Serious electrical short, TR4a

[qkingston]

I have a almost new Autosparks loom in my 4a, installed during rebuild and worked fine for 3yrs. Recently after a visit to a body shop, I noticed that the main beam flashed on occasionally when turning the steering wheel. I suspected that an earth was occurring in the vicinity of the column lighting switch, possibly contacting the indicator cancelling clip and shorting through the steering column. After some investigation, I managed to move the indicator clip slightly further down the steering shaft; it seemed to be sorted. However, today during final checks before the first show of the season, I noticed the main beam came on again, followed closely by white smoke from under the dash. I quickly isolated the battery and had a good look under the dash and the engine bay. I can see significant melting on the Blue/Brown wire at the starter solenoid terminal, on the Blue/Brown connection to the lighting switch wires and a section of melting on the main loom under the dash (Brown wire) which had melted through the wire insulation and the loom tape.

Obviously I need to find the original cause of the short, but further downstream than that I'm thinking I may need to replace the entire run of the Blue/Brown wire, or even the full loom if other damage might have been done within the body of the loom

Any helpful thoughts on this?

David

[Z320]

Hi David,

sad to hear!

What was the last you did on the car?

Ciao, Marco 

[qkingston]

Hi Marco, the last thing before this fault first appeared was a visit to a Bodyshop, however I can't see why or how that would have affected anything in the wiring under the dash/steering column. The worst of the melting is at the starter solenoid connection, but also I've found melting where the Brown/Blue crossed over an earth wire which has melted through causing a direct short to the body!

David

[ianc]

I'm afraid that TRs in standard form have insufficient fuses - just a couple in the TR2/3/4.

As you are going to have to carry out significant re-wiring, I suggest you get Autosparks to incorporate more fuses.

Back in 1962, the Works' Competition Department employed a Lucas technician to wire the four TR4s. and each car has 4 fuseboxes with 4 fuses in each.

Mine has a few more as I have modified the electrics over the 54 years I have owned the car.

Ian Cornish

[qkingston]

That's interesting Ian, they clearly saw the issue. I added an extra fuse box during the build, but unfortunately the Brown/Blue is un-fused, straight off the battery via the starter solenoid

David

[RobH]

Unfortunately you are right that the loom may have  been compromised David.  If the part of the wire in the open-air has melted, any part of it bundled inside the loom will have been even hotter and may have done damage which will only become apparent with time, even if you do replace the bits you know about. 

Sorry that isn't exactly 'helpful'. 

 

 

[Charlie D]

+1 for what Rob has just said.

I've had this happen on a couple of cars over the years.

However it may not lead to a complete re-wire.

Cut back (unwind) the binding of the loom from where you see the damage and keep following it until you get to the other end. Almost certain that the adjacent wires (not actually carrying any current that caused the problem) will have also melted. But you will eventually find places where no damage has occurred.

You should be able to cut out the damaged wires and  replace (using the correct sized wire.)

It's a fiddly process, involving getting under the dash, but if you fitted the original loom, you will know what I mean.

As for what caused it, I don't know, but at least you should be able to identify what wires were the most burnt and so identify the circuit that they relate to.

Charlie.

[had17462]

Just asking would it be covered on your car  insurance .

Nick

[Z320]

David,

I‘m a bit confused….

The cable from the batterie via the solenoid is black and very solid! Your TR is on fire before this is serious damaged….

The cable from the ignition switch to the solenoid is white-red, isn’t it?

Brown-blue is the cable from the A1 regulator terminal (as good as the battery) to the light switch?

Do you use no LED bulbs and always drive with light switched on?

Ciao, Marco 

[qkingston]

Marco, I have an alternator so the cables are slightly different. The Brown/Blue is from the starter solenoid but a common connection to the battery main feed so effectively direct from the battery

[qkingston]

Charlie, that is my thought process. Interesting that certain parts of the Brown /Blue cable run are showing insulation melting, others are not, I don't fully understand what creates the difference

David 

[Z320]

David,

I’m even more confused…..

You used a standard new loom, which is made for a TR4A with generator.

And you used the brown-blue cable to connect the battery with the solenoid?

It has not the dimensions to do this!

And I don’t know where you can buy the colour combination in the needed dimension to use it for this.

Your photo is from under the dash?

Some more and better photos are needed, please.

Ciao, Marco 

[Charlie D]

Marco,

The Brown/Blue cable will be FROM the solenoid TO the rest of the car. The thick Black cable will be FROM the battery TO the solenoid.

