2nd Stewart Warner Problem

[Aggressor]

I have a long term unresolved problem with 3 of my Stewart Warner Deluxe gauges. These are electric gauges not mechanical. My Tach, Fuel Level, and Temperature gauges all jump up a few points when the light switch is moved from off position to the parking light or headlight position.
When the lights are switched on:
The tach will raise 200 Rpm.
The fuel level will raise to show approx. 1 1/2 to 2 gallons of additional fuel.
The temperature gauge will raise another 15 to 20 degrees.

The ammeter is uneffected as are all other gauges which are mechanical.
All gauges are grounded with seperate and individual wires.

The only thing common to all 3 gauges effected and the light switch is the gauge lights that they all carry.

Any ideas are most welcome.
-Geary

[Slither]

It seems like the electric gauges would work from the source voltage available in the system. I suspect that when you turn on the lights, there is a slight voltage sag as the alternator/battery supply current to drive the lights. In other words, the lights pull the source voltage down slightly due to ESR and other parasitic losses, causing the gauge readings to move with it. Just a guess...

[eliminator]

Geary,

How about the Altimeter Reading, is it effected?

Couldnt help it....

[Aggressor]

Rick it's all good. You're a clever and resourceful man with a quick wit that I've come to appreciate over the years.

Turn on the lights and the gauges will jump the stated amounts throughout the entire rpm range.
It's as if the twelve volt electrical "leg" to the light is running through the chassis of the gauge and giving it a cumulative voltage boost on its way to a common ground with the gauge.

Paul - Gut reaction makes me think the gauges are getting an electric "push" as opposed to sag.

It's these small things that do so much to make a person nutz.
As the say "I don't suffer from mental illness-I'm enjoying every minute".

-Geary

[RJacobsen]

Geary, have you tried removing the gauge lights temporarily to see what happens?

[mkassab]

I think Rod is on the right path. Also... have you put a volt meter on your gauge for readings pre and post lights on?

Is your alternator and wire heavy enough for the load?

Is it possible to try a different gauge? Or brand? To see if the issue follows it.

Keep us posted.... Mark

[eliminator]

Just to throw something out there that I have always though about. Our bulkhead, the steel frame that holds the doors and dash is sitting on top of the interior fiberglass. Now everthing is grounded to this steel frame but if the bolts that go through this framework to the frame don't have a good ground what happens. When I built my car I used a heavy star washer on top of the bolt head so the bolt head would have a good groung to the steel bulkhead and the a star washer under the car next to the washer and between the frame so that would complete the ground, so when you torqued those bolts down it would ensure a good ground between the steel bulkhead and the frame.
In therory it's possible for those bolts to be just centered just enough that they never make contact to the frame.
Just something for all the electrical wizzards to digest.

[Slither]

Geary, have you tried removing the gauge lights temporarily to see what happens?

Doubt it will change anything, but I'll be interested in hearing the result if he tries this... the lights are separate CKTs.

Paul - Gut reaction makes me think the gauges are getting an electric "push" as opposed to sag.
-Geary

That's because you are assuming that the rise in the gauge reading must be caused by an increase in voltage... which at first glance would seem logical. But the gauges likely move in the opposite direction of the source voltage because of their design, i.e. when the source voltage goes up the readings go down and vice-versa.

The senders are typically resitive elements, and I suspect they work in a voltage divider or a bridge CKT. If the source voltage sags, the reading changes. Easy to sort out with a good schematic (I'll see what I can scare up online...). As was suggested, measure the voltage at the gauges under both conditions: lights on, lights off. I suspect you'll get different readings, and have your answer quickly.

If it stays rock solid, then I have another idea... but let's see this first.

Do you know what the resistance range is on the fuel sender empty/full? If I recall, SW uses something like 240/30 ohms empty/full, so a lower voltage reading would appear to the gauge as less resistance showing more petrol in the tank.

