Weird Electrical Happenings-Part 1, ...turning headlight knob effects full gauge Options

[7TPorsh]

I have a bunch of little weird electrical things going on...so i'll attack one at a time:

The fuel gauge (stock combo gauge) moves as follows under different conditions:

- Ignition off/headlights on- turning headlight knob up makes fuel gauge go from empty to full; turning down go back to empty.

- Ignition on/headlights on- fuel gauge show reading...turning knob up increases the reading on the fuel gauge by 1/4 tank; turning down decreases...so 1/4 fluctuation in the fuel gauge depending on how the headlight knob is turned.

Tend to think the full bright on the headlights translates to a closer fuel reading. But why? is the power source for the fuel gauge incorrect?

I checked the schematic, but it looks like a Lucas engineer designed the wiring for the combo gauge.

[Cap'n Krusty]

Check your grounds, then use the wiring diagram to trace the wiring. It's in color, which is convenient, because the wires are, too.

The Cap'n

[realred914]

I have a bunch of little weird electrical things going on...so i'll attack one at a time:

The fuel gauge (stock combo gauge) moves as follows under different conditions:

- Ignition off/headlights on- turning headlight knob up makes fuel gauge go from empty to full; turning down go back to empty.

- Ignition on/headlights on- fuel gauge show reading...turning knob up increases the reading on the fuel gauge by 1/4 tank; turning down decreases...so 1/4 fluctuation in the fuel gauge depending on how the headlight knob is turned.

Tend to think the full bright on the headlights translates to a closer fuel reading. But why? is the power source for the fuel gauge incorrect?

I checked the schematic, but it looks like a Lucas engineer designed the wiring for the combo gauge.

sound slike you have a misswire probelm. disconect the battery so as to not short anythign out, and get under the dash and trace the wires. seem like the full gage is being supplyed powewr that is meant for the dashboard lights (which are dimmable).

do you have a electric diagram, like from the haynes book? if so, use that as a cross check for teh wires, pay close attention tot eh wires on teh back of the fuel gage, and the wires that power the dash lights (all the dash lights should be daisey chained together)

the fuel gage should have a black and a green wire (if I read the small print on teh diagram right) thesetwo wires come from teh gas tank sendor there is a third wire on teh gage, a red and white one, for power


good luck

[Tom]

Did this just start after you made some repairs/modifications? If no, and it just started by itself, then I agree with bad grounds getting steadilly worse. If you did something and it started after, go back over what you just did.
Tom

[7TPorsh]

I think it has always done this and I just discovered it now that i want to start driving the car after 5 years on jackstands.

I'll check the grounds...which is the power wire? Hard to tell from the schematic...any pics?

I have a feeling the power is being sourced from the dash lights and not the fuse box.

[Tom]

Since it has been sitting for a while, I would expect that corrosion has taken it's toll on some connections. Check those grounds near the driver's footwell. Should be a stud with several connectors on it. Clean and inspect the connection well and hook back up. Let us know if symptoms change.
Tom

[Mike Bellis]

Electrical systems will do strange things when a ground connection is lost. Electrical circuts always search for "ground". An electrical ground is ONLY a part of the circuit that is "less positive" and not neccesarily a true ground. Your system has lost a true ground and is hunting for a "more negative" to drain the load. This means your ground is either disconnected somewhere or has high corrosion. This results in the "ground path" to find the least resistance back to the negative side of the battery. This can cause damage if not corrected.

[Tom]

Mike,
Very well put. Exactly what I was thinking. Didn't have the right words to explain it like you did. (IMG:style_emoticons/default/piratenanner.gif)
Tom

[7TPorsh]

Where are the ground connections points? Diagram shows a few, and knowing actual locations would be helpful.

Also, what are those little numbers on the wire ends and connections? They don't seem to sync up with each other and it's misleading...should i be grounding every loose brown wire?

[Mike Bellis]

Where are the ground connections points? Diagram shows a few, and knowing actual locations would be helpful.

Also, what are those little numbers on the wire ends and connections? They don't seem to sync up with each other and it's misleading...should i be grounding every loose brown wire?