 

[gloide69]

Because the main beam was flashing on, it suggests a problem with the lighting switch rather than a short to earth, as the lights are earthed at the lamps.

I'm guessing the lighting switch on the 4a is on the steering column. During your investigation, could you have trapped the Brown/Blue wire near the lighting switch or on part of the steering column loom?

Paul

[harrytr5]

Please don't mess around get a new wiring loom.

I stripped out a burnt wiring loom and when investigating even further into the wiring loom it was a mess. Do not risk it!

Regards Harry

[michaelfinnis]

 

37 minutes ago, gloide69 said:

Because the main beam was flashing on, it suggests a problem with the lighting switch rather than a short to earth, as the lights are earthed at the lamps.

I'm guessing the lighting switch on the 4a is on the steering column. During your investigation, could you have trapped the Brown/Blue wire near the lighting switch or on part of the steering column loom?

Paul

The headlight power supply passes from the switch to the lamp and then to earth. If the lamp was flashing it can’t be because the lighting cable in the dash area was shorting to earth, but was shorting to a power supply, ie an adjacent live cable.

Mike.

[qkingston]

1 hour ago, gloide69 said:

Because the main beam was flashing on, it suggests a problem with the lighting switch rather than a short to earth, as the lights are earthed at the lamps.

I'm guessing the lighting switch on the 4a is on the steering column. During your investigation, could you have trapped the Brown/Blue wire near the lighting switch or on part of the steering column loom?

Paul

Yes that is possible, thank you

[qkingston]

4 hours ago, Z320 said:

David,

I’m even more confused…..

You used a standard new loom, which is made for a TR4A with generator.

And you used the brown-blue cable to connect the battery with the solenoid?

It has not the dimensions to do this!

And I don’t know where you can buy the colour combination in the needed dimension to use it for this.

Your photo is from under the dash?

Some more and better photos are needed, please.

Ciao, Marco 

Marco, Autosparks provide a new loom which is designed for an alternator and with no Control Box. I'm going to strip back the loom tape as Charlie suggests and look at the condition of the other adjacent wires; then decide how to proceed

David

[qkingston]

Also looking at the 'Flash to Pass' wiring which I know has been covered on this Forum as well as those Stateside. The alternative wiring arrangement which I have used without issue since rebuild is attached, showing the connection of an unfused live to the flash terminal on the column switch. I'm wondering whether the live supply should come from a permanent 12v fused supply so the fuse would blow before any serious cable damage occurred? Any thoughts on the pros/cons of these arrangements

David

[RobH]

Ideally all circuits should be individually fused, as they are on a modern car.  That way you have protection for the smaller wiring and lose only one function in the event of a fault but it does imply a considerable change from the standard arrangement.  

A compromise would be to fuse the major feeds only which should include the lighting circuits - it's a puzzle why Triumph never did that really as it is pretty easy to arrange.  Doing that does imply having to use higher-rated fuses though, so the skinnier wiring downstream isn't quite as well protected. 

[RogerH]

My understanding of TRiumph's  action of not fusing the lights (apart from cost saving) is that installing the wires in a safe

fashion was more reliable than using the fuses of the time.  -  you didn't want the lights going out just at the wrong time.

How often did under-dash fires start in the 'old' days.   It seems daily at present.

 

Roger

[Z320]

20 hours ago, qkingston said:

Hi,

I can't help on thís thread with an induvidial loom,

but what I see on the photo above is a poor crimped connector on a cable that has been glown.

This remindes me to a (from a friend) wrong connected ampere gauge

(connectors without insulation blocks between, voltage directly on the gauge body).

Luckily the ground cable of the gauge illumination was the "fuse"

and the metal to metal conatct to the dash board was poor!

Ciao, Marco

 

[ianc]

To avoid the problem of most or all lights being extinguished in the event of a short-circuit, the Works' TR4s have a fuse for each of the filaments in the headlamps (i.e. 4 fuses) and separate fuse for each of left, right and centre spotlamps and for reversing lamp (single filaments, of course).  Centre was fitted on top of the bonnet for some rallies, and Mike North has copied this on his TR4 (LNK).

Ian Cornish

[stillp]

Fuses are very good at blowing when there's a short-circuit, but don't blow quickly enough to protect against overloads.

Pete

[Dic Doretti]

I routinely put a fuse in the lighting circuit (in the main feed) having experienced shorting in the rear lights which means a long run of wiring is compromised. The original fusing on my TR2 was minimal which cannot be good. Better safe than sorry even if it is not original.

Cheers

Richard