[RJacobsen]

Geary, if all of Paul's technical bla bla bla is correct (no offence Paul, your just way over my 12th grade edjamacation ) it would seem that your voltage regulation is at issue. Are you useing an old style regulator or the internal/add on type?

[Slither]

Geary, if all of Paul's technical bla bla bla is correct (no offence Paul, your just way over my 12th grade edjamacation ) it would seem that your voltage regulation is at issue. Are you useing an old style regulator or the internal/add on type?

Only guessing here Rod, so I could be off in the weeds... certainly wouldn't be the first time I was wrong... or the last, unfortunately! I looked briefly on the net and didn't find anything on the guts of the gauges, just simple wiring diagrams... need to see how they work to be sure of the cause. Anyone else see any fluctuation of gauges turning on lights?

By the way Rod, since your car is so newly refurbished, you need to check the connections to the bla bla bla bla bla in order to protect bla bla bla and make sure that bla bla - bla bla doesn't burn out the bla bla... get it?

[RJacobsen]

By the way Rod, since your car is so newly refurbished, you need to check the connections to the bla bla bla bla bla in order to protect bla bla bla and make sure that bla bla - bla bla doesn't burn out the bla bla... get it?

Now THAT I can understand

[Aggressor]

Paul, You're logic is starting to sink in a bit.
The regulator is modern electronic under a vintage cap.
The charging system has been professionally checked twice in the last month and seems to be fine.
I won't be able to check anything until Monday as we're leaving for a wedding in Marietta Ohio.
I appreciate the responses and will report back with Monday's results.

- Geary

Food for thought - Why is the alternator Stator terminal not hooked up to anything when you are running an ammeter? Battery, Field, and Ground are connected but no Stator?

-Geary

[Naumoff]

Good job Geary. You are so good you replicated the crappy British electrics.

[Aggressor]

Tony

I read your response a few minutes ago - still laughing.
God Bless Lucas.

- Geary

[dmswann]

The reason the British drink warm bear is because they have Lucas refrigerators!!! God bless, GE, Whirlpool, Kenmore, Maytag, etc.

[Naumoff]

Tony

I read your response a few minutes ago - still laughing.
God Bless Lucas.

- Geary

Glad I could help. You forgot a piece of copper tubing.

[scott h]

not to highjack your post, but my SW ammeter just got stuck fully pegged to 60+. didn't see when it actually happened but needle stays there all the time, running or not, key on or off, and even when battery is switched off. is the gauge bad ?

[Aggressor]

Scott
Pegged without power from alternator or battery. No electric push from either side - must be a bad ammeter.

- Geary

[Aggressor]

The problem turned out to be the use of a Painless 12 Circuit fuse panel. The panel provided all the circuits, terminal block screw connections,fuses,etc that I required when I built the car. Among the connections included were Battery+ Feed, Alternator Battery+ Post, Battery+ to Ignition Switch, and Battery+ to Light Switch. When I wired the car, I wired the alternator battery+ post to the ammeter then from the other ammeter terminal to the panel connector. The opposing battery+ lead was wired from the starter relay to the Battery+ feed connector on the panel.
I had no concept that these two opposing positive forces would seemingly not know of each others existance in the bowels of the painless panel. This explains why my ammeter rarely moved in either direction and why I ended up with odd charging problems over the years of ownership. I removed the alternator connection from the panel routing it to the starter relay battery terminal. This got the ammeter swinging to the charge side but it would not swing to the discharge side. Additionally the three gauges still are still boosted by the light switch. This was until I moved the ignition switch + lead from the panel to the alternator terminal on the ammeter. Now the ammeter functions normally but the light switch boosts the ammeter instead of the three gauges. The final step was to remove the light switch + feed from the panel and connect it also to the alternator terminal on the ammeter. Now my headlights don't dim at idle and my blue high-beam indicator light is bright enough to be annoying.
All systems up and running nominal... for about an hours drive when my turn signal switch on the column failed.
God Bless Lucas - Keep the Faith Brothers -For this too shall pass.
Thanks for all the help and suggestions.
-Geary