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MG TD TF 1500 - How to Keep Only Clock Connected

I just posted about a shutoff switch to my TF. I found the new one I purchased years ago - the cheap one with the green knob you unscrew at the battery post, and am using it for now.

However, I guess I want my cake and eat it too! I would like to keep the clock connected so I do not have to constantly reset the time.

1. How best to do the wiring so it runs when the battery know is off?

2. I read one note that said the positive is always searching for a ground, so would this put the car in jeopardy and negate the reason for disconnecting the battery in the first place?

I know some of you brains out there will have an answer - maybe even opposite ones!

Keith in NJ

Hi Keith, You can keep you clock running with the remote switch in the off position by installing the fused link adaptor as shown in the image for that purpose. It quite often comes with the purchase of the cut-off switch. I do not understand the comment about the"positive always searching for the ground", rather I agree with D. Braun that as long as either positive or negative battery terminal is disconnected, there is no longer a live circuit, and therefore no chance of a short. Cheers Phil

Phil Atrill

Keith ,
I did much the same as Phil shows ...except I used an "old school" type inline fuse direct from battery + to my clock. My electricial system has several "added" fuses and I wanted to keep them all the same style. (I would have to look ,but think I used a .25amp fuse on it?) My car is negative ground! You + or - ground?
Thanks for asking ...thought I was the only one too lazy to reset my I didn't even mention it before. LOL
Here is my "mod":
David Sheward


First of all, I'll admit that my TD clock is right twice a day.

If you add the inexpensive shut-off switch, you can jump from the battery terminal clamp on the switch to the clamp on the cable with one of the in-line fuse devices shown by Phil or David Sheward.

25 amps, though, is a lot for the clock, and a dead short somewhere else will need to blow that fuse in the event of a problem. For example, 12 volts times 5 amps is 60 watts, which is enough to power a headlamp on mainbeam. Plus, as Dallas said, with the fused connector, anything running on the car from the hot side may find a sneak current regardless of the side that the shut off switch is on, unless the battery is completely eliminated from the wiring harness. The fused link doesn't completely isolate the battery. The only thing that might blow that fuse with the shut-off switch 'open' is the starter, or perhaps the horns. So it kind of defeats the purpose of having the shut-off switch.

I think I would simply reset my clock, but then again, mine doesn't run.

Dave Braun

Dave, I think David was referring to a .25 amp fuse, not a 25 amp fuse. Please correct me if I am wrong. Cheers Phil
Phil Atrill

I knew I could count on some answers!

Phil - it is hard for me to judge perspective, but is the ring on your fuse wire big enough to put over the battery negative post? (mine is the wire braid negative ground) It looks like both ends are the same size - I guess I would just somehow connect the other ind to the clock power feed wire.

I would also think it was .25 not 25 amp - would a 1 amp work or too heave do you think?

David S - What kind of spare spark plug holder is that? Looks nice! I looked at your images - impressive, but hard to see the old school line you are mentioning.


Keith, The terminals on the fused link attach between the battery cable's terminal clamp screw and the cut-off switch battery's clamp screw, hence the ring opening is only about 3/8ths. The clock will draw very little current, so you could probably get by with even less than a 1 amp fuse. Phil
Phil Atrill

1 amp would be a better choice than 0.25 amps. fuses below 1 amp start introducing resistance into the circuit, which in the case of the clock probably isn't be a problem. A more eloquent solution is to use a polySwitch pPTC P/N RGEF500. This is a 5 amp fuse that will reset itself after any short circuit is removed. Cheers - Dave
David DuBois

Think about this for a moment. The battery disconnect is done to prevent current being drawn from the battery. These devices being talked about are various means to get around the disconnect. Any attempt to draw current from the battery will flow through this device. If you forget and turn the key on, the current for the ignition, fuel pump, etc., will try to flow through this device and will blow the fuse, trip the breaker, etc..
IMHO, it's much simpler to just reset the clock. Bud
Bud Krueger (TD10855)


If you are right, that is a good point. No doubt I would try to start the car at some point without connecting the battery. If this is true, I don't think I am going to do it.

Any other agreement or not with this out there?

Ideally, maybe I could get a small 12v battery and have some type of automatic (or manual if needed) switch over when the car battery was disconnected.
I know this is not an electrical BBS, but maybe someone knows if this is viable or how to do it?


Keith, a quick back-of-the-envelope sketch shows that it probably can be done with the use of a common 12v SPDT relay and a 12v battery. 'Only' problem is that the relay would be actuated whenever the battery is in its normal mode, resulting in a current drain. You'd want to find a very low current relay. Bud
Bud Krueger (TD10855)

Not ignoring you Kieth...was going to get a better picture of the in-line fuse I used. Forgot to do it again today. Try to get that done tomorrow.

Stopping to think about this a little more ...believe I did have a .25amp fuse that "popped" when I had a starter problem a few years ago. (repaired with the ball-pein hammer from tool kit.) I am going to look ...but I'll bet there is a 1 amp in there now?
Haven't had an issue with it drawing current ...and I have tried to start a few times with switch in disconnect mode.

The plug holder came from a friend in the UK that found it for me. It mounted nicely to my battery bracket. I have told a couple people at car show's it's part of my "boost" for the nitros set-up! Had some plug wires on it just for the heck of it to confuse somebody. They don't like me at car shows ;-) but I have fun!

David Sheward

There again, you could disconnect at 12 noon and reconnect at 12 setting required....???
gblawson(gordon- TD27667)

Switch the hot side and just tap the fused clock feed off the switch on the battery side, or otherwise attach to the post. Then nothing but the clock, Radio memory, cell phone charger, or whatever will run off the battery, and everything else goes through the switch. Which is pretty much what David S said.

Fletcher R Millmore

That's the simplest way, FRM. Just requires the relocation of one wire (the clock power lead). Bud
Bud Krueger (TD10855)

Fletcher,(or Bud)

Your solution - I'm afraid I don't understand, although it appears to be clear to Bud so believe me, it is me.

When you say say switch the hot side - what do you mean. I guess you need to spell it our for me. To start it out, my car is neg ground and has the Green knob unscrew to disconnect the battery on the neg. post and the braided neg ground wire to the car battery tray side.

The radio (fused) and clock (not fused but should be I guess) both have a hot power wire that goes to a brown with white wire that goes to terminal A on the control box. This allows both to stay on or be turned on when the ignition is off. The instrument itself is grounded.

So exactly what do I do with the hot wire coming off the clock?


Keith -
"hot side" = not the grounded terminal of the battery.
Since you are trying to split circuits, you have to do it somewhere that is not common to all circuits, so you have to switch the hot side, not the ground side.
Then you take your "constant power" off between the disconnect and the hot Batt post.
So you need to put your disconnect device on the positive post and leave the ground cable from Batt - to body alone. You could use the disconnect you have by reaming out the hole to fit the + post, but it would be much better to get a real switch, can be had for around $20-25. Some of them have a terminal for just this purpose, but it's usually easy enough to rig one.

Fletcher R Millmore

Ok now I understand - thanks. I was getting confused over the word "Switch" as in a Switch you turn off an on and the use of switch to mean change.

I still think Gordon Lawsons replacement clock idea is the best !!! Check the archives under "Clock" Arpil 2010

Steve Wincze

This thread was discussed between 15/08/2010 and 19/08/2010

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