I know this has happened to a lot of our trucks and I did an extensive search to try and troubleshoot my issues but came up empty. I have the dreaded gauge backing rot and decided to replace the whole mess because my speedometer just quit working as well.

I bought a complete unit with the newer plastic backing and all the gauges. It came with a printed circuit board as well. The numbers in the PCB on my old unit match the new unit. It is a D6TF106956.

The problem I ran into is when I plugged the PCB in and I tried the lights...I got nothing? I plugged the old unit in and tried the left blinker just for the hell of it and after wiggling the holder in the socket...I got it to light.

Is it possible the PCB is bad? It almost seems like it is a grounding issue with the new unit. I was under the impression that if the numbers match it was interchangeable...is that correct?

I am considering swapping out the old PCB on the new cluster, but I'm not sure if that needs to be done or I am missing something. Any help is always appreciated!!!!!

Edit: I doubt it's a ground issue because I did have the "Fasten Seat Belt" light illuminated when I turned the key on. Also, the oil pressure gauge was operable when the engine was started.

 

Did you also replace all the bulb holders & bulbs with new ones?? If not, they may be bad.On the holders, you can clean the contacts with fine sandpaper, & bend the contacts out so they make better contact with the PC. Clean the contacts inside the holder as well, I use a fingernail emery board, cut down to fit into the socket. You can replace the bulbs with new, or clean the contacts on them & they will usually work. I test each & every bulb to make sure they work, even new ones. Then I put them into the holder & test them again to make sure they work. Then I'll install them in the cluster.

That is where I would start.

 

I replaced ALL the bulbs with new ones...I figured it would be smart to do it now while the dash was out. I will try to clean the sockets and contacts when I get a chance. Its gonna snow pretty heavy tonight and plowing will take priority. Thanks for the reply...any other ideas???

 

Am I assuming correctly that if those D6TF numbers are the same the PCB's are compatible?? There are numbers that are stamped in ink that are different, but the ones molded in the PCB are the same?

 

The whole engineering number is the same? You've got the D6TF, then the ##### 'part number,' and then a suffix after that, which would be something like AA. That suffix shows if there have been any revisions to the design.

I wouldn't assume that they match. The best way would be to compare every trace from the wire harness out to all of the lights and gauges. I would probably try swapping out the IC PCB before comparing every circuit trace. They are not hard to R&R, the only difficult part might be disconnecting it from the Instrument Cluster Voltage Regulator - it kind of snaps onto the terminals like a 9 volt battery. You could always just swap over the ICVR along with the IC PCB, onto your new cluster backing. Ford used at least three or four different IC PCBs in the '79-'86 Mustangs, even though the basic gauge layout never changed during those years.

 

Please, when asking questions, list ALL the pertinent info, we are not mind readers. You failed to mention a single word of what you're working on: Year/model/engine/trans and etc.

You also typed an inaccurate ID number. No such thing as D6TF106956 .. The following is correct:

D6TZ-10K843-B .. Printed Circuit Board - Use with Oil/Amp GAUGES / Marked: D6TF-10C956-BA / Obsolete

1976/79 F100/350 / 1976/91 Econoline / 1978/79 Bronco.
-----------------------------------------------------------------
D6TZ-10K843-C .. Printed Circuit Board - Use with Oil/Amp WARNING LAMPS / Marked: D6TF-10C956-CA / Obsolete

1976/78 F100/350 & Econoline; 1978 Bronco.

 

Sorry it has been a long day after a foot of snow, but here goes. It is a 1979 XLT Lariat Ranger Super Cab. It was born with a 400 and a C6 with the NP205 transfer case. The numbers are identical on the back of both PCB's. I do not see any suffix that has been talked about on either. There is a 1 then the Ford script in the oval then SX and then the D6TF10C956. That's it...no suffix anywhere. The other thing I noticed that may be a problem is the speedometer in the original dash is 85MPH and the replacement one is a 100MPH. Is that going to be an issue?

Thanks for any help

 

The only other markings on the PCB are what look like they are stamped in some sort of ink. The old one has 6J1S20W and the new one has 6L922U. That is what it looks like...it is hard to read because of the age.

 

If it has Oil/Amp GAUGES, there is only one printed circuit board: D6TZ-10K843-B .. Marked: D6TF-10C956-BA

 

The speedo might be an issue. Some 100 MPH had the high beam light at the top of the speedo, like the 85 MPH. Other 100 MPH speedos had no high beam light at the top. If your 100 MPH speedo has the light at the top, it will work for you.

Trying to understand what you have.... Is this a new PC & plastic backer, with used gauges?? Or are the gauges new as well??

I doubt your PC is the problem, unless it is used & the contact points are corroded. Clean 'em all just to be sure.

Your best bet is to test everything in the "new" cluster. Test each & every bulb, then put the bulb in the socket & test it again. Clean the contacts on the sockets as I mentioned in my other reply. I use a battery charger & test leads with alligator clips, hooked to the contacts. When you have verified they work, then install them in the cluster. the gauges can be tested in the cluster. Use a 1.5V battery, & your test leads. connect a lead to each post on the gauge, the other ends to the battery. Watch the gauge, it should slowly rise to about 1/4 scale. If not, reverse polarity & try again. If the gauge doesn't rise, it is bad. The Alt gauge needs to be tested with an almost dead 1.5V battery. Even that low voltage will peg the gauge, reverse polarity & the gauge should swing the other way. Since you said your oil gauge worked, your IVR is good. If you feel ambitious, you can trace the bulb circuits to the plug socket on the PC & power them up thru the PC to test that way. I have a few different plugs cut off of the harness I use for this, it makes it easy. Once everything is tested, & confirmed good you can try the cluster in the truck.

I've refurbished probably 25 or so 73-79 clusters in the past couple of years. Testing each & every part each step of the way is what it takes to make these clusters work. Taking shortcuts always ends up costing a lot more time.

 

It was a takeout that was supposed to be good, but we all know how that works sometimes!!! I will do what you suggested and clean/test everything before trying to install. If I run into issues, would it be wise to swap PCB,s and keep the newer gauges and backing plate? What tricks do I need to know as far as taking the old one apart? I looked at the IVR, does that just snap off? I know I can MAKE it snap off, but I want to be able to use it again!!!

Thanks for all of the help...it is VERY MUCH APPRECIATED!!!!!

 

Well...after sanding contacts and testing sockets, I have lights in the dash again!!!

Thanks for all who gave some input in solving my problems with the "new" dash.!!!

 

Glad to hear you have them working!