7 replies to this topic

[MiniNev]

Hello all.

So today I decided to resolve 3 things on the car, an ‘85 Mayfair:

1. Interior light not working - turned out to be a blown bulb but cleaned contacts on n/s door as well.
2. Ignition light not working - bulb holder had fallen out.
3. Heater valve cable jammed - dropped the heater matrix took out valve cable, freed up and put all back.

After all that it now appears my lights, hazards, interior light and horn no longer work.

I am getting power to the light switch (brown wire). But there is no power getting to the bottom fuse (last of 4) which I believe power comes to it via a red wire from the light switch.

With the light switch off I can record 12v across fuse 2. When the light switch is on I am seeing no power across the second fuse HOWEVER if I take the top brown wire off of terminal 3 of the second fuse then I do see power across it. With that brown wire off it seems to earth i.e. putting a voltmeter to it and a live feed gives a 12v reading.

Prior to todays ‘fixes’ it was all working fine and I can’t figure out what has happened. Any ideas are indeed most welcome
Many thanks.

[slidehammer]

Is it worth checking you didn't knock and of the wiring connections going to the switches when you dropped the heater and did the cable?

[johnR]

I'd start by checking all your earths.

[weef]

The circuits that are faulty are both associated to two fuses that are fed directly from the starter solenoid, BROWN wires.

Check, relative to a good earth , that there is 12v either side of these fuses. If not check fuse/fuseholder integrity and repair if needed.

The fuse that has the PURPLE/ORANGE wire going from it feeds the interior light circuit and the hazard warning circuit. If there is 12v on the load side of this fuse remove the cover from the interior light and check the 12v is there and note which terminal it is. Remove the bulb from the light and check the continuity of the other terminal  wire to the door switches. If all good the interior light should work, if not the fault will be evident if the 12v or the continuity check shows a fault. Similarly check for 12v at the flasher control unit.

The same fuse/fuseholder checks apply to the other fuse, the 3/4 fuse. It has the BROWN feed and from the same terminal as the supply that feeds the main light switch. Check there is 12v on the brown wire at the switch, then switch to sidelights and the 12v should now be on the RED wire going from the switch to another fuse, 7/8, and then to the sidelights. Again check for 12v either side of this fuse, these checks will direct you to the fault

From the load side of fuse 3/4 there are two PURPLE wires, one feeds the headlight flash and the other the brake light test switch, check these work.

Hope this explanation helps you fault find, and I think the wire colours I quoted correct. 

As an aside you mentioned measuring" across a fuse", my understanding of "across a fuse" is one meter lead either side of the fuse, as opposed to measuring either side of the fuse to earth. If a fuse is good there will be no voltage measured "across a fuse".

[cal844]

There is an online fuse for the purple/orange wire

[mini-mad-mark]

+1 for checking the main feeds from the solenoid - Learn from my bad experience....

 

I had a similar problem but intermittent - spent a good while and stripped out loads of the loom looking for a broken wire or switch issues;  finally found a broken connector at the solenoid that sometimes touched and sometimes didn't

[viz139]

Sometimes with a bad connection you can get a few milliamps through to drive a volt meter but when you switch on a load (lights) it will fail completely and again give a false reading when you remove the load. As above check the brown wires at the solenoid and the main battery cable.

[MiniNev]

Thanks all for the advice and guidance.
So… I have checked the brown feed off the fuse box and cleaned it up again and success I now have lights!
I traced the interior light to the fuse behind the air box (which I had previously taken apart) and wiggling that I got some power so cleaned and swapped the fuse )which was working) and hey presto i now have an interior light again and hazards!
So it appears those two things were just coincidental with the work I had carried out. Plus it just needed more cleaning.
The only issue now is the rear fog light is not working and there is no power to the switch. It looks like this is fed from the headlight switch blue wire via a fuse and comes to the fog switch as blue orange. The big question is where is that fuse as there is only one behind the air box? UPDATE I have found it. There was an aftermarket scotch blocked inline fuse just going nowhere which I presumed was for a long gone accessory. When I looked closer I found a short tail of the required wire so just need to connect back up!
Thanks again all, much appreciated.

Edited by MiniNev, 12 April 2022 - 07:01 PM.