[S_Cal968]

In the last week I too fell victim to the dreaded 16 volt gauge reading. I've seen a thread or 2 on this topic and this idea may solve more than one issue. Like many, my first instinct was to rap on the dash and cluster to no avail. Being the curious person that I am I decided to disect the gauge cluster.



First to narrow down the possibilities I checked the voltage at the battery with the engine running and all was fine. I loaded up the alternator, again all was fine - this pointed to the gauge.



See this past thread for Dave's cluster removal detail:

16V Thread [3/05]



Note: The cluster can be removed w/o removal of the steering wheel, but it's not easy. If the designer moved connector "C" up just .25" it would make life much easier, [it'll make sense when you see the pic..].

Note: Use extreme caution when disconnecting the 3 connectors the locks are fragile! They are un-locked by moving the lever up slightly, [~.008"] and then moving it away from the center. The levers should move easily, avoid forcing them! Also, I found it easiest to remove the connectors on the rightside first, [C & B] and then A [left side]. I'm convinced they must have had some guy with small hands at the factory...







Anyway once I had the the cluster out, I applied 12v to the gauge via C5 & C8 using a power supply. Note: One side of each light is common to C8, I used the Tip contact, [see pic]. I noticed that as I ramped up past 7.0v the gauge shot up to 16v. I touched and wiggled the components and sure enough when I touched the calibration sweep-pot the voltage dropped. I attempted to adjust the pot and would end up coming back to where the factory had set it.

The problem with this type of variable resistor is after many years of vibration the contact point wears out. There's 2 ways to fix a v/r, 1) replace it or 2) add a resistor to mechanically move the set point, but electrically it would be the same. Since I had some resistors, I opted for #2. Using a decade box, DMM and power supply I found a resistance that worked. With the additional resistance in parallel to the [220 Ω] v/r, I found that ~200 Ω [+/- 30 ohms] resistance would work. I carefully soldered the resistor in place, [don't try this after caffeine - there's very little room]. I then hook-up the power and re-calibrated the gauge using 2-point calibration.

















While I had the cluster out I checked all lamps - they'd be a bear to get to with the cluster installed. To get the cluster back in I had to slightly splay the dash just enough to clear the connector along the bottom. Once it was in I reversed the disassembly process.



I hope this saves some folks from buying a new v. gauge, voltage reg. and/or alternator.... <img src="/forum/images/smilies/968/cool.gif" class="smilie" alt="" />

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[Greimann]

[quote name='S_Cal968' date='Feb 18 2006, 08:41 PM']I hope this saves some folks from buying a new v. gauge, voltage reg. and/or alternator....  <img src="/forum/images/smilies/968/cool.gif" class="smilie" alt="" />

[right][post="16209"]<{POST_SNAPBACK}>[/post][/right][/quote]

Damn, Dr. Frankenstein. Nice laboratory. <img src="/forum/images/smilies/968/ohmy.gif" class="smilie" alt="" /> I think you have just signed up for a voltage gauge repair service.

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[Simuse]

Wow - great info and pics!

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[flash]

very nice!!!



ok - i'm about to pull my cluster for somethign else - since i have the power pulleys and consequently drop down in voltage at idle, and these gauges are not known for being accurate, i want to recalibrate mine anyway - can you elaborate on that process?



good timing

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[S_Cal968]

This gauge is not real accurate to start with, it's a step above an idiot light - more for showing an abnormality.

If you have an adjustable power supply and a digi-DMM, hook-up the power as shown in the pics above. I checked/adjusted the reading at both 12.0v and 14.0v, which as you know is the nominal operating range. Depending on what angle the gauge is viewed, it can off .30v, [aka: parallax error].

HTH

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[flash]

okee dokee - sounds pretty standard - then just rotate the giz-hatchy until i get what i want - cool

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[Brian]

great write up and pics!



i'm planning on cleaning up my gauge contacts this week/end. those pics really help.



i'm going to ask the question....

after doing all the work to remove the i.p., is there another voltage gauge that we could slap back in there that would work better than the stock one?



and how about an over-the-top question... any companies ever come up with a modern i.p. to replace the stock one? perhaps something digital or with lit gauge needles? just thiking out loud...

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[S_Cal968]

Thanks... <img src="/forum/images/smilies/968/cool.gif" class="smilie" alt="" />



I'm sure there are better quality gauges available, but you'd have to fab a bracket to work with the modular cluster. If it was for a track car, I'd yank everything out and start over. The cluster uses edge-mount connectors which isn't reliable to start with. And, the quality/precision of the stock gauges has a lot to be desired.

While I was in there I noticed they use a standard bulb for illumination [I can't recall the number..?] and if desired, opt to replace them with a different color equivalent.

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[SILVY968]

If anyone has a cluster out, could you please post a pic and the part number of the lamps that are used to back light the "parking light" green panel?

Mine is out and I want to have one in hand when I pull the cluster. I do not want to reassemble the cluster to drive down to the store and buy one.

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[Brian]

i've got mine out.

i'll check tonight.

from what i can tell, there are only three different types of bulb back there.

i wonder if i can get them at an autoparts store or if i have to go to a dealership?

