Why 10.7 volt input at ‘71 Duster instrument panel?

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Ken71Twister

Ken71Twister

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I’ve been working on a number of items related to the instrument panel. When I started I noted that the voltage coming into the instrument panel was only 10.7 volts. I suspected dirty connectors and I’ve done a lot of work to clean connectors. I checked again today and it is still 10.7 volts. This is with the ignition switch on and car not running. Is something wrong or is this normal? Battery is fully charged.

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When you say with the ignition "on" you mean in the "run" position?

If you have a points distributer and the points are closed there is a good draw, look at the ammeter.

Try turning to accessory and checking again.

If it's the same then you will need to track down the bad connections.

That's a lot of voltage drop.
 
That is NOT normal Make REALLY certain you are on the correct pin, that is, that you are not reading it "backwards" or backside of plug vs front side--mirror image.

I would get right down to your ignition switch connector and check V at the "run" line and whatever else is coming out switched for "run" and "accessory."

Don't ignore the easy/ simple stuff. Make certain your tester is accurate, and make sure the other end is well grounded
 
Dana67Dart said:
When you say with the ignition "on" you mean in the "run" position?

If you have a points distributer and the points are closed there is a good draw, look at the ammeter.

Try turning to accessory and checking again.

If it's the same then you will need to track down the bad connections.

That's a lot of voltage drop.
Click to expand...
Totally agree with the points closed. Same with electronic takes around 4 amps when on and not running. You see if it is that way also at the battery?
 
The coil should not draw down that voltage. If it does, you have voltage drop AND THAT WILL AFFECT CHARGING VOLTAGE, the old saw, harness voltage drop

The main culprits are the big red ammeter wire through the firewall, the ammeter connections (rare), the igntion switch CONNECTOR, the switch, the dark blue IGN wire going back out the switch CONNECTOR, and of course the connector for the other end, in this case, the cluster/ board. ALSO on the cluster board make certain the pins are not loose, clean and solder if necessary

THIS GETS RIGHT BACK to my usual recommendation---if you have a stock harness with this problem, and don't want to got to a huge amount of work, then break the dark blue "run" wire coming out of the firewall. Use the firewall end to key a Bosch relay, feed the relay with a large wire, say, 14 or 12, fused/ breaker, from the big stud on the starter relay, and connect the engine end of the dark blue to the switched load contacts. THIS WILL USUALLY cure your over-voltage condition as well
 
Consider this... The starter gets its power through a large gauge wire with very little compenents and/or connections to lower the voltage to the starter. Everything else is supplied by a much smaller wire with a crowd of things in its path to degrade the current path. As soon as ignition switch goes to run position, some things begin drawing that voltage. So start at the beginning. Have a good 12 volts at both sides of bulkhead connector. With that you should have same 12 volts amp meter (across its shunt) and at every branch of black wires leaving a weld splice. One of those branches goes to ignition switch. See full 12 volts going into it the turn it to run to see what voltage loss happens at the blue and other wires coming away from that switch.
One thing to know about voltage paths and draws... There is a blue and a brown wire at ignition switch commonly known as start 1 and start 2. I can never recall which is which. Both connect to the ballast resistor. That resistor doesn't know or care which direction current flows through it. So with ignition switch in start position where on only one of the two should be hot, you will find lowered resistance voltage feeding back to the ignition switch on the other wire. Same in run position where only one should be hot in run, you will find resistance voltage feeding back to ignition switch on the other wire. This does not indicate a bad ignition switch. Many ignition switches have been replaced by owners who considered this back feed across ballast resistor to be a fault in ignition switch.
Factory service manuals with their wiring diagrams don't actually detail how current can travel connections to ballast resistor in both directions.
One more point to make, most instrument panels before 1972 had 2 of hot in run wires at their round harness connector. We know the blue one feeds nothing more than the gauge voltage limiter. The other (black maybe? I forget) feeds nothing more than the brake warning lamp in inst' panel and I forget where this wire originates. You might check voltage on that one also.
For 72 models they determined only 1 was required to power both features of the inst' panel so the blue one was omitted. Same wire that feeds brake warning lamp also feeds inst' voltage limiter via printed circuit board.
In my 67 model, I did add a relay mounted on the firewall to insure everything on the blue wire under the hood would get its full 12 volts without doing any diagnosis to prove the need for it.
 
All - I just reviewed inputs above and I’ll need to re-read a few times to totally understand all of the suggestions. Cutting to the chase - I got the voltage up some and reinstalled the instrument panel to check everything and take a short test drive. The fuel and temp gauges now work, blinkers are stronger, dash lights now working, and car starts and runs great.

I’m sure that I was on the right pin.

Ground is good and I’ve done a lot of connector cleaning. Did not go inside steering column to inspect/clean starter switch.

I used multiple meters and they agree on voltage data.

I do have points and, when I checked, the ammeter was substantially deflected with switch in run position. After disconnecting coil and alternator - much less ammeter deflection (still some) and voltage was up to 11.2 V. With charger on battery - voltage up to 12.3 V with run switch on.

