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MG Midget and Sprite Technical - Running wires through the bulkhead???

I need to run two wires through the bulkhead somewhere between the battery and voltage regulator. The wires will be going to a kill switch so they will be carrying the full power of the battery and I am fearful of the insulation wearing through and shorting with all that entails!!!

Is a hole cut, filed smooth and a rubber grommet enough or is there a better way???

I really dont want to burn her to the ground!!!

Thanks in advance....
David Banks

you can get plastic grommets for running 240v cables thru computer cases, or strain relief grommets these will give you more piece of mind as they cannot be chaffed in the same way... however I would be happy with well clipped down wires and rubber grommets
Will Munns

I assume you are taking the positive main cable from the battery to inside the car and connect it to the isolator (kill switch) From there you will then need for it to come back through the bulkhead and back to the starter solenoid. This is very easy using heavy welding cable (multistranded wire) as battery leads. Simply either use eisting holes or drill a couple and use a grommet.

This is how my isolator switch is fitted.
Robert (Bob) Midget Turbo

Why are you putting the kill switch on the passenger/driver side of the bulkhead?
Daniel Thirteen-Twelve

So I can isolate the battery in case any wiring shorts out - how ironic would it be if the wiring I put in to create a safe situation due to a short actually caused the short!!! Hence my cautious aproach!!
David Banks

make it easy on your selfs don't go through the bulkhead with the wires!

in mine there is a batery cut of switch with ignition cut of (no accedental destroing the altentor)
it is fitted through the top of the drivers footwel from inside the engine bay.
the key fits in between the tunnel and the steering column and is easy to reach but can't be seen (anti theft idea)

the wireing is verry easy since the switch is next to the battery and just behind the starter solenoid.
for the ignition cut off just loop the +of the coil throug the apropriate contacts on the switch.

never had a flat batery
and several people tryed to start it ;)
Onno Könemann

I like that idea!!!
David Banks

So long as the cable is well supported (clipped to the body) where it goes into the grommet you won't have a problem as you will need movement to chafe through the insulation.

However, if you are still concerned with fretting through the insulation on the live cable, why not fit the kill switch into the main battery earth? That's how my MGB is set up. Same effect electrically, but if that does happen then there is no short circuit.
Paul Walbran

They make a plastic spiral wiring harness cover that you wrap around the wiring and us zip ties to secure, that would take some time to wear thur and give it a finished look...

remember to use some silicone to seal any holes you drill because the engine heat does try to find its way out of the engine bay anyway it can.

prop

http://cableorganizer.com/wire-loom/split-wire-loom.html?src=sim-prod
Prop

David, You have not understood my question. I did not ask why you are fitting a kill switch. I asked why you are fitting the kill switch inside the driver/passenger compartment.

Daniel Thirteen-Twelve

Paul W's idea of switching the earth is a great one, I guess it would fail the race regs, but for road use it would be almost 100% fail safe.


Switch using hot side failures:

Switch on
short to body, wire heats rapidly, battery may gas hydrogen and boil acid into engine bay - large potential for fire

Switch off
Same symptoms, except only one wire is active


Switch using ground failures:

Switch on
Short to body, no change - car continues running normally

Switch off
All current goes thru short, this means the radio will stay running, attempt to start car with switch off may cause a spark but no overheating (so reasonably safe)


Actually I have rewired my midget using relays in the engine bay to prevent lots of current behind the dash, and I have used the same technique - for me the worst that can happen is the lights stay on!

Will Munns

If you want a switch to stop the engine running (as opposed to isolating the battery) the easiest way is to use a swtich to optionally short the white/black to the rev-counter to earth; in essence, it effectively means the points never open, so no HT. Hard to detect.

Best used with points; not sure of effect on some types of elec ign. Only -ve impact of fretting etc is engine would not run.

A
Anthony Cutler

The reason for fitting this switch is based on a recent problem that the battery was always flat. I eventually tracked it down to a fault in the heater blower switch - at random the blower would come on even though the ignition was switched off - it had been wrongly wired when it was converted to -ve earth. It often came on for a few hours during the night and flattened the battery.

My thought was to completely isolate the battery by putting a switch in the live side. If I had switched the earth side it would not have prevented the problem described above.

[Daniel 1213] I want to locate the switch inside the car for convenience - I don't want to have to lift the bonnet every time I want to use the car.

This way I will know for sure that the battery will not be flat when I come to start her!!

David Banks

Mine is inside the car & on the -ve line, i ran the wires through the existing bulkhead grommet with a layer of heatshrink over the wires for a bit of extra insulation.
Brad (Sprite IV 1380)

David whilst I agree with isolating the positive side and having the switch and cables inside the car, if you had isolated the negative it would also have stopped the drain on the battery. It does not matter which side you isolate the battery will be disconnected from the electrical equipment.

Also I assume Daniel is suggesting having the contacts of the switch in the engine compartment whilst having the switch handle inside the car for operation, that s how I have my MGA wired. My midget however has the whole caboose inside the car behind the centre console and can not be reached easily to short out by a theif. They of course could easily run a jumper wire from the battery to the starter solenoid if they were good at nicking cars.
Robert (Bob) Midget Turbo

Actually David,

There is A HUGE benifit to isolating the battry and lifting the bonnet every time you use the car

I know because I do the same thing, and will absolutly do so in the future!

The benifit....If forces you to spend the extra 90 secounds to look over the fluids and take a fast visual of the engine bay for issues, it may sound like a buzz kill, but I only drive the midget on the weekends, So its easy to say Ill check the oil level in the engine and carbs next weekend, and you know how that story is always told. If the car is a daily driver then its not much of an issue...a running car is a healthy car, a car that is only ran once a week can get sick fairly often if not watched like grandma in a nursing home.

my advise...isolate the battry and gain the benifit of forcing you the check under the hood each time you take it out, its fast and easy, and you get used to it vary quickly....then fix the issue or put a secondaery on/off switch in the blower circuit, that said, I dont kill the battry each night on the weekend. I turn it on friday afternoon then shut it off agian on sunday evening.

With my wiring almost 40 years old... spliced, hacked, and wacked on, it is something to fear on those dark sleepless nights without a battry isolater


Well At least I used to a year ago, and will get to start doing it agian this monday

Prop
Prop

David,

There is a fancy piece of hardware that you can fit through the bulkhead and attach the live wire to each side. It's safer than passing a large live wire through a hole with a grommot but comes at a premium.

I suppose you have already discounted having the switch external on the body?
Daniel Thirteen-Twelve

Thanks guys for all your helpful suggestions. I really don't want anything showing on the outside - I love the clean lines - no bumpers, no door handles etc - I really don't want a bright red knob showing on the outside (I should have phrased that better!!!)

I have installed a key operated breaker like you see on race cars under the bonnet with a cable to the key run into the car - now wires through the bulkhead - guaranteed dead circuit - forces a quick visual check under the bonnet whilst switching it on, can be isolated from driving position if a problem occurs.

Many thanks for all your input.



David Banks

This thread was discussed between 25/09/2009 and 27/09/2009

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