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#26 Rockoz

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Posted 25 August 2023 - 03:42 PM

You missed the most important part. You MUST have a wire from the - terminal of the battery to the body. This is the 0V reference (and return) for all of the electrical loads on the body. The big one to the engine is only for the starter, coil and other engine mounted solenoids or items that need a 0V reference to work like temperature sensor.
Remember the engine& box is connected to the body via rubber. The exhaust and diff are connected to the body via rubber. About the only body to engine metallic connections are things like choke cable metal sheath or throttle linkage on early cars like HK-HG. Which is why things go haywire without the original 0V connection in place.

 

Using 0V is technically correct as we both know.

But for the sake of clarity for those with limited electrical knowledge I think we should keep using negative, ground and or earth.

It makes it simpler for those trying to work it all out.

 

But seriously guys. Ive posted about it quite a few times.

If you are going to play with the wiring, please go buy a multimeter.

It makes life easier for you, and when you need help it makes it easier for the person with knowledge to give you the right advice.

And if given a set of things to measure with the multimeter, do those, nothing else, and sometimes even the order of the tests makes a difference.

 

Jaycar sell a reasonably priced multimeter that also has a clamp ammeter on it which will measure DC Amps.

Last I looked it was well under a hundred bucks.

It could mean the difference between spending days chasing a problem or just an hour or so.

 

Cheers

 

Rob



#27 claysummers

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Posted 25 August 2023 - 05:14 PM

The early cars pre-HK had a braided fuel hose from the yard line to fuel pump which was the factory body earth. People would cut or discard it in order to fit an inline plastic filter and woder why they started having earthing issues. Gears in the box apparently would suffer due to current finding a path through them.

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#28 yel327

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Posted 25 August 2023 - 05:14 PM

I'm the other way Rob, I think the correct terms should be used. With the proliferation of vehicle mounted inverters and portable 240V alternators (often called generators) today it is extremely important that people understand that EARTH is almost always not applicable to a vehicle, GROUND not quite as bad but it is still not correct. These terms are for power systems, including the EARTH pin of an inverter or alternator/generator output. A vehicle chassis is sometimes called chassis ground but in reality, it is 0V of a 12V system.

 

None of that matters though, and Rob is 100% correct on chasing wiring. Just don't use the Jaycar multimeter on Low Voltage - keep it exclusively for Extra Low Voltage (less than 120Vdc or 50Vac). They are not safe for use on 240/415V or similar AC power systems even if they say they are. They might be OK for low fault level equipment like inverter outputs but you are risking your life using them on a mains/grid fed Low Voltage system. Even with a lower end 3-4kA fault level that is enough to badly damage your hands, face or airway if the meter lets go inside. The DC hall effect measurement feature is a great thing too for automotive use. This one below is one of my favourites as they are reasonably cheap, have an open end hall effect measurement CT for DC current and have leads and probes and body rated to CAT IV 600V so won't snot itself in your hand when used on power systems.

 

https://www.ebay.com...kp:BFBM3uy-uMVi

 

One way to test is grab a jumper lead, clamp it to the battery - terminal and the other end to exposed steel. Then see if the issues go away.



#29 Bruiser

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Posted 25 August 2023 - 06:06 PM

Hi nanbar,
Just wondering, were your fuel gauge and tacho both working properly before?
Do the headlights work ok?
I can’t help wondering if the tacho +ve feed is on the wrong terminal on your light switch maybe
seeing as the dash dimmer switch effects it.
The fuel gauge earth is actually the metal body of the sender attached to the tank, which earths to the body
through the tank, related to what the guys have said already.
Like yel just described, a wire (or jumper lead) attached to one of the sender screws run to the body would make a new
earth which would eliminate that as a possible fault.
As long as the body and engine earths are in good nick.
You can give the wire lug, bolt/screw and the surface it attaches to a polish up with fine sandpaper to
be sure of a good electrical contact

#30 Bruiser

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Posted 25 August 2023 - 06:09 PM

One for you electrical blokes, why would the tach work ok until the lights are switched on?

#31 yel327

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Posted 25 August 2023 - 06:21 PM

Body not connected to the battery -ve terminal.



#32 Bruiser

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Posted 25 August 2023 - 06:23 PM

Why would it work at all then?
Unless tach -ve goes direct to battery?

#33 nanbar

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Posted 25 August 2023 - 06:41 PM

I'm the other way Rob, I think the correct terms should be used. With the proliferation of vehicle mounted inverters and portable 240V alternators (often called generators) today it is extremely important that people understand that EARTH is almost always not applicable to a vehicle, GROUND not quite as bad but it is still not correct. These terms are for power systems, including the EARTH pin of an inverter or alternator/generator output. A vehicle chassis is sometimes called chassis ground but in reality, it is 0V of a 12V system.

