to? Or any of these vacant plugs?
First thing that comes to mind is check the dash ground, and make sure the cluster is plugged in (those round pins get lightly corroded from sitting). Everything you describe indicates a dash ground issue...
Ok great info. Where are the dash grounds? Sorry i am still learning all about this stuff.
That red and black wire doesn't look Factory to me, looks like maybe CB wires or some other accessories he might have added.
Good call i think you’re right about that. There is so many unplugged plugs that i have no idea what they are for. the wiring on this thing is a nightmare
Update: Put a new oil pressure sending unit on, stock Oil pressure gauge works now thankfully. Next step is to get the speedometer and odometer to work, along with getting the Parking break light and abs light to turn off. I’m gonna attach a screenshot i took from another forum talking about similar issues to what i’m having and see if you think this could be my problem. Or perhaps the VSS maybe on the transmission? I haven’t messed with it at all yet or cleaned the connections so it could be that too
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The VSS assembly and wiring is the issue alot on these older Dodges. Also the sppedo gears are know to break in the dash cluster.
Ok great to hear. Once it stops raining here i’ll get out there and mess with the VSS first and see if it’s functioning or just dirty connections. I’ll update again with my next findings. Thanks again for all the advice oldram
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If it has the metal gearbox looking thing at the trans those can go bad.
Gotcha. And i can use the speedometer app on the iphone if absolutely necessary. I haven’t even drove past i’m guessing about 15-20mph just down my little dead end road just to test it. Brakes aren’t great so didn’t wanna go too fast. When I check out the VSS and clean up the area i’ll update you with my findings.
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Update: Just replaced the VSS today, Speedometer and Odometer still not functioning. And the temp sensor is still not working. All other gauges appear to be working correctly.

Also think there is probably a permanent flat spot on all the tires because when you get up to speed while going down the road it feels like riding on 4 flats even though they all have air.

I ordered a coolant temp sensor today from oreillys and realized it has to be the wrong one because it is tiny and the one on the truck has a big nut on it.

So i guess next step is to take the dash back apart and tear into the cluster to check the gears on the speedo and odo? Unless there is another speed sensor i’m unaware of on the 1990 d250
Is yours a mechanical cable or electronic with wires to the dash?
I think it’s electronic because there was only electrical connections connecting to the cluster from what i could tell. But don’t quote me on that. I’m not even sure what a mechanical cable would look like tbh.

and @Rug_Trucker what kind of damage could they cause?

Edit: It’s got the 3 speed transmission in it if that makes a difference
Trash and mangle your fenders, and inner fenders. Ever see a car tire explode? Steel belts tear the snot out of everything they touch.

I've blown car tires, and big truck tires.
Good to know. Told my wife today i’m not putting it back out on the road without new tires.
From my understanding, by the time the Cummins was introduced, the cable-driven clusters were not used. I believe they started phasing them in around 88, by 89 they were all electric.
Good to know. So either everything in the cluster has good power and ground besides the speedo and odometer, or the gears are fried in those. The process of replacing those doesn’t seem very fun. I’ve done it in a VW cabrio before and was hoping to never have to do it again haha.
Also to add, this is the new VSS i installed. It came with this new wire/connector, but i’m not sure exactly where it goes to. The old wire seems to go above the trans and I can’t see anything else from there. Do the stock one typically have this type of connection to remove the old wire and plug in a new one? If it’s just the wire going bad and i can put in this one it came with that would be great. Also of note, when I did take off the old VSS it seemed kinda rusty/oily where the shaft goes in. I’ve heard of the shaft hole rounding out before. Could potentially be another cause I reckon. I’ll have to try and figure out if that new wire is able to plug and play on mine when i get home today if no one knows if it will work.
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And last thing to add. I found this picture of apparently what it’s supposed to look like all connected. My VSS seems to be connected straight into the transmission without this ratio adapter part. Is the ratio adapter something that only goes on manual trans or something? Mine is the 3 speed auto.
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I crawled under the truck today for a bit to see if the wires for the VSS unplug from something. It seems it’s just wire all the way. So that makes me wonder, what is this plug on the pigtail from the new VSS supposed to plug into? If i can’t figure out why this speedo and odometer aren’t working this week then i’ll pull the cluster this weekend unfortunately. Gonna try the drill test on the new VSS sensor tomorrow to make sure that it’s not rounded out in the trans case.
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So my last post was about how my speedometer and odometer doesn't work. My brake light and ABS light are both on.

I have since put in a new VSS on the trans. That did not solve my problem. The new VSS came with a new pigtail connector so I looked at the old wires and copper was showing through on multiple spots so i cut em and put the new connector on with wire nuts. (temporary as a test) Still nothing to the speedo or odometer.

I was reading through a older post about how someone had the same exact issues as me and their fix was the ABS speed sensor on the rear axle pumpkin. So I got a new ABS speed sensor and installed it today. Lights are still on and the same problems persist. I went ahead and unplugged the box behind the glove box so I am only dealing with the brake light being on. Who needs ABS anyways.

Next step will be pulling the gauge cluster and looking at the speedo/odo gears which I have been putting off in hopes that there is an easier fix.So are there any other potential avenues to go down with these problems I'm describing before I tear into the dash again?
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Yeah I figured as much. I was really hoping that rear speed sensor replacement would fix my problems haha.
Yes it has 5 volts like it is supposed to. Oh and another thing that doesnt seem to work is windshield wipers. Not sure if thats relevant
You might try finding the ground wire for the VSS and ground it and see if the speedometer works.

The wipers could be a bad fusible link.
would the ground just be one of the 2 wires that go to the VSS?
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