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MG TD TF 1500 - Isolation Switch

I am about to undertake the conversion from positive to negative ground, I know there is a thousand reasons not to, and as many to proceed.

In the process I am thinking of fitting an isolation switch, again there are arguments to fit it into the ground side and as many to fit it into the live side.

I am fully cognizant of the need to remove the ground cable first in any maintenance activity, but in this case I think a bracket affixed to the front side of the battery box above the starter switch would be a good location.

I did see one where the switch was mounted through the front of the toolbox with the terminals outside and the "key" inside. I am loath to give up any toolbox space, but could mount it near the top I guess. I will be fitting new batter cables, thinking of getting custom red cable for the positive side and returning to the "strap" for the negative side, or even getting a short black cable. I found a source for custom cables on Ebay.

Any arguments pro/con are both welcome. (Pictures also)

Thanks.

Peter
P G Gilvarry

Peter, here's what I did.

My car had 3 holes in the toolbox, cowl side, in each upper corner. I'm pretty sure these are on all our cars. I used those holes to mount a piece of plywood on the inside of the car. That gave me a place to mount an isolation switch right next to the steering shaft, through the plywood and completely isolated from ground.

I made cables by using welding cable (#2 Superflex, widely available), lugs from my local auto parts store, and a lug crimper I got off EBay for about $12.

So on the ground side, the cable goes from battery through the bottom of the battery box (I think I just used the hole for the oil pressure pipe) to one lug of the switch. The next went from switch along the firewall down to the bolt that holds the engine ground strap.

So, no new holes, a neat and nearly invisible installation, and maybe most importantly, a reachable isolation switch, just in case smoke starts leaking while you're driving merrily along.
MC Logan

Converted to negative ground some 20 years ago. Glad I did. Saves a lot of confusion. When I installed the cutoff switch, put it inside, out of sight, under the dash, so I can cut it off and on easily. Why would you want it under the bonnet so you have to exit the car and open the bonnet? In case of a short, you would cause major damage during that delay.
Larry Brown

I fitted my switch beside the fuel pump on the battery rail and is connected on the power side so I have no heavy wires going through the toolbox or the bulkhead and no holes to be drilled anywhere. Only a short cable between the starter solenoid and the switch is required. The terminals on the switch are protected by a thick rubber cap. It is operated via a T-bar pull cable mounted next to the steering column. This cable runs out through the same grommet as the oil pressure line to the gauge.
Disadvantage is that I have to lift the bonnet to re-set the switch.
Regards
Declan



D Burns

The T bar is beside the steering wheel and does not look out of place as most people think this is the choke lever.
Regards
Declan


D Burns

Mine is a hidden switch under the dash. The switch body and cables are in the engine compartment above the wiper (its a TF). The shaft of the switch projects through the bulkhead so that it can be turned on and off from the driver side.
Dave H
Dave Hill

I see your thought Larry Maybe I need to investigate a hole in the bottom of battery box and a switch under there. I believe Declan has a cable operated one in the engine compartment that he can pull from the driving position.

I have not seen one of them during my search

One of my thought processes is keeping the wiring length to a minimum, I see MC is using 2G which negates that issue.

Looks like Declan was answering while I was typing. Where did you get that switch Declan?

Peter

P G Gilvarry

This was my solution, on the ground side. Inexpensive and easily 100 percent reversable.
Be well,
David


D. Sander

And this:


D. Sander

Another shot


D. Sander

Peter,
They are used in camper vans, boats, racing cars and by the military. They come in various ampere ratings.
https://www.google.co.uk/search?q=Battery+main+switch&biw=1920&bih=888&tbm=isch&imgil=r8Ouw9bLrBd63M%253A%253BjHfHp2OcJz8OcM%253Bhttp%25253A%25252F%25252Fwww.mecmarine.co.uk%25252Fshop%25252Fvetus-battery-main-switch-75amp%25252F&source=iu&pf=m&fir=r8Ouw9bLrBd63M%253A%252CjHfHp2OcJz8OcM%252C_&usg=__SxUXTkhv0mwDA5Xm3BL5dLwBEJk%3D&ved=0ahUKEwjR4KLTp67SAhXI1xQKHUAnD0sQyjcIJw&ei=YBOzWNGwFMivU8DOvNgE#imgrc=r8Ouw9bLrBd63M:
Regards
Declan
D Burns

