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BJ8 Tachometer and Fuel gauge stopped working.

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G'day all,

Despite the car working perfectly well, the tachometer and fuel gauge have stopped working. On the tacho the ignition light still operates as it should but the needle refuses to move.

Similarly, the fuel gauge has also ceased to make any effort at all to indicate the level of fuel, which is dreadfully rude I'm sure you'll agree.

All other instruments are fine and perfectly operational.

I'm a little confused. Actually I'm flummoxed. The cables at the back look alright.....under the hood what should I be looking for? What does the tacho connect to?

Tried to get into the fuse box to have a look but couldn't get the lid off and didn't want to snap anything. What's the technique?

I appreciate any assistance and advice that you might be able to give me.

Thanks

Bobby
 

saltiga

Senior Member
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Hello, Freshman I also live in Australia I can be contacted by E/mail trevor9@esc.net.au Look at the wireing diag and the fault you have is linked together,item 19 is the fuse block, a feed wire goes from this to item34 which is the fuel gauge, it distributes to the fuel sender item35 activating the fuel gauge needle , a wire that is common to the wire from the fuse block goes to the tacho(in common) this indicates to me that there is a problem with the wire from item 19 to item34, maybe a dirty terminal, Regards Trevor Short
 

SpacerM

Senior Member
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Did you check that behind the dash for loose/disconnected wires? If everything is plugged in, it very likely its simply a blown or poorly connected fuse. The Fuse box cover on the BJ8 simply lifts off (the fuse box is mounted on the engine-side of the firewall right in front of the driver on LHD cars)- be sure you are working on the fuse box and not the regulator or some other piece of equipment. The cover pulls straight off:
FUSE500.jpg


Even if the fuse doesn't loook blown replace it, clean all the contracts with sandpaper and push the clips closer together. If that doesn't work you can start troubleshooting the wires Trevor mentioned, and don't forget to check your grounds behind the dash.
 
OP
T
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Hi guys

Update after 2.5 years.....it was a blown fuse (35A). Replaced it; no issues......until the other day when it happened again.....only this time when I replaced the blown fuse it immediately blew within 2 mins of driving. I realised I'd only replaced it with a 30A fuse so went to pick up some 35A fuses (as per the workbook) and again it blew within a few hundred metres of driving.

So, I think this means there's a short somewhere. Good old Prince of Darkness eh.

A few questions as I'm not electrically-minded I'm afraid:

1. Would a 'short' most likely be a bit of exposed wire touching the chassis (or anything else metallic, or could it also be within the loom itself e.g. exposed wire touching another piece of exposed wire? Is this likely to happen?
2. Where would be the best place to start to try and find the offending short circuit....the instruments or the battery?
3. Any tips or tricks for what to look out for?

As ever, advice is greatly appreciated.

Regards

Rob
 

Keoke

Great Pumpkin
Country flag
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Well Saltiga gave some good places to check.

Yes you could have a short, however, if that 35 Amp fuse was a British fuse you replaced in the car:

It was under rated.

Try a british 50 Amp fuse or an American standard AGC 30Amp .
 

RAC68

Darth Vader
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Hi All,

You definitely have a short and be very careful that you follow Keode's fuse suggestion as your British 35 is approximately equivalent to a US AGC 17, and I suggest installing a much smaller testing fuse to lower the risk of melting wire insulation within the harness and causing a major problem. Also, since the failing fuse also covers a few other components (i.e. wipers, etc), suggest disconnecting the green 2-wire connector at the fuel gauge along with the 1-wire connector at the tachometer(temporarily wrap with tape) and check to see of the fault in isolated to this specific circuit. However, check the green 2-wire connection at the fuel gauge as Trevor suggested and make sure it is firmly plugged in and not touching the body or gauge mounts.

All the best,
Ray(64BJ8P1)
 
OP
T
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Thanks chaps

The fuses I've replaced the original Lucas one with have been Australian. Not sure if they're the same standard or if they're a bit weaker as you suggest the British ones are.

