hunt4cleanair

Very Nice Work D

DiCorv

thanks guys

DiCorv

Below I include my e-mailed answer to Ken on his ''always-on'' warning light in 77 vette, might be useful to others too :

Many things could go wrong in this system...
have you checked the sender in the tank for proper variation of its resistance from a few Ohms when Empty to about 90 Ohms when Full, or maybe about 27 Ohms at 1/4?
And if it measures OK, is this being transmitted thru the wiring up to the Module itself ?
If the Fuel Gauge shows the correct amount of fuel that you know for sure is in the tank ,and the Gauge itself is not faulty, then the sender is sending the correct resistance.
If a Gauge shows, lets say 1/4, but the sender is faulty or shortcircuited, or the wiring is shortcircuited someplace between Fuel Tank and Gauge, then the Low Fuel Lamp, given the Module is working correctly, would stay on. ( the shortcircuit, which is Zero or just a few Ohms, is interpreted as an empty tank ) .
On the other hand, the repair on the module might not bring it to correct working order, as for instance, what type of transistor was replaced with what.
In my case I was unable to source the obsolete Motorola transistors, and with the help of the forum I found out about the NTE159, but the second one was totally unknown to me and could find no data about it on the internet, so I tried and succeded with the BC337 that I used, still not knowing what an official replacement of the Motorola 6676 would be.
I must add that the original Motorola 6676 and the one I used , did NOT share the same Pin arrangement ,so had I just soldered the replacement exactly like the original ,on my circuit board, then the Module would not have worked properly!
Hope this helped a bit, each piece of this small wiring puzzle must be checked individually to make sure it works allright.
Maybe you could first try using a small 3-watt or more, 90 ohm variable (wire-not carbon) resistor in place of the sender to check your Gauge & Module ,the way I did.
One more failure possibility I now think of, might come from a faulty or ageing ''gauge cluster printed circuit board'' ,the one that the module plugs on.
There might be a cut (opencircuit) or a shortcircuit to the chassis of the thin copper wiring tracks that form the module socket...etc,etc

Anyway, always be alert that tampering with Fuel Tank containing flamable fuel + fumes inside along with Electricity that easily produces sparks, is not safe AT ALL !!!
Only if you are VERY familiar with electronics should you ''play'' with these!
Regards,
Dimitris ,79 vette

*also please note that I've made a small correction on circuit diagram posted 11-11-09 at the Ohms Listing in Test Measurements comment, where previous (now deleted) diagram showed them in reversed order*

DiCorv

A schematic I just did of exactly how my 1979 L48 Fuse Panel is.

hunt4cleanair

WOW...can you do one for a 78? There are some differences. for example, where the flasher is located (lower right) the wiper delay module is plugged in. I can provide what you might need.

DiCorv

It is not that easy to draw an accurate Fuse Panel, if one does not have the actual car or wiring harness to check and double-check the routing (using a continuity/Ohmmeter) whether it accurately relates to the (correct) printed wiring schematic that you ought to have at hand, anyway . In Repair Manuals, Shop Manual or GM 1978 Assembly Manual there surely is a similar sketch ,but always not that informative , that's why I HAD to do mine, it took me hours and hours while sorting out other stuff, mainly radio & antenna connections, (these are often found tampered and non original, also installed fuses are often found of different values than the GM specified), so I needed to make sure I can safely depend on the Fuse Panel ...
I 've not checked but others in Tech forum might surely have done the job for various years. But take note that an ''as original'' scematic should only apply to an original car, otherwise fuses will start to blow, the least, etc...
Dimitris

hunt4cleanair

D

I've got an original wiring harness...out of the car plus what's in the car. So what software did you use to sketch it and how did you do your continuity tests? Maybe I can do a 78 from what I have.

DiCorv

There was no special software to draw this sketch. It could have been drawn by hand too.
For starters I scanned an original 79 Corvette Fuse Panel sketch found in the GM Assembly Manual (easily obtained by Corvette America, Zip, etc) and using a photo editor (Corel Photopaint) I first erased obstructing lines or notes and then added my notes and colors that I had previously , carefully noted down by pencil on an enlarged photocopy of this helpful 3D Fuse Panel sketch...(had I not found the sketch in the manual it would be rather easy to sketch it from a straight on or 3/4 close-up photo of the actual Fuse Panel, although GM notes on it were more than helpful.
It may be feasible to track all or most of the wiring routes of your harness, provided you know all the components your harness different plugs connect to ( tag all identified plugs/terminals with small self-adhesive notes-I use white insulating electr. tape and fine-pointed black permanent marker to write on them). It should be preferable to have connected the Key start switch, and the route from Battery (actual Batt DISCONNECTED) to starter /alternator/ volt.regulator, so that you can identify the HOT route of Batt. voltage from Batt. to switch (and discover which circuit takes power at ''RUN'' position, or only at ''Start'' position, or stays ''alwaysHOT'' (like clock circuit, etc.) If you now connect alligator clip of one Digital Amp-Volt-Ohm Meter Probe to the connector that would go to the 12 Volt Batt. plus(+) terminal, and the Meter dial turned to the ''continuity'' position (where a beeper beeps at a circuitry continuity instance and also Zero OHMs are indicated) then the other meter probe can be contacted to (emptied) fuse slots on the fuse panel to find out which terminals take (+) at what condition (''always'', or at ''RUN'', or at ''START'' etc).Then the other fuse contact to the one found in continuity to Batt. can be traced the same way to discover the protected circuit/s. All this must be done carefully with much patience and always accompanied by the printed electrical schematic of exactly the year of the car, to identify and cross-reference the circuits and their respective cable color combinations.
The thickness of the individual cables is also included in these schematics and is very helpful in discriminating similar colored wirings... Be very careful with continuity meters that may beep to show a continuity in the circuit, but the OHMs shown may be in the range of some Ohms, tenths or hundreds of Ohms and still the beeper beeps: this means that some kind of low resistance component lies somewhere in-between check-points. It may be a Lamp or a rellay winding, etc- always follow schematic circuits to understand how everything works. Its quite complicated but once you get used to the method, you can ommit areas that do not include the Fuse Panel...
Once the original schematic circuits are identified, then you can proceed to identify all non-original wiring routes (if existent) of cabling that may at some time have been added to the original.These ought to alter the standard fuse values, hightened if additional components are found to be dependent to some fuse or other, and the opposite: if some component that was supposed to take power from a particular fuse was at some time moved to another circuit, then this fuse should accordingly be lessened in value, that is if you decide to keep alterations /additions/ modifications...
( In my case power to the rear brake lamps as well as Radio and Antenna power were taken from other places and I returned them to original spec. pick-up positions)
All the routings can be checked and noted, for ease, on the schematic using color pencils/pens simulating real ones. Also drawing a harness sketch, here and there and taking photos of ''as was'' proves very helpful in case you get stuck, especially if you come to dismantle an already installed harness. Best of all of course is to have a friend's same-year car to examine and ''copy'' routings and component positioning.

