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Earthing cockup (part 2)


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Gents, since a few weeks i'm dealing with strange electrical gremlins: intermittent spark failure which i though being the coil, then condenser, then points, then leads, then rotor arm, etc... Ignition would stop working for a few hours then start again. When i'll put a test lamp on the (+) of the coil...the electric fan would kick in... Then i tried installing a 2-speed wiper motor supplied by AlanT and I got 12 V on both green-brown and green-red with the green connected to 12 V.... Then today, few bangs-black-smoke-bang and the engine died on the highway. Two cops came to rescue, 1 holding the spanners and the other one holding an umbrella while i was swapping the coil. And it cranked ok and off i went until home, no problem. Stopped in the drive and few hours after I tried to crank again... no way to get the engine to fire, no sparks. Swapped the coil again, checked the leads, points, etc... No sparks at the plugs. Per accident I finally discovered something strange: When i connect one end of the test lamp on the battery earth terminal (-), undo the quick disconnect and touch the other end of the lamp on any earth of the body (-) the bulb will set off... so that means that the car body is (+) and (-) whenever it feels like it !!! (see pic) Obviously there's something amiss. I'm nearly positive these problems have one single cause: resistance or short somewhere....

 

Calling for more grey cells please....

post-11469-0-63345900-1516285420_thumb.jpeg

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NO. All it means is that something is left switched on, & the bulb is simply completing the circuit.

Make sure everything is off, including any radios etc you may have.

 

Bob.

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The ignition problem sounds like it could be a broken lead making intermittent contact. Are you sure the connection from the dizzy to the coil is intact and not broken inside the insulation? Same for the battery feed to the coil + ? Less likely, but if you are using points, is the small flexible wire inside the dizzy making contact?

 

The odd symptoms you quote may just be pure coincidence in the case of the fan if that only happened once.

Your findings with the wiper motor depends on what you were measuring the voltage with as there will be a voltage present on those wires, coming through the motor winding from the green supply lead, so that is not a fault.

 

 

As a matter of interest is your test lamp a normal bulb type or is that an LED ?

Edited by RobH
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The ignition problem sounds like it could be a broken lead making intermittent contact. Are you sure the connection from the dizzy to the coil is intact and not broken inside the insulation? Same for the battery feed to the coil + ? Less likely, but if you are using points, is the small flexible wire inside the dizzy making contact?

 

I thought about that so 1/ shortened the ends of the coil lead and made sure that the contact was frank on both ends - no change and 2/ I ran a live feed from the (+) battery directly to the (+) coil - no change. Last time, i checked the ground wire inside the dizzy and replaced the condenser

 

The odd symptoms you quote may just be pure coincidence in the case of the fan if that only happened once.

 

It happened more than once.

 

Your findings with the wiper motor depends on what you were measuring the voltage with as there will be a voltage present on those wires, coming through the motor winding from the green supply lead, so that is not a fault.

 

OK, that's a relief...

 

As a matter of interest is your test lamp a normal bulb type or is that an LED ?

 

Normal bulb

Edited by Geko
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OK Stef - understood. Obviously the cooling fan is an addition and its difficult to understand how that occurrence could happen, but it might be relevant - do you have any details on how the fan is wired up? Where did you have the earthy end of the test lamp connected when it happened ?

 

Can we assume these symptoms happened suddenly on their own and are not related to any electrical work you may have done recently ?

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With your lamp connected across the Disconnect:

If it lights up when the ignition is off then something connected to the battery either directly or through a fuse is still operating.

If it only lights when the ignition is on, this could be normal.

 

In the first case it is a matter of disconnecting things until the light goes out, and the fan is a prime suspect.

 

Good luck

 

TT

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That was the coil. Tested them and both were faulty (took me a while because it's only after few testing attempts that they gave up). How i managed to toast 2 coils including a new China-made is anyone's guess? Installed an extra fusebox for all electrical add-ons (fuel pump, fan and high beam relays) so hopefully no more disruption.

Thanks gents.

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If they were low resistance coils (circa 1.5 Ohms) intended for ballasted systems it might explain premature failures but I suppose they were 3 Ohm types?

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