Is it worth buying a powered test light and trying to find the short with battery and fuse disconnected, or is there an easier way?
 

RAC68

Darth Vader
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Is it worth buying a powered test light and trying to find the short with battery and fuse disconnected, or is there an easier way?


I prefer an inexpensive multi-meter with leads modified to extend its range and versatility. You can get one for a little more money then the test light but it has much more versatility. However, although I would like to help in an appropriate way, it would help to know your Healey (British car) maintenance experience and if you have a wiring diagram for your car?

So that we are all on the same page, I suggest you go to (https://www.vintage-sportscar-touring.ca/pdf/BJ8wire.pdf) and download the diagram.

Hope this helped,
Ray(64BJ8P1)
 
OP
T
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Thanks Ray

Maintenance experience minimal to be honest....but keen to have a go. Wiring diagram downloaded.

The part I'm struggling with is the theory. There are only two fuses and the one that keeps blowing is supposed to be the fuse for all manner of things, according to the diagram, such as the overdrive relay, turn flasher, wiper motor and so on - but those things all work; it's just the tachometer and fuel gauge that don't.

In practical terms, I'd like to work out the best way to find the short that it obviously causing the issues here. What's the best way using a multimeter? I have one at home but have only ever used it to test voltage on my Land Rover second battery so I'm by no means highly familiar with how it works or how to best use it.
 

Keoke

Great Pumpkin
Country flag
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The time delay of your replaced fuse failure suggests it is underrated.??
 

John Turney

Yoda
Silver
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...
The part I'm struggling with is the theory. There are only two fuses and the one that keeps blowing is supposed to be the fuse for all manner of things, according to the diagram, such as the overdrive relay, turn flasher, wiper motor and so on - but those things all work; it's just the tachometer and fuel gauge that don't.

....
That tells me your car isn't wired like the diagram, although the overdrive relay should be wired before the fuse and would be unfused.

The short is unlikely to be within the harness unless the outer cloth sheath of the harness is worn through. It's more likely at the connections or in the instruments. If you had a "dead short", the fuse would blow immediately and not minutes later.

There are a couple of ways to use a multimeter to look for a short. The multimeter has the ability to measure resistance. Where I would start is to shut off all electrical power by turning the Master Switch in the trunk ("bat kill" on the diagram) off or disconnecting the batter cable from ground.

Then, disconnect the green wires from the "B" terminal of the fuel gauge. Measure the resistance between the "B" terminal to ground. It should be at least 10 ohms (it varies with tank level - at least in theory).

Then measure the resistance between the disconnected green wire ends and ground. It may read a very low resistance or infinite. Either is ok, but if it reads infinite, you know the short is not in the wire to the fuel gauge. If it reads a low resistance, you will need to find out which green wire at terminal 4 of the fuse box is the wire to the fuel gauge. Leave the green wire disconnected from the fuel gauge. Do that by disconnecting the green wires at the fuse box and individually measuring the resistance between the green wire end at the fuel gauge and each green wire end at the fuse box. The one with almost zero resistance is the same wire. The others should read infinite resistance (or almost). With the green wire disconnected from the fuse box, now measure the resistance from the wire end to ground. Again, it should read about 10 ohms, or more, because you are still connected to the tachometer.

Then disconnect the green wire from the tachometer and measure the resistance from the tachometer terminal to ground. Again, it should read about 10 ohms, or more. Now measure the resistance from the end of the green wire to ground. Since you have all three ends of the green wire disconnected, it should have infinite resistance to ground. If not, your short is in the wire.
 
OP
T
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UPDATE

I have previously provided incorrect information....so please accept my apologies if I got you guys scratching your heads unnecessarily.

With the fuse blown, it's not just the tachometer and fuel gauge that aren't working.....the wipers, indicators and brake lights aren't either....which is correct according to the wiring diagram.

