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Front fog lights stay on after flashing


eebee

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Posted (edited)

Chasing my tail on this one.  Car is 1974 Targa.

Front and rear fog lights operate as they should unless I flash OR turn on to main beam, whereupon the front fogs stay on as lights return to dipped beam, unless I pull (turn on) and then push (turn off) the fog lights switch. 

I have traced the problem to a residual 5v which stays at pin 85 of the fog lights relay.  

If I break the yellow wire from the ignition switch (at the inline connector under the dash) the dipped beam doesn't work, but the fog lights now operate as normal, and the 5V at pin 85 of the relay disappears. 

I'm wondering if pin 85 should be grounded, but I don't want to break something.  It has a white wire connected from relay 85 to fuse 8.  Top of fuse panel, with Blu and Blu/Wh connected to the bottom of the fuse.

I believe everything operated fine (but am not certain) until I recently fit the headlamp relay kit.  If I pull the dipped beam cube relay, this also fixes the problem, but of course, I lose dipped beam.

 

My fog lights switch is a pull (for fronts) and turn (for rear).  Wires(pin out) connections are:  Gnd - (Bn); NR (Wh/Grn); N (Blu/Wh); 58 (Grey (or perhaps dirty white))

Got me stumped.  Would appreciate some help.  

 

Edited by eebee
correction of text
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Are your foglights factory fit?

Have you tried fitting a new relay to eliminate that?

Maybe you need to remove the headlight relay back to standard to see if that fixes the issue. Then you will know if the problem lies there.

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Posted (edited)

The fogs are wired so that they turn off with the main beam.   Your coil 85 white wire is effectively grounded through the headlamp bulb when the mains beams are off.  When the main beams are on, the potential is raised to 12V turning the fog relay coil off (because both sides of the coil are at 12V).

If you’ve installed relays on the ‘bottom side’ of the fuses, you’ve lost the ground path through the bulb filament so you would have to move the white wire to put it on the ‘top side’ of the bulb.

Of course, what you should have done is get one of my fuse panels then this would all have been taken care of.  :)

 

 

 

Edited by Jonny Hart
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On 31/05/2021 at 09:34, Jonny Hart said:

The fogs are wired so that they turn off with the main beam.   Your coil 85 white wire is effectively grounded through the headlamp bulb when the mains beams are off.  When the main beams are on, the potential is raised to 12V turning the fog relay coil off (because both sides of the coil are at 12V).

If you’ve installed relays on the ‘bottom side’ of the fuses, you’ve lost the ground path through the bulb filament so you would have to move the white wire to put it on the ‘top side’ of the bulb.

Of course, what you should have done is get one of my fuse panels then this would all have been taken care of.  :)

 

 

 

Thanks for the reply Jonny.  I'm not understanding your meaning of 'bottom'? I followed the headlight relay instructions and wired the control wires in line with the original wires going to the top of the fuse panel (for main and dip).  Is this incorrect?

I'm really not sure where the white wire from really 85 is supposed to go on the due panel, as the fuse panel wires were all over the place, with lots disconnected when I purchased the car as a restoration project. It's currently connected to the top of fuse 8 (counted from the RHS side) There were also alarm wires everywhere.  The wiring might not be correct.  I've followed as many diagrams and pictures as possible to get it all working.  Here's a photo...

 

BTW.. I have thought about your fuse panel upgrade.. plans for later this year.

IMG_4266.thumb.jpeg.7d7c5eed635fc71572adace6c18b87c9.jpeg

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Posted (edited)

@Jonny Hart Had a thought... do you mean the white wire on pin 85 of the fog-light relay should splice into the white wire going IN to the new headlight relay?  Currently it is connected to the Blue OUTput wire from the new relay - connected at fuse 8 (counted from the front of the car) of the fuse panel (see photo)

 

BTW, I realise 5&6 and 7&8 are joined on the back of the fuse panel.  I originally copied what was there in case on changes by the previous owner.  Though on check with a meter, 7&8 are definitely joined at the top of the fuses.

 

Edited by eebee
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Posted (edited)

Finally I have some time to get back out to the garage today - will get the meter out and have a look again at the voltage levels.   

Keep those ideas coming fellow IB'ers.  🙂

Edited by eebee
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ALL FIXED!

Spliced the wire wire (to in 85 of foglight relay) to the white Input wire of the headlight relay.  It was wired to the the Blue output wire of the headlight relay. Fogs now working perfectly, as per the owners manual.

Thanks for the tip @Jonny Hart

 

Pictures below.  I did redo / tidy up by feeding the wires behind the fuse panel.

IMG_4280.jpeg

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