Twin Cam Special headlights

[rjbaren]

I am mostly polishing the car but I have taken a few spins so far and of course, a question comes up.  The shop I had the car in said the electrical systems all seem to work.  I was out driving near dusk and I turned on the headlights and dash lights and after a couple of minutes driving I smelled what I thought was going to be an electrical fire.  I immediately turned off the headlights and dash lights and made for home.  Everything was OK but I have yet to turn the lights on again.  I have driven the car again in the daylight and all is still well.

I am just being chicken?  Could it be years of dust burning behind the dash?   What would be a safe way to check this out if I do have an electrical problem without burning up the car?  I do have a fire extinguisher but I hope it doesn't come to that.

[GavinT]

If you've already smelled it, I suspect some wiring damage has occurred.
Burning electrics has a distinctive smell.

If it were me, I'd disconnect the battery and check the wiring loom.
Start tracing the Blue wires back from the lights to under the dash. Melted/fused/blackened insulation should be visible.

[BDA]

A wiring diagram (they are available from the main page of this forum) can help you trace which wires you need to concentrate on (interior lights, head lights, turn signal and markers). Unfortunately, the diagram will not necessarily tell you where in the car the wire is but it does tell you what it's connected to and that should be enough to get you started. You should also check your fuses to make sure they are the proper amperage 35A British. You might consider replacing them with actual known 35A British fuses. A 35A British fuse is not the same as an American 35A fuse. You may or may not be able to source them locally but they are readily available from the usual suspects and Brit car places like Moss Motors, etc.

[1970EuropaGuy]

Many of us have added relays for this reason as well. It doesn't cost much and takes the high power load from the switches.

[4129R]

The headlights take their power from the ammeter, it then goes to the fusebox, then to the side light/ main headlight switch, then to the dip/main beam switch, then through two wires (main and dip) to the two headlights.

When the light switch is either in the side light or headlight position, all the red wires for the repeater red/amber lights, rear lights, number plate lights etc are live.

I think from memory they are blue/red and blue/white wires from the dip/main switch to the headlights.

The question is where did the smell come from, behind the dash is the favourite place in my opinion.

To get to those wires behind the dash from the ammeter to the fuse-box, fusebox to light switch, and light switch to dip switch is a bitch. To take out the dashboard is a big job, and you would regret doing it.

Maybe run a fused wire from the battery to the dip switch to narrow down the source. That would by-pass the wiring behind the dash. 

I have replaced 3 wiring looms, so I understand all the routing of all the wires.

[jbcollier]

Check connections along the route laid out by 4129R.  Smell the switches.  You should be able to isolate the problem fairly quickly.  It is a good idea to fit a relay to reduce the load on the headlight switch and hi/lo switch BUT find and fix the problem first!

[rjbaren]

The car hasn't been on the road for nearly 30 years.  The headlights were tested at the shop, one headlight was replaced and I was told everything electrical works.  When I turned the lights on everything worked but, then I smelled something burning.  There was no smoke and I turned the lights off quickly.  When I smelled the burning, it was behind the dash.  I have found no burned wires anywhere yet, but, I have not been behind the dash other than putting a screw in to hold the fuse box in place.
Is there a post on how and where to install the relay for the headlights?  Maybe the headlight switch is ready for a meltdown.

[4129R]

What wattage are the headlights/sealed beam units?

They were 55w, so at 110w in total, they would have been drawing just over 9 amps. Add 6 x 5w for other bulbs, and the total power going through the wiring up to the headlight switch is around 12 amps.

Not exactly wire melting current, unless the wires are corroded at a connection to the lights, to earth, or to more likely the switch. After the dip/main switch, the power splits to left and right front lights, so the 12 amps is going through the main headlight switch, and 9 amps going through the dip/main switch.

[jbcollier]

If the headlight switch's contacts are corroded, then it can heat up for sure.  Just turn the headlights back on and use a piece of hose to "smell" next to the switch.

[4129R]

If the headlight switch's contacts are corroded, then it can heat up for sure.  Just turn the headlights back on and use a piece of hose to "smell" next to the switch.

Preferably polythene, and not rubber, which could disguise the smell.

You could get quite close through the radio rectangular hole.

[BDA]

That's an ingenious way to investigate that but the headlight switch on a TCS is not that far from the edge of the dashboard. I think it would make more sense to take the console cover off and take the switch out. You can inspect the connectors for corrosion or discoloration or other evidence of heat. If they are in good shape and you are still concerned about the switch, you can go further and connect wires between the wires in the loom and the switch so you can get it away from the dash and get a good look at the switch while you operate it.

If you choose to do this, you will have to take the knob off the switch first which means pushing the inset "button" in the knob. Check the manual for details about how to do this.

[4129R]

If you choose to do this, you will have to take the knob off the switch first which means pushing the inset "button" in the knob. Check the manual for details about how to do this.

Those push in knob buttons notoriously rust in place.

I have several broken knobs from various switches and cables where that has happened.

[BDA]

Right! It's best to be careful. If the knob doesn't come off easily, then it might be best to do the hose trick. I do think taking the console cover off is a good idea because you get better access to most things.

Admittedly, my method is somewhat "invasive" and drawn from my experiences (I've had my headlight switch out several times over the years) so it might not be for everyone, especially someone who is not confident in his abilities (or in my case, have an inflated view of my abilities!)

[rjbaren]

Hi, I removed the headlight switch from the dash and let it hang under the dash.  The wires look ok and the contacts look ok too.  I disconnected the negative battery terminal and then put it back on loosely so I could remove it quickly if I had to.  When I turned on the lights and did a quick walkaround all the lights were on, even the license plate lamps in the rear.  I held the switch and wires in my hand for nearly 10 minutes.  The ignition was off but the lights were on but not the panel lights.  At about the 8 minute mark the Brown with blue tracer wire was getting warm.  I decided to turn the lights off and disconnect the battery for good measure.  When I walked by the car again with the windows down I could smell the electrical burning smell from inside the car.  I didn't smell it while I was holding the switch and it is definitely coming from around the dash.

[BDA]

Instrument lights: I assume you turned the rheostat is turned all the way on. The incandescent dash bulbs are not very bright in the first place. You should check that the red wire from the fuse box to the rheostat is good as are the red/white wire from the rheostat to the instrument lights.There is also a red/green wire from the headlamp switch to the fuse for the instrument lights. It's probably either the first or last fuse in the block.

The brown/blue wire comes from the ammeter. Does your ammeter work correctly. What is the condition of the connectors at the back of your ammeter? My ammeter got very corroded and caused all sorts of odd problems. I eventually replaced it with a voltmeter.

I'm assuming that since you had the switch out that the brown/blue wire was the only one that got warm.

The ignition is not required for running the headlights (bad idea in my opinion).