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Discussion Starter · #1 ·
I have a 1997 thunderbird with the 4.6 engine. recently the speedometer stopped working as did the odometer, all other gauges work fine. I'm totally baffled on what it could be. I had a mechanic look at it and he hooked up his computer and it showed that the speedometer is sending the signal to show vehicle speed.

any help would be greatly appreciated

thanks,
Matt

also I don't know if this is in the right section or not, I'm new here so I don't know my way around yet
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I would take the front clear plastic cover off the cluster and re-seat the entire speedo section of the cluster as well as both cluster harness connectors. There's 25 years of age on the electrical contacts and there's probably some corrosion.

When you work to get the cluster bezel out, drop the steering column so you don't have to flex it to clear the steering wheel. The 97 cluster bezels are unique to that year and are unobtainium these days if you crack it.
 

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Discussion Starter · #3 ·
I would take the front clear plastic cover off the cluster and re-seat the entire speedo section of the cluster as well as both cluster harness connectors. There's 25 years of age on the electrical contacts and there's probably some corrosion.

When you work to get the cluster bezel out, drop the steering column so you don't have to flex it to clear the steering wheel. The 97 cluster bezels are unique to that year and are unobtainium these days if you crack it.
thank you for your reply. I had a mechanic look at it, he took it out and checked the wires and connections and he didn't quite know and was suggesting a new pcm. I'm hoping that there would be a common issue that would cause it.
 

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1994 Cougar XR7 DOHC/5-Speed
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thank you for your reply. I had a mechanic look at it, he took it out and checked the wires and connections and he didn't quite know and was suggesting a new pcm. I'm hoping that there would be a common issue that would cause it.
It’s not the PCM, the speedometer isn’t tied to the PCM in these, the speedometer/odometer gets its input directly from the sensor.

Does cruise control work?
 

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Discussion Starter · #5 ·
It’s not the PCM, the speedometer isn’t tied to the PCM in these, the speedometer/odometer gets its input directly from the sensor.

Does cruise control work?
Cruise control does not work. I just noticed yesterday that the cigarette lighter keeps blowing the fuse too.

thank you for replying
 

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changed the VSS and the problem is still there. IDK what else to do
Query your ECU and see if IT sees the VSS signal (it shows a speed reading).

If so, we've eliminated the VSS and the wiring into the greenhouse area; it'll be time to check the wiring behind the instrument cluster.

If not, then we need to check the wiring from the VSS to the splice or the ECU.

Simple quick test.

RwP
 

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If the eec doesn't see it, it doesn't shift gears at the right spots; it's easy to check.
 
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If you slow down at a redlight slowly, it shoulddownshift as well .
 

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And if it's doing that, then the VSS is doing its job.

So time to chase the wiring. Remember, it COULD even be a folded finger on the flex PCB on the back of the cluster ...
 
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1994 Cougar XR7 DOHC/5-Speed
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If cruise isn't working due to a lack of VSS signal it's highly unlikely the origin of the problem is a contact on the instrument cluster, at the very least it's got to be a fault before or in the secondary junction box where the signal gets split from the source and distributed. I'd start probing circuits for continuity and shorts at this stage
 

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if the downshifts happened, it's at least getting to the eec; that at least means the fault is where it goes from the eec to yhe dash, so it's at least not under the car.
I do think dropping the tranny is easier than pulling the dash...
 

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If cruise isn't working due to a lack of VSS signal it's highly unlikely the origin of the problem is a contact on the instrument cluster, at the very least it's got to be a fault before or in the secondary junction box where the signal gets split from the source and distributed. I'd start probing circuits for continuity and shorts at this stage
But, the cruise can have another problem.

Hence why I'd look for the VSS going into the ECU (and if it's there, then the cruise has the VSS signal!); and I'd not worry about cruise until speedo was working.

(Cruise can also be a bad cruise control switch not working, or a bad vacuum line, or any of a number of other items. So it's secondary; worry about the speedo, and then see if cruise comes back.)

Also why I say "If it's OBDII, datalog the speedo into the ECU and see what's happening". Does an automatic probe of the signal TO the ECU; if it's failed, then you've got a problem before the splice (for a 1997, according to the EVTM, that'd be the secondary junction block, for instance. EVTM page 31-2.)

If the ECU has a signal, but the speedo doesn't, it's somewhere between pin 12 of the secondary junction block (where the VSS signal goes in), and either pin 7 of the SJB, or the connection at the cluster.

Cruise control comes off pin 11 of the SJB. So I'd also check there.

But once again, the speedo feeds the ECU off pin 6 of the SJB (again, specifically for a 1997; other years, well, they may be different. Don't THINK so, but can't be arsed to check right now.)

Or, you know, start probing like crazy and hope we hit the problem ;)

RwP
 

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But, the cruise can have another problem.

Hence why I'd look for the VSS going into the ECU (and if it's there, then the cruise has the VSS signal!); and I'd not worry about cruise until speedo was working.

(Cruise can also be a bad cruise control switch not working, or a bad vacuum line, or any of a number of other items. So it's secondary; worry about the speedo, and then see if cruise comes back.)

Also why I say "If it's OBDII, datalog the speedo into the ECU and see what's happening". Does an automatic probe of the signal TO the ECU; if it's failed, then you've got a problem before the splice (for a 1997, according to the EVTM, that'd be the secondary junction block, for instance. EVTM page 31-2.)

If the ECU has a signal, but the speedo doesn't, it's somewhere between pin 12 of the secondary junction block (where the VSS signal goes in), and either pin 7 of the SJB, or the connection at the cluster.

Cruise control comes off pin 11 of the SJB. So I'd also check there.

But once again, the speedo feeds the ECU off pin 6 of the SJB (again, specifically for a 1997; other years, well, they may be different. Don't THINK so, but can't be arsed to check right now.)

Or, you know, start probing like crazy and hope we hit the problem ;)

RwP
97s don’t use vacuum servo cruise systems, there’s really not much that can go wrong with the electronic ones and it seems like a strong coincidence to me there would be TWO things wrong with it at the same time. Hey, I’m trying to save the OP the possible destruction of a hard to find 97 cluster bezel chasing a bad connection that I am confident isn’t the case.

The secondary junction block isn’t hard to access to probe, you need to crawl under the dash but nothing needs to be removed to get to it, it’s out in the open above the trans tunnel
 

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nods

Hence my suggestion to see if the ECU is seeing the VSS signal or not, by whether it picks up the road speed, or not.

RwP
 
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