The sad news is that my speedometer - tested for the first time yesterday after repair - is making a bad clicking noise and I’m going to have to pull everything back out and probably ship the instrument cluster back to shop that did the repair. At least it seems to correctly register speed but sounds like it will self-destruct if I continue to use it. (The speedometer shop told me - before sending the speedometer back - to inspect the new speedometer cable to make sure the center flex cable is in the correct position).

With the instrument panel out - I’ll have the (unwanted) opportunity to further pursue causes/fixes for the voltage drop at the cluster input pin. I can’t wait to go out in the Florida heat and pull the instrument panel out.

Thanks again for your help.
 
Be careful with the panel out, and be careful not to get down a rose paved crooked path.

Part of what I mean is, you may or may have disturbed a poor connection in moving things around, which may temporarily hide the problem,---or may it worse.

Also you are unhooking the ammeter itself which may be part of the problem (by removing the cluster)

"The usual" circuit for voltage drop is illustrated somewhat in the simplified diagram from MAD electrical concerning the ammeter.

Basically, ANY POINT in the path may cause drop. From the starter relay---fuse link-- through the FIREWALL CONNECTOR (large RED to ammeter)--through the ammeter--to the WELDED SPLICE, the LARGE BLACK to the ignition switch CONNECTOR, through the SWITCH, back out the switch CONNECTOR (now on the dark blue "run" wire, back out the FIREWALL CONNECTOR--and to the ignition system, the alternator field/ VR etc.

So in your case at the cluster, you can eliminate the last section back out into the engine bay, but everything else applies

ALSO REALIZE that EVERYTHING must be connected as normally as possible to test, because CURRENT through the circuit is WHAT DRIVES THE DROP


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Clicking in speedometer can be a couple of things... Cable applying pressure in any direction can move parts inside the head, especially where the tiny bronze bushings are worn. Another is the odometer spool. Either should result in a needle twitch or jump. When you get the panel out, lay it so the weight of the panel is against the input port/drive spindle of speedo. If the needle lifts more than 5 mph there is excess wear in the bushings. With the speedo out on the workbench, look closely at the drum shaped part for rub marks where one part is touching the other. If you can't find anything wrong with the head, check that the input port is/was properly cleaned. Route the drive cable to it a straight as possible.
 
Update on speedometer. With the cluster on a bench - I used a drill to run the speedometer up to mid 30s and there’s no clicking. I then jacked the back wheels off the ground and ran the car in 3rd gear and the disconnected cable made no noise. I reconnected the speedometer and ran the car in 3rd and the clicking noise came and went as I applied pressure to the plastic connector that clips to the speedometer. I’m thinking that my next step is to buy some lubricant and apply generously to the cable. I just read a suggestion that I use spray white lithium grease. Any other suggestions at this point?
 
Also - with the engine running - the voltage at the instrument cluster plug is over 13 V. I also found another pin for dash lights that reads 11.9 V with the engine running. Maybe I’m ok with the voltage issue. I didn’t run the engine earlier because I was in the garage and had a gas leak at the carb check valve that I’ve since fixed.
 
RedFish said:
Clicking in speedometer can be a couple of things... Cable applying pressure in any direction can move parts inside the head, especially where the tiny bronze bushings are worn. Another is the odometer spool. Either should result in a needle twitch or jump. When you get the panel out, lay it so the weight of the panel is against the input port/drive spindle of speedo. If the needle lifts more than 5 mph there is excess wear in the bushings. With the speedo out on the workbench, look closely at the drum shaped part for rub marks where one part is touching the other. If you can't find anything wrong with the head, check that the input port is/was properly cleaned. Route the drive cable to it a straight as possible.
Click to expand...
Your statement above makes me wonder if I may need to re-route the cable (if I can) to better align the cable with the speedometer head. Not much room in there to do anything. In the meantime - I’m going to get some lubricant.
 
I just read some threads regarding lubricant for the speedo cable and there are really some opposing opinions out there vs what to use. One comment I read makes me hesitate to put anything in the connector area vs risk of it getting into the speedometer itself. What lubricant do you recommend IF I add anything at all. The cable is new and I applied a thin layer of white marine wheel bearing grease to the cable when I installed it last month. I’m thinking now I need to focus on aligning the incoming cable to the speedometer head.
 
Ken71Twister said:
Also - with the engine running - the voltage at the instrument cluster plug is over 13 V. I also found another pin for dash lights that reads 11.9 V with the engine running. Maybe I’m ok with the voltage issue. I didn’t run the engine earlier because I was in the garage and had a gas leak at the carb check valve that I’ve since fixed.
Click to expand...
OK, the most important part is the cable fitment and alignment to the instrument. That square port should be clean all the way to its bottom, so the cable doesn't apply linear pressure or angular pressure. If you are working with the OEM cable, that square end can become slightly distorted or less than exactly square. It doesn't hurt to kiss it lightly with a fine file to get it closer to square. I have rotated them 90 degrees to find the best fit in a port that is also worn with age.
And about the dash illumination bulbs (4 of supplied by a orange wire), they operate through a dimming rheostat so there is going to be some voltage drop found there. And slightly above 13 volts is not a problem. Voltage regulator should allow 13.2 or so. Run the vehicle and maintain battery to just above 12 volts.
 
