• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Lighting circuit - the smoke's escaped from the wires.!

Share this page

DerekJ

DerekJ

Luke Skywalker
Country flag
Offline
I am progressing nicely with the re-assembly following the respray. Today I installed the front headlights and sidelights, the rears were already in place. I was pretty sure one of the headlight bulbs was gone so wasn't expecting it to work. Switched on the lights and the right hand head light and sidelight worked as did the right rear. None of the left side worked at all. While I was thinking about the problem smoke suddenly came from under the dashboard and then the bonnet, I quickly hit the master cut out switch I have on the dash. With the lights off the fuel pump was working fine, I didn't try to start the car as I was in the garage.

One thing I had not done was to connect the wires to the rear number plate light as I need to drill new holes to install it. The ends of the wires were taped. Looking at the wiring diagram I believe that not having the number plate light connected would account for the left rear and left front side lights not working. The left headlight has what I think is a bad bulb which is one possible reason why it didn't work. The indicators didn't work on either side.

Question - Could the fact that the number plate light is not connected cause the burn out? I wouldn't have thought so. I checked the light switch connections under the dash and one of the red wires is melted over a couple of inches before it goes into the harness. Any suggestions as to what the problem might be? Plus suggestions to try to locate the issue while avoiding burning the wires when I test them. Is there a short somewhere? Is the red wire likely to be burnt inside the harness?
 
Derek,

You probably have a short somewhere. My first guess would be to check the tape on the ends of the license plate wires. Maybe it came off or isn't fully taped. I don't see how not connecting the light would cause a short, either. Sounds like you got lucky with the red wire under the dash and I doubt the wire is burnt inside the harness. I'd just replace the couple of inches that are burnt.
 
Had a similar issue when I rewired my BJ8; a brown wire--it was for a cigar lighter, which my car doesn't have (do any Healeys?)--apparently contacted metal and the wire melted. I've driven over 100K miles with this harness with no further problems, though.

Sorry, but the wire is probably melted along its length; there is no reason the harness would prevent it from melting inside. I've always considered the entire harness to be a 'fusible link.'
 
Was this an all new wiring harness? I really hate it when the smoke tries to escape like that! Not sure where the problem is, but you might want to start by checking all the light sockets that don't work and the wiring leading to them. You likely should check that red wire more thoroughly for damage. Let's hope that the heat didn't damage other wires that it touched. Using a low amperage battery or a trickle charger as a power source might work better for testing the circuits.
 
Melted wire insulation indicates it was taking more amps than it was designed for, so besides a short check to be sure everything is hooked up where it is intended to be. If the taped up wires include grounds, then the circuit will try to find the easiest path to ground which could have been through that wire.
 
Just been giving the wiring diagram more study. For the first time I've noticed there is a device labelled 'lighting switch' and separate from that another part labelled 'panel lamps switch'. In reality are these combined into the two stage pull out light switch on the dash?
 
Question - Could the fact that the number plate light is not connected cause the burn out?



NOPE Your thinking was good.
 
Derek, the "panel lamp switch" is a small slide switch that is used in all but the BJ8. It is only supplied power with the light switch on and feeds the gauge illumination bulbs. The switch allows you to turn those lights out. You should find it mounted on the lower edge of dash panel. On the 100 it is to the right of steering column. Not sure about the 6 cylinder cars.
I have just spent some time reworking mine as my dash lights would not work.
 
Update. As Bob correctly predicted the wire is burn't out along its length. I have traced it to the front left side light. I believe that is where the short occurred. One possibility is that there was too much bunching of the wires inside the rubber protector boot. Another is a fault on the housing itself. I will buy a new fitting tomorrow and run a wire directly from the switch to the light and see what happens.
 
Hi Derek
Probably the red wire is burned, the problem is if in the harness it has shorted one or more others wires- ​(I hope that damage is limited)
your intention to by pass the red wire to tail lights and instruments light is good-
take care that all the oldest connection of the OLD red wire are disconnected and insulated-
Take also care at the REAR PLATE connections where in the past USA exported car was subject of harness burning due to NOT EXPERT WORKERS connecting the red wire to GROUND
when the rear bumper was refited, after the sea transport
One good remedy to avoid the burn the harness is -
NOT use the battery as 12 V source - a little 12V battery charger (8-10A) with a AUTOMATIC and ripristinabile FUSE protection, will be the better option -
when a short occur the AUTOMATIC Kick off -

Derek you have a Private Message from me
 
Bob_Spidell said:
Had a similar issue when I rewired my BJ8; a brown wire--it was for a cigar lighter, which my car doesn't have (do any Healeys?)--apparently contacted metal and the wire melted. I've driven over 100K miles with this harness with no further problems, though.

Sorry, but the wire is probably melted along its length; there is no reason the harness would prevent it from melting inside. I've always considered the entire harness to be a 'fusible link.'
Click to expand...
imagejpeg
Yes, my 1960 BN7 has a cigar/cigarette lighter on the bottom of the heater box.
 
Last edited:
Back
Top