TR6 Help! melted wire in my TR6

[ichthos]

I hooked up my courtesy light wire to the switch on the right side. (I stll can not find the driver side courtesy light wire - as I mentioned in a previous post, the PO may have cut the wire somewhere in the harness and rewrapped it). The courtesy light is currently not hooked up. Last night as I was driving, smoke started coming from under the dash. The wire melted from the passenger side switch all the way to the driver side plug. A white wire connected to it also melted. What would cause this? I am also wondering what amp fuses should be in the fuse box. They are not burning out when I have electrical problems. This is the only thing electricall not working in my car a the moment. Any help is greatly appreciated.
Kevin

 

[TR3driver]

That junction with the white wire seems highly suspect IMO. Normally, white means (ignition) switched but unfused. But the courtesy lights should be powered from the purple circuit (which is unswitched, but fused).

Although the books say the fuses should be 35 amps, that is in an obsolete British fuse rating system! The system used to rate American fuses results in a value that is roughly half. So, you should either buy reproduction Lucas 35 amp fuses from the usual suspects, or use AGC 20 fuses. Using AGC 35 is a definite no-no!

But even with the correct fuses, it is possible to have a short that will melt the wire without blowing the fuse. For an added measure of safety, you could break up the purple circuit into 3 separate circuits, each with it's own fuse. Eg, one fuse for the horns, one for the "flash to pass" feature (each of which could be around 10-15 amps), and one for all the courtesy lights (which could be around 10 amps).

 

[DougF]

Old wire with cracks or cuts are very susceptible to shorts.

 

[SpannerMan]

I am looking at the 70-71 diagram, which is what I have anyway and I don't imagine this part of it changed much. The only PW are on the ground side of the courtesy lights on the tunnel and the trunk, and the only PW that should be at that place up under the dash on the driver's side would be for the tunnel lamp. I think the PW wire at the bottom of your photo is coming back from the ground side of the tunnel lamp, and should be connected to ground, completing the circuit, by either of the door switches. The white wire coming from the top of the picture, as Randall said, seems wrong, since if it is coming from the top through the bulkhead it is probably connected directly to +12V. If it is a switched +12V then you would have a direct short to ground through the PW and your passenger side door switch when that wire is powered, which seems to fit with your report. (The bottom PW is not melted because that is leading to the courtesy lamp which is at 12V.)
I suggest to start by disconnecting both wires from the bottom PW wire. You can try *momentarily* jumping the bottom PW wire to ground (the dash metal) and seeing if the courtesy lamp lights. If so you then need to set up the same condition when the doors open by connecting this to both of the courtesy switches. (I would expect to see the PW wire for the drivers door switch in place of the white wire.) That melted passenger side wire will probably need to be bypassed or you might get away with it, hopefully the worst that would happen would be it finds ground and lights the courtesy light. The question would be whether it melted the insulation on any of the wires next to it in the harness which could cause other issues, and in reality cause problems, potentially serious, regardless of what you do with the known melted wire from this point forward. It would be down to your comfort level in hoping for the best. Others may have more experience with that- I've never cooked anything that badly! Good luck, hopefully a starting point at least. Pete

 

[DNK]

Randall I wonder if that "W" wire is from the car or just something the PO just added it.
Kevin you need to find out where that wire goes.
I know you are still looking for the wire in the harness for the door switch. Is there a wire on that switch now?

 

[TR3driver]

Randall I wonder if that "W" wire is from the car or just something the PO just added it.
Kevin you need to find out where that wire goes.

Exactly the point I was trying to make, Don. The white wire doesn't look original, but needs to be checked out.

Just as a cautionary tale, when I first started poking around under the dash of my Stag, I found a heavy black wire that was cut and left dangling. Looked like it should go to ground, but I didn't find a mating ground terminal, so I left it alone. Later, when I had the dash out, I discovered that the other end was twisted into a brown wire ... if I had grounded it, I would have had a direct short with no fuse!

 

[smaceng]

Kevin, you said that you hooked up the courtesy switch to the light wire. Just because it may be the right color, doesn't mean that the PO didn't reconnect it to something else. In electrical wiring, never assume anything. Always check each wire out with a meter to ensure that it is what it is supposed to be. My guess is that the wire you hooked up had power hooked to it, and then hooking to the switch grouned it somehow throught the switch. Also, with a car like yours were additional wires have been added, trace down all these extra wires and add them to your wiring diagram.
good luck,
Scott in CA.

 

[DNK]

Anybody hear from Kevin today, he didn't burn his car up did he???

 

[smaceng]

Probably busy working on the Bugeye!

 

[DrEntropy]

M'gawd, Don!! Don't even ~think~ stuff like that!

