5V conversion help needed

Hi, I put together one of the transistor/capacitor 5V convertor tricks for my gauges.
I hooked it up as in this picture with the input pin attached to the red wire, and output is the orange wire. It puts out 5V. WHen I installed it, I get nothing. Guages were tested and work. Two possible reasons it does not work:

1) I have the blue ground wire going to the steering wheel support, not the pot metal of the dash cluster.
2) Dash cluster also has a ground wire going to same point on support. Ground is ground, so I think I'm OK to discount this reason
3) WHile I did put some red shrink wrap on the terminal at I (red wire connection), I used a metal speed nut to hold down wire. Maybe I need to use a rubber washer before putting on speed nut?
4) You tell me.

THe regulator inside gas gauge is disabled.
THanks for looking.

All I can see is a red and orange. The orange is indeed hooked to where output should be, that is the jumper trace between gauges

You are trying to insulate the stud from the red wire? Double check to be sure that is the 12V and not the sender

All I can offer... Ring terminals beneath speedy nuts for connections are too iffy. The speedy nuts tended to loosen over time even when they had full circumference footing.
So a better way... Place the speedy nuts just like OEM ( no shrink or isolation required ). Place the ring terminal on top of the speedy nut. Internal tooth washer and standard hex nut on top or the ring terminal. The attempt to isolate your red wire from that gauge post seems odd to me. You say the limiter is somehow disabled ( I wont get into the "bend the little thingy" BS here ).
Although it doesn't really matter where you tie into the 12 volts, the fact is red wire/12 volts no longer needs to go to that gauge at all.
Blue with white tracer in that round multi pin connector is switched 12 volts. Just tap your red wire into that. Where that blue with white serves no other purpose/component you could clip it from the round connector and make it to your red with male/female spades ( insulated female on the blue w/white of course ). Plus the different connector types means more difficult to hook up wrong in the future. Your orange wire could be placed on the wrong post in the future. Its in the right place today just not in a very good manner. Hope this helps

I've also built a few of these and produced a "How To Guide" as well, here's a few photos which might help.
It seems to me that you are still supplying 12v to the gauge/regulator and have not totally isolated the 12v supply from the printed circuit. Photos are showing 1964 Dodge Dart instruments, with the regulator built into the fuel gauge.

On yours, I interpret the pin with the red coloured wire as the former 12v feed to the gauge, cut that pin off so you are guaranteed not feeding the gauge 12v...


Then, insulate the casing to prevent electrical contact...

Now, insert brass bolt from inside of circuit board and connect brass spade terminals externally (as shown) to create a 12v supply to your NEW regulator, completely independent of the gauge...


Then, connect your regulator (I eventually housed mine in a headlight relay can) and conduct a test...


Also, feel free to email me and i can send you a fifteen page PDF copy of the "How To Guide"...

unbelievable what some come up with. That beats all I have ever seen. I can just imagine the do it yourselfers cracking that fibrous backboard in attempt to cut a stud off. Good luck to all.

RedFish said:

unbelievable what some come up with. That beats all I have ever seen. I can just imagine the do it yourselfers cracking that fibrous backboard in attempt to cut a stud off. Good luck to all.

Click to expand...

I just CAREFULLY cut mine off using a jeweller's hacksaw. No problems...

So the backboard in your example is still light colored, flat, quite nice considering its age. Others will find them darkened, warped, and extremely brittle.
If you'll go back and look at it long enough you might finger out none of that was necessary. All anyone needs to do is isolate this 3 post/2 part gauge from chassis ground. Clip the 12 volt wire from the harness connector and route it directly to their supplemental limiter/regulator. Now the copper trace is dead. The stud is no more than gauge support.
No hacksawing, no opening the gauge to bend the little thingy, nothing more than the piece of tape on the back. One could remove that little slither of metal captured there but... that will leave the board a little loose. Again, not necessary. Just cover it with tape or otherwise block it from the housing contact.
The internal limiter is just like any other electrical component. It cannot do anything good or bad if it doesn't have a complete current path (+) -> (-). If the fuel gauge part of it is good it will function just like its 2 post thermal gauge neighbors. But wait... If we cut away the 12 volt going there already, Why do we need the piece of tape? The other current ( 5 volts ) coming in from anywhere can back feed through the original limiter. If grounded it would act as an additional, very faulty, gauge of sorts. So the little piece of tape equates to disconnecting a sender in this current path.
There was a 8 year period when owners would send their gauge(s) to me for service and I would open all of them. For this type gauge I would completely remove the limiter. 95% of the fuel gauges needed the thermal gauge part renewed anyway. That's relative to their duty. The work higher/hotter than their neighbors. Deleting the limiter just for easier reassembly.
Hell I even offered gauge exchange for some models. I aint seen it all ( this thread proved that LOL ). After 8 years a few hundred various gauges, I decided I had seen enough.