In the front trunk, behind each headlight
under the drivers side dash, above fuse panel
in engine bay, behind drivers seat

Clean and inspect all 4 of these locations. Also inspect/replace the ground strap from the rear of the transmission to the chassis. Inspect the negative battery cable and connection points.

[7TPorsh]

Well i checked around...behind the front trunk pull above the fuse box was a bundle of brown wires (about 11) are twisted together. They weren't even grounded. Sheeesh!

So I put clips on them and grounded them to the frame behind the speaker cover.

Now the tach, oil pressure light and gen light work. Yahoo.

But... the gen light goes on now with the parking lights...not the headlights. Did I miss a ground or did i ground something I shouldn't have. The voltmeter goes down a volt or two when this happens.

Also Part Two problem isn't fixed with this.

[realred914]

Well i checked around...behind the front trunk pull above the fuse box was a bundle of brown wires (about 11) are twisted together. They weren't even grounded. Sheeesh!

So I put clips on them and grounded them to the frame behind the speaker cover.

Now the tach, oil pressure light and gen light work. Yahoo.

But... the gen light goes on now with the parking lights...not the headlights. Did I miss a ground or did i ground something I shouldn't have. The voltmeter goes down a volt or two when this happens.

Also Part Two problem isn't fixed with this.

the alternator light should have a postive power on one lead all the time the ignition is on, the other end of the bulb goes to the engien bay toward the laternator. when teh alternator is working it puts + 12 on this wire, which is the same as on the other wire to the buld, so there is no light (both wires to bulb now have +12 volts on them) if the alternator is not putting out +12, then the light still sees +12 on the one sid, but less than +12 on the other side, the difference between the two wires in volts is what will make the lamp glow. the lamp may nto glow if the waire have a msall voltage difference (say +12 and +11 volts so the differeance is only 1 Volt, no glow, but if the alternator starts to die and is only putting out +2 volt then teh lamps "sees' a difference of 10 votls (12-2=10) and it will glow then.
Note none of the two alternator light wires connect to ground!

so one of the two wires is some how hooked up to the parking circuit

Some clue would be helpfull,....

1.... does this do this when teh ignition is on or off or both?

2. does this do this when the engine is reved (supposedly the alternator is putting out a look of volts when reved)?

3. Does the alternator light appear to work normally otherwise if the parking lights are not used (ie glows with ignition on, but no engine running, and goes out after engine is started and reved?)


find out th e three clues above and post, we can work from there.

[Mike Bellis]

There is a dash light that illuminates with the parking lamps. White/Blue or White Green, I think. Make sure your dash lamps are connected correctly. If the alt light goes on with parking lamps and off with head lamps, I think the bulb is connected wrong.

[7TPorsh]

There is a dash light that illuminates with the parking lamps. White/Blue or White Green, I think. Make sure your dash lamps are connected correctly. If the alt light goes on with parking lamps and off with head lamps, I think the bulb is connected wrong.

hmmm...ignition off and parking lights on; which bulb/light should light up? it's very possible the bulb wires are mixed up...

[Mike Bellis]

There is a dash light that illuminates with the parking lamps. White/Blue or White Green, I think. Make sure your dash lamps are connected correctly. If the alt light goes on with parking lamps and off with head lamps, I think the bulb is connected wrong.

hmmm...ignition off and parking lights on; which bulb/light should light up? it's very possible the bulb wires are mixed up...

If I remember correctly, there is a lamp at the 7 o'clock position in the tach or speedo for the parking lamps. I may be wrong with the location, I run Autometer gauges now. Take the 6 screws from the gauge cluster and pop it out. you should see the wire I mention somewhere.

[realred914]

There is a dash light that illuminates with the parking lamps. White/Blue or White Green, I think. Make sure your dash lamps are connected correctly. If the alt light goes on with parking lamps and off with head lamps, I think the bulb is connected wrong.

hmmm...ignition off and parking lights on; which bulb/light should light up? it's very possible the bulb wires are mixed up...

green lamp, on speedo I believe down near teh botom of this, six o clokc popstion that be the parking light on indicator