Speedometer issues...best course of action?

[sjwelds]

Hey all.

On my truck the speedometer (speedo for short -not the underwear-) has been dying. So what happens is start truck and nothing. just speedo dead. all other gauges fully functional. rap dash sharply above instrument cluster and she comes back to life. Well, it's becoming increasingly difficult (read: more sharp raps, less success at revival of speedo) to get the thing up and going.

Now, I understand that the power source for the speedometer is some sort of flapper type deal that makes connection when you install the instrument cluster?? Educate me on that...

Also, is there options and opinions on aftermarket speedometers?

Tired of a sore hand from sharply rapping the dash....

Thanks for reading

 

[BDCarrillo]

The factory OBS connector is a plug that locks into the plastic gauge cluster. No flapper type deals here!

It's pretty easy to get the whole cluster out... Pop trim out on either side of wheel, remove torx screws. Pull headlight knob out, and stick a flathead in the slot to release it. Tilt wheel down and put in 1, then pull cluster trim loose. Disconnect FSV and warning lamps. Remove trim fully. Remove 4x torx screws on corners of cluster and pull loose. Disconnect 3x plugs and you're home free

Speedo is black plug in the middle.

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Note the four pins passing through the circuit board, in the center. If those get loose, the gauge may act up.

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Not sure of any way to bench test it, unfortunately... Maybe put the rear end up in the air and run it in gear

 

[madpogue]

Does the odometer go blank when the speedo drops to zero? If not, does the number remain the same (not counting up) during the time the speedo is inop?

Automatic or manual transmission? If automatic, is the shifting affected when the speedo is inop?

 

[sjwelds]

Yes odometer goes blank. Looks like they breathe the same air.

Fortunately, manual trans. Doubt it'd be vss issues anyhow, as it's either working, or dead in the water. No in between

 

[IDIoit]

dont force it. get a bigger hammer!

 

[madpogue]

Yes odometer goes blank. Looks like they breathe the same air.

Main power to the PSOM, then, or poss. even that fuse. Indeed, same power for both, and the VSS signal drives both. But if it were the VSS signal, the speedo would drop to zero, but the odometer would still display the number (power), just not counting up (signal).

 

[sjwelds]

Yeah ok but why does rapping on the dash cause things to come back alive? To me that points to an issue with the connection at the instrument cluster

 

[sjwelds]

The factory OBS connector is a plug that locks into the plastic gauge cluster. No flapper type deals here!

It's pretty easy to get the whole cluster out... Pop trim out on either side of wheel, remove torx screws. Pull headlight knob out, and stick a flathead in the slot to release it. Tilt wheel down and put in 1, then pull cluster trim loose. Disconnect FSV and warning lamps. Remove trim fully. Remove 4x torx screws on corners of cluster and pull loose. Disconnect 3x plugs and you're home free

Speedo is black plug in the middle.

You must be registered for see images attach

You must be registered for see images attach

Note the four pins passing through the circuit board, in the center. If those get loose, the gauge may act up.

You must be registered for see images attach

Not sure of any way to bench test it, unfortunately... Maybe put the rear end up in the air and run it in gear

OK so in your second pic...What are the two openings that look like a flexible type of connection? Does that have anything to do with my problem? Looks like those things wouldn't be just the most reliable way to transfer current/signal....

Edit..so is that where two of the plugs on your first pic connect?

 

[madpogue]

The interior fuse box is in the dash (that you're rapping on) as well. I don't remember offhand if the fuse that energizes the PSOM energizes anything else, but that's in the owner's manual. You might want to check that, and if anything else is on that fuse, see if that acts up at the same time as the speedo/odo.

Those connectors on the flexible circuit board of the cluster are where the harness connectors (first photo) for the rest of the cluster connect. That's how instrument cluster connectors have been designed for close to 40 years (my wife's '78 Omni had the same design). In any event, the PSOM has its own connector, which is the black connector in the middle of that same photo.

 

[sjwelds]

Thanks. So I don't have an owners manual for this truck. Anyone know off-hand what fuse and where?

 

[sjwelds]

Well, nothing like posting about the problem to make the problem disappear. Drove it yesterday and today and works perfectly.

'Course, now that I posted this, it'll go back to its old tricks, no doubt

 

[sjwelds]

Bump. Still haven't figured this one out. The problem seems to be getting worse. I have a harder time getting the thing to work. I did check the fuse that powers the speedometer ( at least, according to the fuse box cover) and it was good. What are the next places I should be checking?

Be gentle. I SUCK at wiring and anything electrical.

92 7.3 ZF5 F350 4X4 for those who can't see my sig, if any.

 

[crash-harris]

Pull the cluster loose from the dash and make sure the harness is locked in place. When if they are, I'd spray both sides of the connectors down with electronics cleaner.

 

[madpogue]

^^^^^^ +1; and the same goes for the fuse. Even if it looks good, make sure it TESTS good. Even if it tests good, check that it's _tight_ in its socket. I've seen more than one fuse create a flaky connection when the socket terminals don't grab the blades of the fuse tightly. I've even "cheated" sometimes and twisted the blades a bit with a pliers, just to get the to grab tighter when you push the fuse into the socket.

 

[sjwelds]

Thanks again guys. Guess it's time to get down and dirty with the instrument cluster. The fuse does fit really snug in the fuse holder, and anyway, the intermittent nature of the issue makes me think something other than fuse.

Wish me luck. With my record I'll break something at the very least