RedFish said:

So the backboard in your example is still light colored, flat, quite nice considering its age. Others will find them darkened, warped, and extremely brittle.
If you'll go back and look at it long enough you might finger out none of that was necessary. All anyone needs to do is isolate this 3 post/2 part gauge from chassis ground. No hacksawing, no opening the gauge to bend the little thingy, nothing more than the piece of tape on the back. One could remove that little slither of metal captured there but... that will leave the board a little loose. Again, not necessary. Just cover it with tape or otherwise block it from the housing contact.
The internal limiter is just like any other electrical component. It cannot do anything good or bad if it doesn't have a complete current path (+) -> (-). If the fuel gauge part of it is good it will function just like its 2 post thermal gauge neighbors.
There was a 8 year period when owners would send their gauge(s) to me for service and I would open all of them. For this type gauge I would completely remove the limiter. 95% of the fuel gauges needed the thermal gauge part renewed anyway. That's relative to their duty. The work higher/hotter than their neighbors. Deleting the limiter just for easier reassembly.
Hell I even offered gauge exchange for some models. I aint seen it all ( this thread proved that LOL ). After 8 years a few hundred various gauges, I decided I had seen enough.

Click to expand...

Hi RedFish,
Thanks for that reply, what you have written makes sense now after having done my own. The problem I had was I'm on the opposite side of the planet to you guys, no access to over-the-counter spare parts and therefore I had to come up with my own solutions (remarkably similar in many ways) BEFORE I discovered what others had already been doing.
Mine works perfectly, just proves there's more than one way to skin a cat...

If the car in question is a 1964, you should have searched for my post
www.forabodiesonly.com/mopar/threads/fuel-gage-fix-64-valiant.269976/
Your fuel gage terminals look different than mine.

I tweaked the Vreg output so that the temperature gage read correctly (test resistors) and added resistance in parallel to trim the fuel gage to read correctly w/ the new fuel gage. The gages also have mechanical adjustments (a bit tricky).

BillGrissom said:

If the car in question is a 1964, you should have searched for my post
www.forabodiesonly.com/mopar/threads/fuel-gage-fix-64-valiant.269976/
Your fuel gage terminals look different than mine.

I tweaked the Vreg output so that the temperature gage read correctly (test resistors) and added resistance in parallel to trim the fuel gage to read correctly w/ the new fuel gage. The gages also have mechanical adjustments (a bit tricky).

View attachment 1715128431

View attachment 1715128432

Click to expand...

Bill, where did you get the ohmic values from? Just curious I plan on building a gauge tester very soon.

64_Barracuda said:

Bill, where did you get the ohmic values from? Just curious I plan on building a gauge tester very soon.

Click to expand...

I'm not Bill but I have an answer... The pic is of the label on the tester that dealers service tech used. I don't think anyone knows who added those ohms values to the pic but they are pretty much correct. The senders have a 80->10 ohms range. 80 ohms should generate no needle movement, thus a invalid test. Approx' 74 ohms will move a needle up to the 1st hash mark in most examples.
Approx' 23 ohms is the center of the range.
10 ohms should get high end of range. In most examples that needle position, like the 80 ohm or home/off position, is set with physical stops.
Lesser ohms/resistance for extended period will overheat a gauge.

Thanks RedFish. The resistance chart is not my photo. I filed it away from this site where guys trade very helpful info. Sorry, I don't know who to credit for posting it. The fuel sender limits are given many places (some variances). I recall seeing more commonly about 10 ohm (full) to 70 ohm (empty), often on after-market gages. Of course, every sender varies. Most important is to set your empty reading correct so you don't end up walking. The temperature sensor range is harder to find. All my 60's Mopars have just an on-off lamp for oil pressure.