merry Christmas and a happy fast-driving year twenty-ten to all,
Dimitris, Athens

ddbjr

Did anyone find a cross reference at Radio Shack?

thanks
donald

0Willcox Corvette

I believe Rogers posted picture shows the aftermarket transistor part number.. ecg159

Willcox

DiCorv

Please take note that not both Transistors reference to an ECG159 or NTE159, only the one taking the Lamp load and it is a PNP type transistor. The other one is an NPN type, and no cross reference could be found what-so-ever, as much as I extensively searched all related web sites . But it is easy to set up the circuit by using a transistor similar to the one I used in my circuit adaptation-have a look at my post of 11-11-2009. I know of at least one other forum member who has successfully constructed the module using my posts, and intends to post comment.
good luck
Dimitris

danno12345

What a great thread!! I recently removed my gauge cluster to install a new radio, and found that the Low fuel light was non-functional. It looks like the diode had fried. Thanks to this thread, I found a 1N4005 laying around, and used it in place of the dead one. (1N4005 = 600V, 1N4007 =1000V. I figured that it would never see either of those voltages, so it should work.)

Now that I've replaced the diode, I'd like to bench test the thing to make sure it works before I put it back in the car.

Is there an easy way to do this? I know where Pos & Neg go, but don't know what else to do to make the light come on.

I was thinking I could just ground the third contact to simulate a completely empty tank, but that doesn't seem to work. It looks like from DiCorv's schematic that I need to put some sort of resistance between +12V & Gnd to simulate the fuel gauge, but I don't know what is an appropriate value.

I've got a whole pile of resistors, so any value needed I should be able to come up with.

Basically, I want to find out if all the other components are still good without desoldering & testing them, since I'm marginal with a soldering iron at best.

Thanks!!
Dan

bluthundr

The sending unit is 0 to 90 ohms. Per DiCorv's drawing, it should kick the light on at about 15 ohms.

danno12345

So if I ground the third contact (where the sender comes in), then the light should come on right?

It's not doing that, so maybe I've got some cooked transistors too.

Dan

DiCorv

Hi,the usual failure to this circuit is the NTE159 transistor that carries the load from the #194 lamp. In fact if one uses a higher wattage lamp that I know exist in the shape of the #194, then NTE159 dies.( for an easier life of transistor NTE159, I used an LED lamp in my circuit -observe polarity!-, but needed to also add the 2.2 kohm resistor across it -haven't tried it on an original module though). The next thing to check is the electrolytic capacitor because these components are the ones with the shortest life in electronic circuits. Check the diode for correct polarity and of course that lamp is not burnt. To bench-test it follow my photos and comments and use a 90-ohm (a higher value would work at the 0-90 ohm part) Variable Resistor (wire-wound to handle the 250 mA current).You may use of course separate resistors (>1-2 watt) of course, but you wouldn't be able to check exact turn-on point.
Good luck.
Dimitris/DiCorv

T_vette

Hello all

I'm Walter, a vette owner and enthusiast from Italy.

Some months ago I though I had a problem with the fuel-lamp module.

At the end of the investigation I discovered the module was ok... but I studied how it works and I decided to develop a better one.

In my opinion the mai problem of the original circuit is that there is no hysteresis: the lamp is slowly turned on and off and this lead to a too high power dissipation in the driving transistor. As Dicorv highlighted, the transistor may die is the wrong lamp wattage is used.
That's why I decided to develop a little bit more complex circuit (as you can understand, electronics is my hobby...).

I'm not (yet) able to directly insert a picture thus here is the link to the italian vette-enthusiasts forum I proudly belong: :o

http://www.corvetteitalia.it/forum/t...90&whichpage=2

Unfortunately I've not been able to find the customized lamp socket and I de-soldered it from the original module...

Also here in Italy there are many Vette lovers!



Regards,

Walter

worship79

This is an old topic, but it proved very helpful to me today! Thanks Dimitris

DiCorv

Thanks, it sure is an all-times useful practical piece of info, never old enough, yet!
Anyway, that is, until at last, one affordable new working module finally finds its way to the shops' shelves...

Dimitris

0Willcox Corvette

I now have the reproduction modules.. shelves should be loaded up by the end of next week..

DiCorv

Good news...at last...
Took 3 whole years for a reproduction of this tiny C3 Low Fuel Warning Module to reach shelves!
Lets spread the word!