I'm still unsure how to find the problem but this isn't helped by the fact that I put in a fuse I had in the garage just to test this and now everything is working. Engine wasn't running though....and typically this is the case until I fire her up and then leave the driveway......it's after a minute or sometimes just a few seconds that the fuse blows.
 

Keoke

Great Pumpkin
Country flag
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I have previously provided incorrect information.
WOT!!------:highly_amused:

Take a spin around the block and see what happens.??
If the fuse blows :
This is easier to troubleshoot.
 

John Turney

Yoda
Silver
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UPDATE

I have previously provided incorrect information....so please accept my apologies if I got you guys scratching your heads unnecessarily.

With the fuse blown, it's not just the tachometer and fuel gauge that aren't working.....the wipers, indicators and brake lights aren't either....which is correct according to the wiring diagram.

I'm still unsure how to find the problem but this isn't helped by the fact that I put in a fuse I had in the garage just to test this and now everything is working. Engine wasn't running though....and typically this is the case until I fire her up and then leave the driveway......it's after a minute or sometimes just a few seconds that the fuse blows.

Well, that does make a bit of a difference.

You may want to disconnect and label all those green wires from the fuse box. Then hook them back up one at a time, until you find the one that causes the fuse to blow.
 

Bob Hughes

Luke Skywalker
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I am with John Turney on that one- that was how I found out that my windscreen wiper motor was the cause of my problem - the carbon brushes were worn right through to the brush holders and the armature was worn to a frazzle - nasty.

:cheers:

Bob
 
OP
T
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Yes, I know, I'm terrible....sorry chaps.

Ray has been helping me with some tips on diagnosing this.....and the other day I put a new 35A fuse in and managed about 7kms before it blew when I turned into the auto parts store car park. This is what has me thinking it's either brake lights or indicators - but then they worked before that as I had to make right and left turns, braking at both intersections and no issues.

So, I figure that I need to replicate the conditions and as you guys and Ray have suggested, disconnect everything and then put them back one at a time and drive until something blows!


Now this could take a while and to be honest I don't really like driving without brakes or indicators so if there is a safer way of doing this I'd be keen to hear it.
 

Keoke

Great Pumpkin
Country flag
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Well I don't really like driving without brakes or indicators so if there is a safer way of doing this??

Well Ole Chap:
Disconnect all the circuits except the brakes and indicators and give it a go??
Then reconnect the remaining wires one at a time and retest until you replicate the failure if it did not reoccur with brakes & indicators only..
 

John Turney

Yoda
Silver
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If your multimeter can handle 30+ amps, you could disconnect all those green wires form the fuse box (labeling them) and try each item while measuring the current from the fusebox to each wire with the multimeter. Have someone activate each of the circuits while you measure.
 

BJ8Healeys

Jedi Warrior
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What I did, but then I drive my car a lot:
Separate all those five circuits into fuses of their own. I started losing fuel gauge, tachometer, etc. on the way to Conclave in Cleveland in 2006. I went through a box of fuses before I found the problem circuit because the fuse didn't blow immediately in each case. Someone had given me an extra fuse box with four slots in a stash of parts, so I located it under the dash and connected the fuel gauge/tach, wipers, turn signals, and brake light each to its own labeled fuse and left the heater blower fuse in the original location.

A few years later, my turn signals quit and it was easy to see that fuse had blown and avoid troubleshooting all the other circuits. Problem was a pinched/chafed wire in the steering column harness.
 
OP
T
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Ok this sounds interesting......because I recently had someone replace a rocker for me and the day I picked up the car I noticed that the steering wheel had been pulled right back i.e. at its furthest extension, and tightened too. I got it back to where I normally have it but perhaps this could be the issue - indicator wire in the column.

I'll still troubleshoot it the normal way but will keep this in mind.

Was that hard to fix, Steve?

Bobby
 
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