Weird electrics problems getting weirder

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David Jones
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Re: Weird electrics problems getting weirder

#31 Post by David Jones » Mon Aug 12, 2019 8:56 am

Joseph Lucas may have invented darkness but Robert Bosch improved on it.
If I had known I would live this long I would have pushed the envelope a little harder.
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Re: Weird electrics problems getting weirder

#32 Post by david pettengell » Mon Aug 12, 2019 9:42 am

neilbardsley wrote:
Wed Aug 07, 2019 7:16 am
David there is a very good 356b owner and electrician on DDK. Based near Worcester : Winston. Top bloke. Call him and he will be able to help. I believe that RPL maybe do a blade fuse box but I suspect that isn't your issue.

VEHICLE WIRING SERVICES (WINSTON TEAGUE/DAVID ASTON)
Address: Worcestershire
Phone: Winston Teague 07971 415277, David Aston 07968 225262
Email: vehiclewiring@googlemail.com
Website: www.vehiclewiringservices.co.uk
Services: Specialist historic and vintage vehicle electricians. Bespoke wiring harnesses designed, manufactured, fitted and commissioned.
Neil, you wouldn't have any other contact info would you? I have left voicemails on both numbers and sent an email with no response?

Dave

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Re: Weird electrics problems getting weirder

#33 Post by Greg Bryan » Mon Aug 12, 2019 1:09 pm

David - I don’t envy you chasing an electrical gremlin - can be very frustrating
While grounds are equally import to power supply, you have to pay attention to both. I would use a jumper wire and go from the #30 terminal (big red wire always hot) on the ignition switch and hook it to the instrument wire (small blue with yellow) and see if that improves the situation. Also, check to see if someone has powered an electric tach off of the instrument power wire. If they have, temporarily disconnect it to see if the problem improves.
You can also hook a jumper wire to the instrument case and ground to be doubly sure you have a perfect ground
If the instrument continues to be erratic with this config, maybe the problem is in one of the gauge circuits - you can also disconnect them one at a time to isolate the problem
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Re: Weird electrics problems getting weirder

#34 Post by C J Murray » Mon Aug 12, 2019 1:43 pm

Greg is right on! Electrical problems are solved using a process of elimination and jumper wires are very useful at isolating suspected faults.
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Re: Weird electrics problems getting weirder

#35 Post by david pettengell » Mon Aug 12, 2019 1:53 pm

Interesting. I put in an electric tach and I am pretty sure I powered it from the instrument power wire so I will check that. Thanks for the tips

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Re: Weird electrics problems getting weirder

#36 Post by neilbardsley » Mon Aug 12, 2019 5:48 pm

david pettengell wrote:
Mon Aug 12, 2019 9:42 am
neilbardsley wrote:
Wed Aug 07, 2019 7:16 am
David there is a very good 356b owner and electrician on DDK. Based near Worcester : Winston. Top bloke. Call him and he will be able to help. I believe that RPL maybe do a blade fuse box but I suspect that isn't your issue.

VEHICLE WIRING SERVICES (WINSTON TEAGUE/DAVID ASTON)
Address: Worcestershire
Phone: Winston Teague 07971 415277, David Aston 07968 225262
Email: vehiclewiring@googlemail.com
Website: www.vehiclewiringservices.co.uk
Services: Specialist historic and vintage vehicle electricians. Bespoke wiring harnesses designed, manufactured, fitted and commissioned.
Neil, you wouldn't have any other contact info would you? I have left voicemails on both numbers and sent an email with no response?

Dave
Those have worked for me in the past. Winston posted on Saturday on DDK so I've sent him an message

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Re: Weird electrics problems getting weirder

#37 Post by Juha Vane » Tue Aug 13, 2019 1:45 am

Just a little “trick”, troubleshooting electrical problems that
occasionally burn fuses can be hard to find. Make a “fuse” of
a 6/12V bulb and use it in instead of the fuse. When the circuit
get grounded, the fuse-lamp will lit and now you can wiggle the
wires or do whatever to find where the problem is hiding.
KTF,

Juha Vane
Finland

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Re: Weird electrics problems getting weirder

#38 Post by david pettengell » Tue Aug 13, 2019 4:36 am

Thanks for the advice and thanks Neil, Winston contacted me because you messaged!!

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Re: Weird electrics problems getting weirder

#39 Post by david pettengell » Thu Aug 15, 2019 10:38 am

So, I spoke to Winston, lovely man, very helpful but this isn't really the type of work they do and they are full booked for a while.

So, it's back to me trying to fix it. So my plan for next weekend is test every ground is below 5 ohms again. Remove the unusual ground wire that runs from battery to the starter that shouldn't be there. Remove the positive feed from the electric tacho I put in and test again. Any other thoughts?

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Re: Weird electrics problems getting weirder

#40 Post by David Jones » Thu Aug 15, 2019 11:23 am

David, I am convinced it is a ground problem because it is the common denominator and you have more than one issue. Turn on the headlights and measure the voltage at the headlight itself. You will have to remove the headlight to do this of course but you can then check for volts drop under load and then by elimination move back up the line so to speak and find where the volts drop is occurring and hopefully find the earth problem. What you appear to have is a problem called a parallel earth where the path to ground keeps switching depending on what circuit is in use. Some circuits are always in use such as ignition and gauges as soon as the ignition is turned on. Sometime you can pinpoint the suspect part of the circuit by deduction from the circuits that disrupt the gauges. It is just a logic exercise but sometimes one cannot see the forest because of the trees.
Running a jumper wire from the battery negative to the back of the dash is still top of my list to help diagnose where the problem lies.
If I had known I would live this long I would have pushed the envelope a little harder.
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Re: Weird electrics problems getting weirder

#41 Post by david pettengell » Thu Aug 15, 2019 11:40 am

Thanks David, I will do the jump wire first

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Re: Weird electrics problems getting weirder

#42 Post by david pettengell » Sun Aug 25, 2019 5:03 pm

So, got some time on the car today. Tried the jump wire and it resolved some of the issue, went on to test the ground at the gauge and it was showing over 50ohms resistance for ground. So, I ran a new ground wire to the gauge and it is much more stable. Shows correct readings for oil temp and fuel gauge BUT is still jumping furiously when I switch on the indicators. I tightened all the connections at the fuse box but nothing improved.

Any ideas what to check next? I also checked the ground of the engine and it was showing 0.9 ohms so it seems the engine is grounding well.

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Re: Weird electrics problems getting weirder

#43 Post by David Jones » Sun Aug 25, 2019 5:26 pm

Try a separate ground for the indicators. There should be a grounding strap on all indicators on A cars. You may have a grounding track through the gauge.
If I had known I would live this long I would have pushed the envelope a little harder.
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