Ken71Twister said:
Also - with the engine running - the voltage at the instrument cluster plug is over 13 V. I also found another pin for dash lights that reads 11.9 V with the engine running. Maybe I’m ok with the voltage issue. I didn’t run the engine earlier because I was in the garage and had a gas leak at the carb check valve that I’ve since fixed.
Click to expand...
I would concentrate on voltage with engine stopped. Maybe I missed this--HAVE YOU CHECKED the battery itself with everything off, and again with key in "run" like as you make your measurements, only measuring at the battery? Maybe the battery is low or even defective/ worn out. Fully charged battery should be about 12.6. Any load on that is going to pull it down some, but even cranking, battery should be above 10.5
 
67Dart273 said:
I would concentrate on voltage with engine stopped. Maybe I missed this--HAVE YOU CHECKED the battery itself with everything off, and again with key in "run" like as you make your measurements, only measuring at the battery? Maybe the battery is low or even defective/ worn out. Fully charged battery should be about 12.6. Any load on that is going to pull it down some, but even cranking, battery should be above 10.5
Click to expand...
I just re-checked the battery. It is at 12.6 volts with switch off and 12.5 volts with the switch on.
 
RedFish said:
OK, the most important part is the cable fitment and alignment to the instrument. That square port should be clean all the way to its bottom, so the cable doesn't apply linear pressure or angular pressure. If you are working with the OEM cable, that square end can become slightly distorted or less than exactly square. It doesn't hurt to kiss it lightly with a fine file to get it closer to square. I have rotated them 90 degrees to find the best fit in a port that is also worn with age.
And about the dash illumination bulbs (4 of supplied by an orange wire), they operate through a dimming rheostat so there is going to be some voltage drop found there. And slightly above 13 volts is not a problem. Voltage regulator should allow 13.2 or so. Run the vehicle and maintain battery to just above 12 volts.
Click to expand...
I just looked at cable routing with cluster removed and it appears to be coming in pretty straight. No better option. I inspected the end of the cable and it looks clean and smooth. I looked at the head of the speedometer and see nothing unusual there. I repeated the speedo check with the electric drill and, again, it runs smoothly on the bench. I don’t know where the speedometer cable was made - I just wrote the seller and asked. The picture of the cable end shows that the flex cable is almost flush with the plastic head - which the speedometer shop tells me is the correct position. The second image shows my eBay receipt. Would the price suggest that I didn’t get a good enough cable?

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Price seems good to me.

Are the 2 screws on the back of the Speedo snug?

Are the rubber insulators on those 2 screws intact, m?
 
Dana67Dart said:
Price seems good to me.

Are the 2 screws on the back of the Speedo snug?

Are the rubber insulators on those 2 screws intact, m?
Click to expand...
Both screws seemed snug but one turned a few degrees with light screwdriver pressure. The rubber gasket under that screw looks like it is split - but nothing wiggles when I apply force to the speedo connection.

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The bottom one looks to be missing the rubber ( don't know if that would increase the noise) I suspect the shop did not repair it correctly

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There is sheet like piece of rubber isolator between this instrument and the housing also but none of this would prevent an audible clicking. It only prevents a low humming coming from a machine-like instrument and resonating through the dash.
If anyone needs to replace the 2 round isolators at screws, They are a generic item. Just I.D. and O.D. and Google search will find a package of 10 or more for mere coins. They likely will be a translucent silicone material instead of black rubber.
I think DMT has all in one package that includes the isolater at trip clock reset stem.
 
Thanks RedFish… I will purchase and replace the isolators. I just took each screw off and the “missing” washer was actually pressed down into the hole and hard as a piece of plastic. The other washer that was split broke when I removed it and it too was hard. Too bad that Mopar couldn’t supply rubber washers that would stay soft for 52 years.

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I came up with an idea while reading another thread where someone with a similar car corrected a speedometer clicking noise by replacing the speedometer gear (at the transmission). I’ve already ordered a new one. As a side-note ….in the late 80s the speedo gear stripped and I got another one from a salvage yard. I was ignorant of the importance of color and replaced a 34 tooth green gear with an orange gear (probably 40 tooth). I learned later that the speedometer was reading about 10% low. I’ve lived with that discrepancy for the past 25 years. It will be nice to get the correct 34 tooth speedo gear even if it doesn’t fix the clicking problem. I’ll pull the orange speedo gear to see if it has any visible damage that might be causing my clicking issue. I could even run the speedo with a drill from under the car to see if the speedo clicking noise goes away.
 
Interesting to note that one of the washers is shaped a bit like a top hat. The other washer is relatively flat. I wonder if the top hat shape is due to the washer being pressed into the hole and then turning rigid.

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