I'm rewiring my TD as we speak. I'm moving mine from the top of the battery to a spot under the dash. The main reason is, when it was inside the hood I had to open the hood to get at it. In a more convenient place, I'm more likely to use it.

And.... (When I forget) I HATE getting back out of the car to flip the switch.
MAndrus

D. Sander, did you make a long bracket mounted to side of battery box as both the support and the ground connection.

I see where you hide your spare keys, I was going to hide mine in the tool box.

Thanks.

Peter
P G Gilvarry

I am relaxed about originality and have fitted a modern, compact battery which has given me more room to fit a master switch. I also have an alternator conversion and the picture shows some hidden extra fuses.

Jan T


J Targosz

Declan, looking at your switch you have the cable "rotate" the red handle to the off position?

That makes sense to me.

Thanks.

Peter
P G Gilvarry

I AGREE WITH LARRY 100%,, Put it where it can be shut off in a hurry!! Just imagine that you are motoring down the road and you detect something is wrong electrically. Its going to take valuable time to bring the car to a safe stop, get out, open the bonnet and switch everything off. During that time, you could possibly start a fire. Just like a race car, you want the switch to be easily and quickly accessible. I mounted ours on the scuttle hoop, just above the trannie. If there is an electrical problem it's right there to be used. As an added benefit, it is now "second nature" to turn it off when ever we stop. No need to worry about a short if we are not there to do anything about it.
FWIW, I had one of those green cut off switches that you mount on the battery post fail. From normal use, turning it on and off it got very pitted, and wouldn't allow the battery to charge.
Steve
SPW Wincze

I used battery cables and located the switch on the hot side. Ours is still positive ground.
Steve
SPW Wincze

There are a lot of ways to do this. I put a switch on a hidden bracket clamped under the dash. Leads in from the battery through a grommet in the firewall. It's on the ground/earth side (still +ve on my TD). Very handy to shut off... so I always do when parking, as some security. Switch on the ground side makes sense to me as it meant less wiring (I could find a good ground near the switch) so could do it with one existing hole in the firewall. It also means that any short on the switch wire will do no more than making the car operable, as before the installation. Works fine.
I'd say a battery shut off switch is an important step to safety fast, on the road and in the shop too.
Cheers, Peter
Peter Pope

Peter,
Yes, an "L" shaped piece of flat stock, bent at 90' with a 5/16" hole drilled in a hole end. I brazed a 5/16" BSF nut on one end. Fully revrsable with a 5/16 BSF wrench in just a few minutes.
Be well,
David
D. Sander

Peter,
Yes the cable rotates the red key to the off position. It works great and no drilling involved except to mount the switch on the battery retainer bracket.
Regards
Declan
D Burns

Thanks folks for all the input, consensus seems to be:

1. operable from inside the cockpit

2. in the ground side as that is the safest route. (Short to ground only makes the vehicle operable)

I am thinking of removing the left seat (RHD) for a few days to look at/tidy up dash wiring etc. That might be a good time to look for a spot within reach of my driving position.

Maybe a large flag attached will make it easy to spot.

Again thanks for the input, I do like Declan's setup, reminds me of my emergency handles in the aircraft I was on.

Thanks.

Peter
P G Gilvarry

Would it be possible to see some photos of the switch mounted under the dash (interior switch) and how/where the cables go through the firewall?
thanks,
Tyler
C.T. Irwin

This thread was discussed between 26/02/2017 and 27/02/2017

MG TD TF 1500 index

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