Weird Electrical problem/symptom!
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,154
Likes: 271
From: Dunedin NZ.
Weird Electrical problem/symptom!
I was reconnecting the accelerator cable to the carb and as the cable touched the carb there was a spark generated. The key was off so no current should have been flowing anywhere except for the clock etc. What would cause this? The chassis earth to the engine block is clean and sound so why would any current flow through the acc cable anyway?
According to the ammeter the charging system is working but I notice that the needle flicks from 0 amps to say 3 amps when the car is running with the lights off as if the charge regulator is flicking in and out, is this normal for a 70 C3? (The battery is nearly new so would be fully charged). Could it be a grounding issue for say the clock (its not working). The lights are all working normally.
According to the ammeter the charging system is working but I notice that the needle flicks from 0 amps to say 3 amps when the car is running with the lights off as if the charge regulator is flicking in and out, is this normal for a 70 C3? (The battery is nearly new so would be fully charged). Could it be a grounding issue for say the clock (its not working). The lights are all working normally.
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,154
Likes: 271
From: Dunedin NZ.
No Electric choke fitted to this carb, not static charge as I have now measured it at 8.8 Volts and yes it sparks every time I touch the inner cable to the carb or any other "ground" on the engine. Voltage present but cant seem to get any current reading.
So, the cable is acting as a wire because the inner core is insulated from the outer sheath by but what would cause the electrical potential of the gas pedal assembly to be higher than the engine? Can anyone tell me if the gas pedal mounting is earthed to the frame or is it insulated by the firewall its bolted to? I assume the firewall is all fibreglass? Perhaps there is a bonding wire missing behind the dash somewhere?
So, the cable is acting as a wire because the inner core is insulated from the outer sheath by but what would cause the electrical potential of the gas pedal assembly to be higher than the engine? Can anyone tell me if the gas pedal mounting is earthed to the frame or is it insulated by the firewall its bolted to? I assume the firewall is all fibreglass? Perhaps there is a bonding wire missing behind the dash somewhere?
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,154
Likes: 271
From: Dunedin NZ.
Hmm, could it be I have this around the wrong way and it is because the gas pedal assy is insulated from any ground except when the cable is connected. When I touch the cable to the carb it becomes the same potential as the carb/ engine etc. Still thinking I am "short" of a bonding wire.
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Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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Could be a bad diode in the alternator.
Remove the battery cable from the alternator, test again and see if the short is eliminated.
Remove the battery cable from the alternator, test again and see if the short is eliminated.
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,154
Likes: 271
From: Dunedin NZ.
Yes wipers and fan work, no I haven't touched the starter but occasionally it will just click and not turn the motor over, I will check all of the starter connections, this was on my to do list anyway. I will try removing the batt cable from the alternator first though, thanks for your suggestions everyone.
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
So much for an easy fix!
Here's your basic starter connections, not shown is a black wire that is the ground for the wiper and fan motor. It connects to a starter or bell housing bolt.
If that's good you might connect your meter between the cable and a ground and pull each fuse one at a time. If the draw goes away then you have narrowed the problem to one circuit.
Schematic:
http://www.vetteprojects.com/bmv/mis...70%20Early.pdf
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Most often, you can't actually see static discharge in daylight. If you see a yellow/white spark each time you make contact as you've described, it's not just a static charge. Check voltage between the two parts you are putting together (when they are still separated). If it has voltage (is that the 8.8 vdc measurement you made?), a 12vdc signal is leaking into the positive charged component.
Team Owner
Joined: Jul 1999
Posts: 65,492
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From: Orange Park Florida
Three thing to check.....the negative cable from the battery to your frame just under the bat box....make damn sure that frame is clean pure steel and not rust, and that the cable is clean also.....use RTV to redo the connection with, as you torque down the bolt it will ooze out and allow a 100% connection....and if you cover it over the entire joint there is a permanent water proof seal on that cable.....
now to look under the pass side engine mount, up under the shell of the mount horn you find a cable from the engine block, most likely from the engine mount, treat the connections in a similar fashion.....
if you find anything shaky or corroded looking, replace the cables from your parts house.....copper wire corrodes green looking, the more green the worse....and it does not get along well with steel....so you need to make sure there is no oxygen getting to the connection once it is secured....
now to look under the pass side engine mount, up under the shell of the mount horn you find a cable from the engine block, most likely from the engine mount, treat the connections in a similar fashion.....
if you find anything shaky or corroded looking, replace the cables from your parts house.....copper wire corrodes green looking, the more green the worse....and it does not get along well with steel....so you need to make sure there is no oxygen getting to the connection once it is secured....
Thread Starter
Melting Slicks
Joined: Oct 2012
Posts: 2,154
Likes: 271
From: Dunedin NZ.
Hmm, I connected a 12v test light between the acc cable and earth and it would not light up indicating that there is very little current flowing? But the spark is still there when you touch the cable to earth. One thing I didn't notice before though that is when you do this the warning LED for the burglar alarm flashes several times and then stops (this is with the alarm not set, I haven't tried that as the missus is asleep)! Still have yet to try removing the the fuses one at a time to see if the spark stops.
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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