*sheesh*

 

[ichthos]

Sorry it has taken me so long to reply. I do not have internet access on the weekends now. Thanks for all the info, but I am not sure I totally understand. I didn't get the chance to test the white wire, but I am pretty sure it is hot now. Why would the wire only get hot when I closed the door?

I should probably just concentrate on hooking thigs correctly at this point. Just a few more questions. 1) Can someone describe to me how the wiring is supposed to be hooked up, which would include the courtesy light and swtiches from each door? Is it just a matter of hooking a p/w wire from each door switch to the p/w coming from the tunnel (courtesy) light? 2)Anyone know of a source for p/w wire (I am not sure what gauge it is)? I probably need around 8ft. I am trying to keep stock colors for the wiring.
Kevin

 

[Deleted member 8987]

You mean the white wire has power, but only when you close the door? Nah. If the white wire is power (as in, unfused ignition), and the PW is a ground for the switch (don't remember, but most door switches are one wire that ground through the switch to the body) you shorted to ground. Usualy power is to one side of the lights, the othert side ground through door switches and/or dash switches.

 

[tr6_easyrider]

I have a '71 Tr6 with that white wire hanging down and it is a switched wire.
Could never find what it was for so I used it for a temp. power outlet for my phone charger. Hope you didn't damage your switch.

 

[TR3driver]

You said this was a 69, right? Then yes, the PW from each door switch gets connected to the PW that comes from the tunnel. Some of the later years were a bit more creative.

As TOC said, the PW wire is grounded only when the door is open. If you put a voltmeter on it, it should be at 12v with the door closed. The white wire (if it is connected as the original white wires were) would be hot only when the ignition switch is on.

AFAIK, the only sources for PW wire would be one of the vendors like British Wiring, or maybe stripping an old original harness. It's very difficult to buy aftermarket wire with color stripes, unless you buy 1000' at a time.

The original PW wire was probably 28 strand (approx 14 AWG); but since the current is always limited by the bulb(s), 18 AWG would do.

 

[smaceng]

Kevin, Attached is the part of the wiring diagram for a 1969 TR6, from what I have checked out the 70 and 71 are different.
In general, all doors, glove box and trunk lights work the same way. A purple wire, which is fused, is connected to a light. The opposite side of the light (purple/white) is connected to a switch. The switch should work that when the plunger is out(i.e. door is open) a connection is made to the chassis or ground (the brits call it earth, but I'm 'merican) through the purple/white wire. Since a connection is made, current flows from the battery, through the fuse, through the lamp, through the switch and into the body to return to the battery, and the light goes on. When the plunger is pushed in, the purple/white wire is no longer supposed to be grounded, but is open. Since current can not flow, the light does not turn on.
Since a TR6 has two doors, it has two switches to turn on the lamp. They are wired in parallel, so that either open door can turn on the lamp. I notice that the transmission lamp also has a switch to turn it on.
Now: Why did the white wire heat up when you shut the door?
I don't know, but most likely battery voltage went to ground, which draws a lot of current and the wire insulation melts.

You need to make sure the wiring is just like that shown in the drawing, and that purple/white wires are not connected to battery voltage. Also check that the switches operate as discussed above. Good luck
Scott in CA

 

[ichthos]

I don't have much time on the internet, but thanks to all of you for your help. I went back to check things out after all the advice and found out that
the white wire is in fact a switched wire that goes directly to my fuse box as a number of you stated. It makes sense to me now that it was when I turned the switch the heating of the wire started. Do you think the white wire was originally designed to power the cigarette lighter? I can cut open the wiring harness and replace the white wire easily. It shouldn't be a problem to run a wire from each door switch and connect it to the p/w wire either. I do have a new problem now. Took my wife out for a quick bite to eat and found out that the rear lights and running lights do not work, and occasionally the headlights, and brake lights stop working. I am guessing that I have a short(s) now in some of the wires which I will probably find when I cut open the harness?
Kevin

 

[DrEntropy]

You should open up the harness and physically check the wires. One getting hot enough to melt insulation will damage others in the bundle too.

 

[TR3driver]

That said, I got by for many years on my TR3A by just cutting off the melted wires and running new replacements. But I checked all the other wires for shorts first.

When the Stag suffered a meltdown (brown wire shorted to ground inside the steering column), I pulled the harness apart and found only one place where another wire was damaged badly enough to require replacement. And since it was only shorted to the melted wire, it would have been OK to leave it as above.

 

[ichthos]

Randall, that is what I am hoping for - a few wire repairs at best. Like you said, I can just add a wire, but I have to make sure that where it melted that is did not ruin other wires. I probably won't get a chance to get at the wires until the weekend.
Kevin

 

[TR3driver]

Er, I probably wasn't clear. On the TR3A, I just used an ohmmeter to check for shorts, rather than pulling apart the harness. I had actually planned to replace the harness eventually, but since it never caused any more problems ...