Holes in the 'H' frame

[Les Pettitt]

Hi All

If I look behind my 'H' frame, I see there are three 15mm holes in the aluminium former in a line below the radio aperture. The centre hole houses the interior light switch but the other two holes are blanked off by the foam and vinyl covering. Were these other holes ever used or intended for anything else. It seems to me to be a very neat place to put a battery cut off switch. Has anyone else put a cut off switch in this position and, if so, were any problems encountered.

Regards

Les

[jean]

I have put some gadgets in the H frame under the radio, like fan override switch and 12v connector

[trfella]

I've seen photos with two push/pull switches there (either side) to operate front fog lights on original press cars.

[johnny250]

Hi All

If I look behind my 'H' frame, I see there are three 15mm holes in the aluminium former in a line below the radio aperture. The centre hole houses the interior light switch but the other two holes are blanked off by the foam and vinyl covering. Were these other holes ever used or intended for anything else. It seems to me to be a very neat place to put a battery cut off switch. Has anyone else put a cut off switch in this position and, if so, were any problems encountered.

Regards

Les

Hi Les,

i think a battery isolator switch is an excellent idea, just make sure you use heavy cables with soldered or crimped eylets and routed away from anything sharp. I fitted mine to the rheostat postion in the dash and use it all the time, whenever the car is left. I believe you can switch the negative (ground) lead but i didn't...... just remember to stop the engine befor using it.....you can of course fit what you like to the 'H' frame...... MIG29 clock and oil temp/voltmeter for example.......

 

john

[ianc]

Yes, indeed, you can put the isolator in the connection to chassis/ground, which is the negative line on the TR5/6. On my TR4, which was converted to negative earth when it was re-built 16 years ago, that's where the isolator went and, because I have so many extra switches already, it hangs down on a bracket below the dashboard on the passenger side.

As John said, stop the engine BEFORE isolating the battery - if you don't, the alternator loses its reference voltage (the battery itself) and can wind up to its maximum output voltage - I've no idea how high that might be, but it is likely to damage every item of electrical kit which is connected at that moment, including the alternator itself!

Ian Cornish

[razor sharp]

i found the holes very handy when fitting a 12 volt socket....(ie cigarette lighter)

very handy for pluging in satnav etc etc....

[Les Pettitt]

Thanks everyone for the ideas and advice. Ian and John, you have answered the next question I was going to pose. I.e can you use the battery isolator on the negative side? I couldn't see why not but you usually hear of people breaking the positive cable to the starter motor. It always seemed to me much easier to break the earth cable so that's what I'll do. I take the point to make sure the engine is turned off before operating the switch.

PS Just been out today for the first drive this year. Absolutely brilliant. I still get the same kick as I did 30 years ago. How could anyone drive a TR6 and fail to smile all the time.

Thanks again

Les

[Guest ntc]

Thanks everyone for the ideas and advice. Ian and John, you have answered the next question I was going to pose. I.e can you use the battery isolator on the negative side? I couldn't see why not but you usually hear of people breaking the positive cable to the starter motor. It always seemed to me much easier to break the earth cable so that's what I'll do. I take the point to make sure the engine is turned off before operating the switch.

PS Just been out today for the first drive this year. Absolutely brilliant. I still get the same kick as I did 30 years ago. How could anyone drive a TR6 and fail to smile all the time.

Thanks again

Les

 

Hi Les

I was also out today in the five and the six not at the same time and great is was to, and I saw another out as well nice to see the mandatory wave.In my days of motor sport the the isolator switch had to be positive ?

 

Regards

Neil

Edited February 21, 2009 by ntc

[jean]

I would suggest to fit the DURITE battery isolator switch as used in Motor Sport. I have it on my 6 to protect the ECU of the EFI system. It not only isolates the battery power feed, but it is also designed to interrupt the ignition whilst it connects the electrical systems via a resistor to earth and is in so far suppressing what is called alternator surge. I think that's what Ianc is talking about

Edited February 21, 2009 by jean

[TRTerry]

Ian and John, you have answered the next question I was going to pose. I.e can you use the battery isolator on the negative side? I couldn't see why not but you usually hear of people breaking the positive cable to the starter motor. It always seemed to me much easier to break the earth cable so that's what I'll do.

 

 

I might be talking out of my ar*e, but you may find that there are multiple earth paths. The earth cable is there to provide an efficient and consistent earth path for the brutally high currents invoked when starting. If there are other earth paths then all kinds of muck and bullets may happen on starting without the isolator in place as the high currents find the alternative earths to travel along.