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[durtkillon]

This is a great thread. My voltage meter was reading 16 any time the ignition switch was turned on (alternator running or not). This guide led me right to the variable resistor. I lucked out. Once calibrated, the POT had a new position and everything is perfect. I did not need to replace it or add a fixed resistor. Woohoo! The voltage guage alone is $600 bucks for this car from the dealer. Thank you S_cal968, wherever you are. <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />

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[Cloud9...68]

This is the first time I'd seen this thread. What exactly is the "dreaded 16V problem"? A reading of 16 volts on the voltmeter, apparently. I don't remember hearing this was a common problem with these cars. Great write-up, in any event. Impressing Dave Greimann is no small feat!

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[durtkillon]

I think this issue is fairly common on these cars. When doing searches on RL and Pelican, a lot of threads went down the path of votage regulators or swapping the meter out with a salvaged unit. One chap even swapped his voltage gauge with another bad one and didn't fix it until he found a third. That troubleshooting ala shcool of hard knocks. The interesting thing here is that they are repairable and calabratable. My voltage gauge now reads just over 12 volts without the alternator and about 13.4 with the alternator.

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[Cloud9...68]

Thanks for the explanation. It's just odd that I'd never heard of the problem before, but then, I wasn't aware of the weak early connecting rods until pretty recently, either.



Edit: Hmmm, maybe this makes a case for having an accurate voltage gauge occupy one of the spaces in my upcoming console gauge set...

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[Lear35A]

I'm just seeing this thread for the first time. And I've had the dreaded 16v reading for some time. Hope it doesn't take as long to fix this as my engine.

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[chudson]

I just stumbled onto this also. Any chance there is a similar fix for the engine temp gauge that randomly jumps to full hot? Mine has done this since I got the car. I know the engine doesn't overheat, but when it's stuck to the top of the sweep one can't be certain. My fear is that it really overheats one day and I shrug it off as being that weird gauge thing again.



There's s thread here somewhere that describes some sort of special resistor (if I remember correctly) that someone once mentioned would cure the temp guage but no one had a clue where to source it. Any idea / comment?

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[eurocarnut9xx]

After reading the fantastic write-up by S_Cal968, I too decided to attempt a fix of <acronym title='model year'>MY</acronym> volt gauge (voltmeter), which was stuck at 16V. This had started a couple of months ago, pegging to 16V. What was interesting to me was that at one point following this failure it read normally – but this didn’t last long. This was important as it indicated an INTERMITTENT failure. S_Cal968’s informative write-up was very useful in troubleshooting. <acronym title='model year'>MY</acronym> experience was slightly different however, so I’ll share those points and a couple other things I learned next.



1. When applying a test voltage to the gauge using ‘connector C,’ pin 5 is positive (+) and pin 8 is ground (-).



2. If the volt gauge is still installed in the cluster, applying test voltage will over range the oil pressure gauge. The safest be would be to remove the gauge. I did not do this, and <acronym title='model year'>MY</acronym> oil pressure gauge is working fine.



3. The 220ohm sweep pot is a carbon film, linear, 270 degree sweep, variable resistor. Electrical connection between the terminals and the conductive carbon film is achieved mechanically by the eyelets (or grommets) that attach the terminals to the PCB base the carbon film is on. This is where I (accidentally) found <acronym title='model year'>MY</acronym> problem. I had developed a high resistance connection between the terminal and the carbon film, of about 700ohms. This put the volt gauge way out of spec. I resolved this by (very very very) carefully using small tweezers to crimp on the eyelet that connects the terminal. After verifying continuity of the newly crimped connection I tested the variable resistor. From the center tap to each of the legs (only one of which is used) I achieved smooth, linear resistance measurements. (Note: before crimping, some electrical contact cleaner may be good to remove surface oxidization and improve your crimp effectiveness.)



4. I calibrated the gauge using a variable DC voltage power supply. While calibrating I used an additional meter to monitor voltage while I monitored current on the power supply. Do not apply more current than is necessary to develop your test voltage! This is a quick way to burn things up.



5. Relevance. The other gauges in the cluster share similar construction to the volt gauge (i.e. same type of carbon film variable resistor). Failure of this component may be intermittent, and could be indicated by readings that are off a bit, or pegged. Depending on the gauge this could be high or low. So it is feasible that this issue could be causing CHUDSON’s engine temp problem. The challenge in this one comes in calibrating it if the factory setting is altered. (Do we have datasheets for the RTD used in the temp sensor?)



6. If one wanted to attempt fixing a non-volt gauge problem, I would recommend measuring resistance from the tap to the carbon film right at the eyelet. Record this measurement! This is your calibrated resistance! Then use this resistance as a guide when repairing the eyelet. It may not be possible to get the resistance across the carbon film-eyelet junction to 0ohms, but any offset will need to be accounted for in the setting of the variable resistor. Once you are satisfied with the resistance of the junction, set the resistance from the center tap to the used terminal the value you recorded earlier. This should give you the same readings you had prior to the failure.



I hope this is useful. If you have any questions or would like to discuss, please just let me know!

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