 

None of that matters though, and Rob is 100% correct on chasing wiring. Just don't use the Jaycar multimeter on Low Voltage - keep it exclusively for Extra Low Voltage (less than 120Vdc or 50Vac). They are not safe for use on 240/415V or similar AC power systems even if they say they are. They might be OK for low fault level equipment like inverter outputs but you are risking your life using them on a mains/grid fed Low Voltage system. Even with a lower end 3-4kA fault level that is enough to badly damage your hands, face or airway if the meter lets go inside. The DC hall effect measurement feature is a great thing too for automotive use. This one below is one of my favourites as they are reasonably cheap, have an open end hall effect measurement CT for DC current and have leads and probes and body rated to CAT IV 600V so won't snot itself in your hand when used on power systems.

 

https://www.ebay.com...kp:BFBM3uy-uMVi

 

One way to test is grab a jumper lead, clamp it to the battery - terminal and the other end to exposed steel. Then see if the issues go away.

I connected one end of a jumper lead to the negative terminal on the battery and the other end to a bolt through the boot floor. I repeated the test by clamping the lead to the chassis rail making sure it was clean and free of paint. On both occasions, I started the car, the tacho was working with the lights off, I turn the lights on and the tacho went to zero. I un-dimmed the dash lights and the tacho started working.

Earlier today, I ran both the headlight earths temporarily but securely) to the top radiator bolt, problem with tacho/lights on still existed.

I also put a multimeter across the negative terminal on the battery and the body, it read zero volts on numerous places.

It seems to me to be related to the dimmer switch on the light and the wire.

Below is a picture of the back of the dash, you can see the ball of the tacho (non standard), I wonder if the one of the wire which picks up power is connected to the dash light cricuit thus affecting its operation. The tacho has four wires, red white green and black. The black wire is cut in half. I rejoined it and it made no difference to the problem but I am not sure about it. I need to figure out what the wires are and where they go, I assume these wires are standard for a tacho?

Attached Files


Edited by nanbar, 25 August 2023 - 06:49 PM.


#34 Bruiser

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Posted 25 August 2023 - 06:52 PM

If that black number is the tach, what’s going on with it’s black wire heading out bottom of shot?
Looks to be taped up, and also maybe broken at the point just below the bucket there
Also the earth lug bottom left - temp gauge? Has a taped up black wire hanging there
Is the black wire from the tach connected to anything?

#35 nanbar

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Posted 25 August 2023 - 07:07 PM

If that black number is the tach, what’s going on with it’s black wire heading out bottom of shot?
Looks to be taped up, and also maybe broken at the point just below the bucket there
Also the earth lug bottom left - temp gauge? Has a taped up black wire hanging there
Is the black wire from the tach connected to anything?

The black wire from the tacho was cut, I joined it and it made no difference so I figured it may have been cut for a reason so I unjoined it and taped the ends. I didn't bother to look properly but your observant eye has noticed its the tach wire I taped. Is that the earth wire?



#36 Bruiser

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Posted 25 August 2023 - 07:35 PM

Looks like the typical red white green black wire setup. Black is the -ve ground.
Connect it up, and have a good look at the bit that looks broken to be sure
That might be why there was no difference when you tried joining it
Red is +ve feed
Green is tach signal from coil
White is for the light bulb inside connected to the other dash bulbs

#37 nanbar

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Posted 25 August 2023 - 07:56 PM

Looks like the typical red white green black wire setup. Black is the -ve ground.
Connect it up, and have a good look at the bit that looks broken to be sure
That might be why there was no difference when you tried joining it
Red is +ve feed
Green is tach signal from coil
White is for the light bulb inside connected to the other dash bulbs

Thankyou so much for your help, it is very much appreciated.

Ill definitely reconnect the black and double hail it.

Red looks like is piggy backed off the fuel gauge power, is this ok?

Green I assume is good.

White I need to check, I wonder if the tacho is dim compatible?

The tomorrows job.


Edited by nanbar, 25 August 2023 - 07:58 PM.


#38 yel327

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Posted 25 August 2023 - 08:43 PM

I connected one end of a jumper lead to the negative terminal on the battery and the other end to a bolt through the boot floor. I repeated the test by clamping the lead to the chassis rail making sure it was clean and free of paint. On both occasions, I started the car, the tacho was working with the lights off, I turn the lights on and the tacho went to zero. I un-dimmed the dash lights and the tacho started working.
Earlier today, I ran both the headlight earths temporarily but securely) to the top radiator bolt, problem with tacho/lights on still existed.
I also put a multimeter across the negative terminal on the battery and the body, it read zero volts on numerous places.
It seems to me to be related to the dimmer switch on the light and the wire.
Below is a picture of the back of the dash, you can see the ball of the tacho (non standard), I wonder if the one of the wire which picks up power is connected to the dash light cricuit thus affecting its operation. The tacho has four wires, red white green and black. The black wire is cut in half. I rejoined it and it made no difference to the problem but I am not sure about it. I need to figure out what the wires are and where they go, I assume these wires are standard for a tacho?


It still sounds like an equipotential problem as in all of the body is at the same potential as the battery -ve or there is a 12V feed issue. Probably around the dash but it could be the engine area too. Hard to diagnose from a distance.

#39 yel327

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Posted 25 August 2023 - 08:56 PM

What it sounds like is the potential of a metal part of the car (or even a wiring joint) somewhere is floating and when you are running current through something (like the dash lights) the resistance balance is causing a voltage rise on that metal part. It’s hard to explain without drawing a picture. If the wiring you have played with isn’t the culprit, try the same trick with the jumper lead from the metal dash frame to a clean part of the body steel or if it’ll reach to the battery - terminal. Just to rule out a floating dash body, as in not properly connected to the -ve terminal.