[Guest ntc]

Ian and John, you have answered the next question I was going to pose. I.e can you use the battery isolator on the negative side? I couldn't see why not but you usually hear of people breaking the positive cable to the starter motor. It always seemed to me much easier to break the earth cable so that's what I'll do.

 

 

I might be talking out of my ar*e, but you may find that there are multiple earth paths. The earth cable is there to provide an efficient and consistent earth path for the brutally high currents invoked when starting. If there are other earth paths then all kinds of muck and bullets may happen on starting without the isolator in place as the high currents find the alternative earths to travel along.

 

I recommend you don't it should be positive imho

 

Neil

[tthomson]

Hi Les,

 

The holes below the radio aperture in the H frame are a hangover from the TR4A which uses all three for heater control, heater fan and something else (I forget what at the moment).

 

I am fairly certain the H frame is the same assembly in 4A, 5 and 6.

 

TT

 

Hi All

If I look behind my 'H' frame, I see there are three 15mm holes in the aluminium former in a line below the radio aperture. The centre hole houses the interior light switch but the other two holes are blanked off by the foam and vinyl covering. Were these other holes ever used or intended for anything else. It seems to me to be a very neat place to put a battery cut off switch. Has anyone else put a cut off switch in this position and, if so, were any problems encountered.

Regards

Les

[BrianC]

The holes below the radio aperture in the H frame are a hangover from the TR4A which uses all three for heater control, heater fan and something else (I forget what at the moment).

Third one is for air distribution to screen or interior or both (in theory )

[tthomson]

Third one is for air distribution to screen or interior or both (in theory )

 

Hi Brian,

 

Thanks. You are right about 'in theory'!

 

TT

[andy smith]

Third one is for air distribution to screen or interior or both (in theory )

 

Isn't that the last fitting on the left hand side of the panel above the H-frame ?

[tthomson]

Hi Andy,

 

On a 4A the left hand panel switch is normally the rheostat for the panel lamps

On a 4 it is the lighting switch

But I do not know for a 5 or 6.

 

TT

 

Isn't that the last fitting on the left hand side of the panel above the H-frame ?

[Les Pettitt]

Hi Terry,

I'm afraid I'm a bit baffled re your comment on multiple earth paths. My thought was to break the earth lead from the battery with the cut off switch. Once that is broken I can't see there is any other earth path.

For many years I have pulled the earth lead off the battery terminal when parking the car for a few days. This is a throwback to the many years I spent with a slight constant discharge that I eventually traced to the field coils on the alternator. I have now got a new alternator but my son's bedroom is just above the car and I just feel safer by disconnecting a battery lead. I only want to use the cut off switch when parking the vehicle and don't really understand why it would make any difference if I choose the positive or negative feed from the battery.

I would be very pleased if someone could give me a simple explanation of why it makes a difference.

Many thanks

Les

[Alec Pringle]

Hi Les,

 

we're accustomed to seeing the circuit breaker on the positive side on competition cars. Originally, I suspect, because the battery is usually relocated to the rear to improve weight distribution - and the battery is earthed to the nearest convenient point.

 

The positive is usually carried to underbonnet as a single heavy feed, and then distributed from underbonnet.

 

The recognised locations for the mandatory external circuit breaker are immediately below front or rear screens, points at which the main positive feed can be easily interrupted.

 

Unlike road cars, competition cars also have an independent feed exclusively for the fire extinguishing system if it is electrically operated, fed directly from the battery and bypassing the externally-operable breaker. More easily achieved if the main positive feed goes through the cb, rather than the earth.

 

On a road car, devoid of extinguishing system, I doubt it matters much which you isolate - positive or negative.

 

Cheers,

 

Alec

[david ferry]

Les,

 

I am not certain if this is why the supply lead is broken in competition cars but the following certainly makes sense.

 

There is always the possibility in a 'disaster situation' when the earth lead being broken by use of a cut out switch does absolutely nothing as the battery earth terminal is in direct contact with the car body, or has some other route to the car body. This will be sufficient to complete the circuit. The cut-off switch is superfluous as is the earth lead!

 

In such a scenario you would absolutely need the supply lead to be cut. If the disaster were such that the battery supply terminal shorted direct to the car body, I suspect that the battery would explode or horrible welding things may happen with the car body. In this event a battery cut off switch is useless as the battery will be buggered anyway and disconnecting it will do nothing. The car will have 'disconnected' the battery all by itself!

