{Chrysler 300} Re: 1964 voltage limiter/ temperature gauge

["D.C. Mason" <petergriffinforpresident@xxxxxxxxx>]

John/Bob/all,

The dead temperature gage in the 64 300 sport turned out to be a bad circuit card.  

I did pull the instrument cluster and replaced both the fuel and temp gauges, then reinstalled and still nothing.  Checked continuity along circuit card trace from 12V in and it was open/flaky.  Pulled card and took picture of damage.  Guess the trace burnt at some point in the past?
 

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Replaced circuit board and now have temp and fuel readings.  Temp reads high, fuel reads low.  A resistor in series ala Carl Bilters tech article will fix the temp reading.  Ten ohms may be a bit high; will check again but probably need more like 5 ohms.  Trying to get 180 degrees at top center.  

Will check and clean fuel sender contacts then go from there on fuel gauge.  

V/r
D&K


Sent from my iPhone

> On Jan 2, 2023, at 9:50 AM, D.C. Mason <petergriffinforpresident@xxxxxxxxx> wrote:
> 
> Hi Bob/John
> 
> Thanks for the reply!  Sender is good and I have actually seen a significant variation in the ohms readings of brand new ones.  The lower the ohms the better, because then you can do Carl Bilters trick of putting a 10ohm resistor in series.  When the resistance is too high out of the box, it will never read right (always will read low I think).  
> 
> Well I guess I’ll be removing the dash cluster from the 300 sport then.  I was wondering if the power at “I” was necessary for fuel gage; was hoping it drew its power from “A” like the temp gauge does.  I was going to do the solid state limiter install from behind the dash laying on the floor to avoid instrument cluster removal.  I’ve removed these Instrument clusters before and if you aren’t careful you can scratch stuff up.  The good news is I have a few spare instrument clusters so no problem getting another fuel and temp gauge.  And while I have the cluster out, I’ll lube the speedo cable.  Do you guys use axle grease for that?
> 
> If the “I” post is totally isolated from the 12V input on circuit board, and you are only feeding 5V to gauge at “A”, you can still get feedback from “I” and blow up the 5V limiter?
> 
> The main reason I had planned to install the solid state limiter vice replacing the fuel gauge is that as I understand it, the mechanical limiter is a sketchy design in that if it fails closed it will burn up gauges with full 12V.  Anyway, I’ll Replace the gauge(s)  today.  Get ‘er done!  😆
> 
> Thanks!
> D&K
> 
> 
> Sent from my iPhone
> 
>> On Jan 2, 2023, at 8:18 AM, Bob Merritt <bob@xxxxxxxxxxxxx> wrote:
>> 
>> 
>> Carl Bilter wrote a page on how to correct for
>> an improper sending unit.
>> See http://www.chrysler300club.com/how/tempgaugefix/1.html
>> 
>> Bob
>> 
>> 
>>>> On 1/2/2023 8:04 AM, John Grady wrote:
>>> Hi Dave , you thinking is absolutely correct , however you cannot leave the remains of the V limiter connected inside gauge to your new ps . It will feedback to 12 v inside the gauge and blow up your 5 v . Also the gauge with the limiter won’t be powered by the new supply if you just  disconnect the post altogether .
>>> This means opening the gauge and removing the mechanical pulsing vr . My work has been on F gauges but same design  but more open to get at and do that .I used 7805 chip , and a capacitor . Chip needs heat sink use metal of dash can and 3 wires soldered on chip . See chip sheet on line .
>>> BUT , are all your gauges reading wrong ?
>>> If others reasonably ok , problem is temp sender . Very common as what they sell us now as replacements are wrong calibration .
>>> Went all through this like you , realized replacement sender is chinese junk now.
>>> Fixed by removing sender from junk motor .
>>> You can go either way but with nice sealed up dash can if vr really is bad , I’d get another gauge . Easy from parts car . .Abd
>>> I doubt it is out of calibration given nature of it . This design of gauge is not very precision  even when perfect .
>>> Try sender from old motor …
>>> Hope  this info helps you
>>> John
>>> 
>>> Sent from my iPhone
>>> 
>>>>> On Jan 1, 2023, at 8:07 PM, D.C. Mason <petergriffinforpresident@xxxxxxxxx> wrote:
>>>> 
>>>> 
>>>> Hi Bob/John
>>>> 
>>>> Wanted to run something by you before trying it out and posting to the group.  I’m working on fixing a non-op temp gauge on the 64 300 sport.
>>>> 
>>>> Checked the sending unit center post wire (purple) continuity all the way to the gauge and it’s good.
>>>> 
>>>> Next, I put a spare instrument cluster on the floor and simply jumpered the posts from the one gauge to the other.   Got a halfway reading on the spare gauge whether engine was cold or warm.
>>>> 
>>>> <IMG_9726.jpeg>
>>>> <IMG_9728.jpeg>
>>>> 
>>>> 
>>>> I checked for voltage limiter volts and could see pulsing on the Simpson meter.  But I don’t know what it should exactly look like to see if it’s ok. So next I wanted to isolate a spare gauge and connect an independent 5V power supply to the one side and then jumper the sending unit purple wire to the other side.  Spare gauge in this configuration appears to read low at engine warm idle but at least not dead:
>>>> 
>>>> <IMG_9733.jpeg>
>>>> 

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> 
>>>> 
>>>> This brings me to my question.  I’m guessing the original fuel gauge voltage limiter is not up to spec.  So I plan to connect the 5V solid state power supply to the circuit board (power supply seen laying on the floor in the above photo).  The brand of the power supply is Merit.  Too bad it doesn’t have another R and T- but what could possibly go wrong?
>>>> 
>>>> On the circuit board at the back of the fuel gauge you see three posts marked I, A, and S.  The “I” is 12V in.  The “A” is the adjusted 5V out from the mechanical points type voltage limiter inside the fuel gauge.  The “S” is for the sending unit wire from the fuel tank.  The “A” power feeds the temp gauge.
>>>> 
>>>> <IMG_9735.jpeg>
>>>> 
>>>> 
>>>> Fuel gauge:
>>>> <IMG_9736.jpeg>
>>>> 
>>>> 
>>>> The approach is to use the 12V at “I” to power the solid state limiter and connect the 5V output of it to “A”.  In order to bypass the mechanical limiter in the fuel gauge, I was going to use a fiber washer between the nut and solid state limiter lug.  Also would put heat shrink tubing around the lower area of post “I” to prevent the solid state limiter lug from contacting the post.   Can then connect the 5V output to “A” with an alligator clip.
>>>> 
>>>> Sound reasonable?
>>>> 
>>>> If this is successful I plan to post the process to the list server.
>>>> 
>>>> V/r
>>>> Dave
>>>> 
>>>> 
>>>> Sent from my iPhone
>> 

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