Edited by yel327, 25 August 2023 - 08:57 PM.


#40 Bruiser

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Posted 25 August 2023 - 09:13 PM

Yel, could it be that the tach innards are finding an earth back through the common earth it shares with it’s own light bulb,
on through the white wire, which sees the track through the other dash bulbs as an earth?
When the dash lights come on, that earth becomes +12v
Like indicators and brake lights going bonkers through each other when one of their earths fails

#41 nanbar

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Posted 26 August 2023 - 07:00 AM

Yel, could it be that the tach innards are finding an earth back through the common earth it shares with it’s own light bulb,
on through the white wire, which sees the track through the other dash bulbs as an earth?
When the dash lights come on, that earth becomes +12v
Like indicators and brake lights going bonkers through each other when one of their earths fails

Check this picture out. I took it the other night of each gauge to email to a gauge place to get a quote on a refurb.

The engine was running at the lights were on.

Fuel gauge was working, oil pressure was up, tacho and volts (which are connect via power and earth) were at zero!

Attached Files



#42 S pack

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Posted 26 August 2023 - 07:49 AM

I see two errors in your wiring. Your tach and volt meter are grounded to the back of the instrument panel but the panel is not grounded to the body.

The GREY wire coming from the main instrument harness which you have connected to the back of the instrument panel is not a -ve, it is 12v+ for the instrument lighting.

Your tach and volt meter are grounding back through the lighting switch when the lighting system is turned off.



#43 yel327

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Posted 26 August 2023 - 08:03 AM

Yel, could it be that the tach innards are finding an earth back through the common earth it shares with it’s own light bulb,
on through the white wire, which sees the track through the other dash bulbs as an earth?
When the dash lights come on, that earth becomes +12v
Like indicators and brake lights going bonkers through each other when one of their earths fails

 

That is essentially what I was saying. A floating common, in this case the dash metal back. I think Dave nailed the problem above though.



#44 S pack

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Posted 26 August 2023 - 08:14 AM

I see two errors in your wiring. Your tach and volt meter are grounded to the back of the instrument panel but the panel is not grounded to the body.

The GREY wire coming from the main instrument harness which you have connected to the back of the instrument panel is not a -ve, it is 12v+ for the instrument lighting.

Your tach and volt meter are grounding back through the lighting switch when the lighting system is turned off.

Actually just looking at the pic again and the tach -ve black wire isn't connected to the black -ve from the volt meter. The -ve from the tach drops down out of view at the bottom of the pic. So what does the tach -ve connect to?

The other black -ve wire connecting to the ring connector with the volt meter -ve appears to be grounding the instrument panel bulb between the tach & speedo.

Best thing to do with that instrument wiring is rip it all out and start again.
 


Edited by S pack, 26 August 2023 - 08:15 AM.


#45 nanbar

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Posted 26 August 2023 - 09:41 AM

I think I have fixed it. I properly connected the ground from the tacho. I tidied up all the loose connections and covered any bare wire with insulating or heat shrink where I could.

with the dash out, I ran an earth wire from the one of the factory dash earths to the screw which holds the dash in. It all seems to work properly now. I put the gauges cluster panel back in without the temp earth wire connected and still seems to work. 



#46 nanbar

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Posted 26 August 2023 - 12:44 PM

PS Thanks to everyone for all your help with all the problem solving ideas and instructions.



#47 Bruiser

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Posted 26 August 2023 - 05:35 PM

Nice one mate

#48 Rockoz

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Posted 26 August 2023 - 07:54 PM

But seriously a multimeter would have helped get you sorted quicker.

Byron is exactly right in what he says though.

I try to make it less complicated.

If you want to play with electrical please buy a multimeter.
It makes the job of the blokes that know so much easier.

And you will get a quicker result.

 

Ive given detailed instructions to forum members with basic checks.

They have decided to do other checks on the initiation of other members, not this forum specifically.

 

I spent 9 days once with a forum member sorting out a problem

If he had have listened to only me, the problem would have been fixed in hours.

Byron has a different approach, but the same result would have happened.

 

Cheers 

 

Rob



#49 yel327

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Posted 26 August 2023 - 09:08 PM

Can’t agree with you more Rob, buy a multimeter. And unless it’s a Fluke or similar quality use it only on the car.

Just make sure what you buy does DC current, have a look at this one, there is a table in the photos that show you the DC current model:

https://www.ebay.com...kp:BFBMqOKdmMZi

Just don’t use it on 240/415V!

I’d buy one of these though:

https://www.ebay.com...:Bk9SR8as2pjGYg

Edited by yel327, 26 August 2023 - 09:14 PM.


#50 yel327

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Posted 26 August 2023 - 09:22 PM

I might be wrong about those new T5-1000. They only have AC current. I thought they were DC. This copy says it is:
https://www.ebay.com...:Bk9SR8as2pjGYg

I’m sure my old T5 was DC current.




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