 

On both of my TRs, the cut off switch is on the supply lead and this should always be the case. Never put the cut off switch in the earth lead.

 

You simply have to do the job properly in terms of insulation etc.

 

Apologies for the terminology used...supply and earth...This is to stop confusion as there are both positive and negative earth TRs, although not TR6s!

 

David

[Kiwifrog]

Just to add fuel to the fire I was of the understanding that a lot of the cars switched electrical items, Horn wipers actually switch the earth return ? Have not got a wiring diagram in front of me but I remember something like that ???

 

Alan

[Alec Pringle]

FIA Appendix J 2009, Article 253-2009 Safety Equipment

 

"

ARTICLE 13 : GENERAL CIRCUIT BREAKER

The general circuit breaker must cut all electrical circuits, battery,

alternator or dynamo, lights, hooters, ignition, electrical controls,

etc.) and must also stop the engine.

For Diesel engines having no electronically controlled injectors, the

circuit breaker must be coupled with a device cutting off the intake

into the engine.

It must be a spark-proof model, and will be accessible from inside

and outside the car.

As for the outside, the triggering system of the circuit breaker will

compulsorily be situated at the lower part of the windscreen

mountings for closed cars. It will be marked by a red spark in a

white-edged blue triangle with a base of at least 12 cm.

This outside triggering system only concerns closed cars.

Application: Compulsory fitting for all cars taking part in speed

events on circuits or hill-climbs. The fitting is recommended for

other events.

"

 

But no mention of whether the circuit breaker should be on the supply or earth side . . . .

 

Cheers,

 

Alec

[tthomson]

Hi Les,

 

In terms of electrical function, it makes no difference at all whether you have a cut out switch in the earth or the supply. If your intention is to disable the car when you have it parked, it can be in either wire.

 

There may be good reasons for connecting the cutout in the supply lead, but the chances of this being important are extremely small and mainly to do with earth straps that are overlooked. If you can see both battery terminals and can isolate both of them easily, then you can go with an earth lead cutout.

 

If you are worried about battery explosions caused by the supply terminal of the battery touching the metalwork of the car, then it is better to remove the earth connection to reduce the possible shorting options, but this is mainly redundant. (In such cases the cutout will not be activated because these drastic problems tend to occur when the car is powered!!)

 

If you intend to disconnect power on impact, use an isolator, but this can be in either supply or earth.

 

In my view all of the "problems" relate to situations where the cutout is not being used.

 

Overall, it matters not a jot - go with what you feel is best for you.

 

TT

 

 

Hi Terry,

I'm afraid I'm a bit baffled re your comment on multiple earth paths. My thought was to break the earth lead from the battery with the cut off switch. Once that is broken I can't see there is any other earth path.

For many years I have pulled the earth lead off the battery terminal when parking the car for a few days. This is a throwback to the many years I spent with a slight constant discharge that I eventually traced to the field coils on the alternator. I have now got a new alternator but my son's bedroom is just above the car and I just feel safer by disconnecting a battery lead. I only want to use the cut off switch when parking the vehicle and don't really understand why it would make any difference if I choose the positive or negative feed from the battery.

I would be very pleased if someone could give me a simple explanation of why it makes a difference.

Many thanks

Les

[Mike C]

I used to think there was not much difference between isolating the earth lead and the supply lead , so I'd isolate the supply lead.Then one day I was "fishing" for a wire behind the firewall with a straightened coathanger.The coathanger wire contacted the battery positive lead and shorted against the bare earthed firewall,burning a coathanger wire imprint into my hand. Now I always isolate the earth-that removes a vast amount of uninsulated metal to potentially short out against as virtually everything on the supply side is already insulated.Given that it was six of one/half a dozen of the other it was enough to tip me into isolating the earth.

[BrianC]

Anyone now planning to fit two cutouts - one on each terminal?

And while we're at it, how about plastic insulated terminal covers as used in most current everyday cars?

And, moreover, should we still be using the original style of exposed-strapped battery?

I hope no H&S freaks are reading this thread.

[jean]

On my TR3 I have inserted the isolator switch in the earth strap, no problems at all under normal circumstances. On the 6 I had to, due to the computer controlled EFI system, put the isolator in the + lead.

Please note that it's not only the battery providing electric power, but also the alternator, and once energized it's living a bit it's own life, so cutting the earth might not always switch off the power output...

Many electric appliances remain under electric tension even if they are switched off