1966 chrysler fuel gauge testing (NOT sending unit)

[Gerald Morris]

Just dropping this here for posterity.

1965 Chrysler 300 4dr hardtop 383 Auto

My fuel gauge suddenly is on the fritz this spring. Has worked as it should for the lifetime of the car.

Surprising it lasted so long.

Occasionally now when I start the car (or turn the key into accessory) the fuel gauge does not move... or moves after some time (*several minutes) of the car being started, but very slowly. Sometimes it works fine... sometimes nothing.

I ran a ground wire from the battery to the sending unit praying that was the issue. Turned the key on, no movement in the gauge. Damn. Not the sending unit.

Nope. When they go, they usually go out all the way. Either the float fills up, or the crude potentiometer windings in the sender finally break with age and poccasional moisture corrosion. The little wiper from the float arm might also break. Anything except the float warrants full replacement. I've been reasonably lucky with the sino-repops, having bought two, both of which work, amazingly enough.

Am fearing it is the Voltage Limiter/Regulator... ....

Really trivial bro. You can either replace it with a true OEM sort for anything from $15-500, depending on the vendor, or get a solid state one made to fit the instrument panel for ~ $55, OR, get a good generic 12VDC=>5VDC convertor, and then wire it into your old stuff. I did that for a little while, with some so-so results from the old sending unit, then got a NEW sending unit and new Autogage fuel gauge wired for 12 VDC which works beautifully. Then our '66 got wrecked. Still have the fuel gauge and am using the new sender in our '68 w the original instrument panel stuff, for the present. The stuff yields fairly accurate data. as far as I can tell when pumping petrol.

Think this is what has happened as I was driving the other day and Fuel gauge was not working and then ALTERNATOR gauge pegged hard to the top... and let out a big puff of white smoke... and now it dead in the water. Literally tinted the actual gauge glass with smoke from the inside too. The Fuel gauge also stopped working. Lame.

DANGEROUS! For NOW, lug together the red and black leads to that old ammeter, bypassing it. The best place for this is on either of the terminal studs which the leads were attached to. Just make SURE you pick just ONE. Those old ammeters can burn up your car man. Add a 3rd wire to the stud, and feed that to an after market VOLTAGE meter. This will give you a fair idea of how your alternator is charging. Look up the MAD bypass if you like, for more information.

So the whole cluster will have to come out. Terrifying. Think I will just live with it for now. Nothing like having NO fuel reading.

If you don't lug off that shorted out ammeter, you won't have to worry about any instruments soon. Be sure and do this ASAP. Its a SERIOUS hazard.

**UPDATE
Oddly, I went for a drive last night and the Fuel gauge came on after driving for a while, so it is not totally dead. Just working when it wants. Fingers crossed it doesn't go up in smoke too.

It will with the rest of your instrument panel if you don't get RID of that bad ammeter connection.

 

[Gerald Morris]

My issue has been solved mostly. The float has been changed out and the gauge now works. It doesn't read accurately except when you first start the car. When you start it up, the gauge goes to the correct reading, and then slowly falls to about half of the correct value.

Get a good "limiter" for the fuel gauge circuit. Go with the solid state one. The rest of that **** belongs in a museum, just past the Bronze Age batteries the Egyptians made then had no use for.

 

[darth_linux]

Get a good "limiter" for the fuel gauge circuit. Go with the solid state one. The rest of that **** belongs in a museum, just past the Bronze Age batteries the Egyptians made then had no use for.

Mines made by “Standard”, not sure if it’s solid state or not, but it’s new and working perfectly.

 

[YellowBird]

lug together the red and black leads to that old ammeter, bypassing it. The best place for this is on either of the terminal studs which the leads were attached to. Just make SURE you pick just ONE.

Is this done on the back for the cluster? I have to pull the cluster it out to access this? Or can be done from the bukhead/motor side? Not familiar. Wiring is not my specialty.

Look up the MAD bypass if you like, for more information.

Looked this up. Seems like running a 10ga wire from Alt to the the Starter relay, with a 16 or 14ga fusible link. Help distribute the draw.

 

[Gerald Morris]

Mines made by “Standard”, not sure if it’s solid state or not, but it’s new and working perfectly.

The Standard unit is Old School, but as well made as such can be these daze.... Hope you didn't pay too much for it. It should serve you well for some years.

 

[Gerald Morris]

Is this done on the back for the cluster? I have to pull the cluster it out to access this? Or can be done from the bukhead/motor side? Not familiar. Wiring is not my specialty.


Looked this up. Seems like running a 10ga wire from Alt to the the Starter relay, with a 16 or 14ga fusible link. Help distribute the draw.

You better find somebody who IS competent with electrical issues, and disconnect that ammeter. You have two hot wires connected to an old instrument which already showed clear sign of major failure. IFF it burned through cleanly, then you will likely just run your battery dead soon, unless some soul ran something as a half-***-bypass. By connecting those two leads together, you will complete the loop between the battery and the alternator. ALL the charging current from these old cars ran through that stupid ammeter until the early 1980s. Right now, you're not charging your battery, if nobody has bypassed the ammeter.

The wire size needs to be large enough to allow for the ampacity of the alternator and the load your vehicle places on it. 10 gauge was used for the old 1960s 60 A alternators. 12 gauge got used with plenty older vehicles running the 37 or 40 amp alternators. People really DIDN'T understand electricity well at ALL 60 yrs ago, and sadly, too many still don't, which bodes ill for the future.

Run AT LEAST a 10 gauge wire as per the MAD bypass if nothing else. I use 8 gauge, and actually have an improved bypass, but I'm not going to lay that on you. You can look it up if curious. Realize this: LOW voltage such as 12VDC more rapidly degrades per unit distance of conductor as a consequence of simple Ohm's Law. Oversizing conductors never hurt anyone. The converse has harmed many.

 

[darth_linux]

The Standard unit is Old School, but as well made as such can be these daze.... Hope you didn't pay too much for it. It should serve you well for some years.

Think I paid $35.

 

[Gerald Morris]

Think I paid $35.

Bad, but not the worst price I've seen. I recall now when you got this one. Some months back, right? God-willing, this should do for you for decades.... I have a couple old ones as spares, but likely will go with the RTE one soon enough. Need to replace my exhaust later this summer. Then the front suspension this Fall. THEN some more dash wiring.....

 

[YellowBird]

Run AT LEAST a 10 gauge wire as per the MAD bypass if nothing else. I use 8 gauge

Will do. Thanks.

You better find somebody who IS competent with electrical issues, and disconnect that ammeter.

On it! Honestly didn’t know about this design flaw. Appreciate the info and urgency.