View Full Version : TR2/3/3A TR3A battery quick-disconnect

05-02-2007, 05:48 PM
Just tried installing the "battery cut-off switch", Moss 145-795. Seems to be good quality, but sure installs weird.

It's sized for the negative post, so can't go on the woven cable if you have a positive ground system.

Installation causes the negative cable to end up "vertical" instead of horizontal at the battery end.

With the positioning of the cut-off switch on the negative cable, the cable needs to go between the battery and the battery hold-down "stump". That's really tough to use - as you can't pull the disconnect the way it's set in there. Seems more trouble to try to disconnect the switch than to just loosen the original battery clamp nut.

Has anyone used that disconnect switch on a TR3A?


05-02-2007, 06:11 PM
There was a recent post on these. I had one that broke where the metal is thin and the unit fell into my steering shaft an almost caused me to hit a curb at speed. Others chimed in of problems also. The recommendation was to take the strain off the unit by supporting the ground cable. I would not have another one.

05-02-2007, 06:35 PM
I have one on my 3A but my ground cable routes up to the firewall not down like yours.

Don't they disconnect by turning the knob 1/4 turn CCW?

05-02-2007, 06:37 PM

Here is the thread.

05-02-2007, 06:55 PM
Peter - Sorry - the pic I attached was from the Moss catalog. In the positive ground car like mine, the cut-off has to attach at the battery negative post, then to the red cable in my car:


When in use, you disconnect the battery by unscrewing the green knob, then pulling out the male part of the switch (attached to the cable) from the female part (attached to the battery post). It's not really a "quick" disconnect - it just allows you to skip having to find a wrench to loosen the battery post nut.

So with the right angle created when you attach the red cable to the cut-off switch, there's hardly any room for the cable to run - except between the voltage regulator box and the battery hold down tab. Imagine the pic in my first post, but using the red "starter button" cable instead of the woven ground strap. Not much room there, especially as the cable is quite stiff.

I'm just wondering if anyone has successfully attached this switch on a positive ground TR3A.


05-02-2007, 07:07 PM
Aloha Tom,

I have one installed in my TR3 and it looks like yours. The one I have works like Peter's, twist the green knob CCW and it electrically disconnects. After a "smoke from the dashboard" incident a few years ago in a different car, it seemed like a good safety accessory.

05-02-2007, 07:39 PM
Over the last 10 years, I've used about 20 of these quick disconnects and have never had a problem. I've also never seen one that you have to completely unscrew. I just turn the ones I have about 1/4 turn and the battery is disconnected. I'm presently using them in 6 different cars, 2 of whick are TR3s, but both TR3s have been converted to neg. ground. When working on LBC, I think they are great. Saves me alot of sparks and smoke.

05-02-2007, 07:41 PM
Put a meter on yours and I'd bet that just a 1/4 turn disconnects the power. You need to turn it just enough so that the threaded portion that goes through the bottom piece hits the insolator. No need to take the knob and shaft off. My knob even says turn 1/4 turn to disconnect.

05-02-2007, 08:09 PM
Hmmm - top of the green knob reads "off" with arrow pointing left, and "on" with arrow pointing right, and "keep clean and tight".

The green knob is the top of a screw; the screw goes *through* a hole in the male part which is clamped by the original cable clamp. So unless the screw is fully removed from the hole, you can't pull the male part out of the female part. Seems quite strong.

But I'm basically asking if anyone is using this on a positive ground TR3A. It's described as "for negative battery post", so it has to go on the passenger side of the battery on a positive ground car. When it's on that negative post, there's hardly enough room to pull the male part out of the female part when you try to disconnect, as it's crammed between the voltage regulator and the battery hold down tab.

Edit: if the screw isn't fully removed from the hole, it's still touching the male part, so the circuit is still active.

Thanks again.

05-02-2007, 08:16 PM
Hello, Tom, I've used one of these on my positive ground TR3 for the past 3 years: here's a pix https://i125.photobucket.com/albums/p52/mrv8q/IMG_0556.jpg
I like it so much, I got one for my TR6; hopefully I'll be able to use it one day!
I usually turn on the headlights, crank the disconnect until the lights go out, and then turn off the lights.... hope that helps!

05-02-2007, 09:05 PM
Kevin - yes - that's exactly what I was looking for. Thanks!

For some reason the cable end (the blue cable in your pic) is really tough to pull out of the slot when the green-knob screw is removed. I can't get my hand onto it firmly enough to get a good grip - the voltage regulator gets in the way.

I also think the style you and I have is slightly different from the "1/4 turn CCW to disconnect" one PeterK is describing.


05-02-2007, 09:08 PM
If you look at Kevin's picture, you can see the white plastic insulator that sits between the top and bottom 1/2s. The only electrical connection on most of these cut-offs is the screw attached to the knob. So when you screw it all the way in, the connection is made after it passes the insulator into the bottom 1/2. TO break the connection, just unscrew enough so that the screw doesn't touch the bottom 1/2 as it is insulated above.

Yours (Moss) must be made differently if you have to remove the screw. Sorry if I misunderstood but I've never seen one that works like that.

Looks like Kevin's terminals might be on the rear of the battery box so he has clearance.

Mine is just like Kevin's. Turn 1/4 CCW as described above.

05-02-2007, 09:21 PM
For some reason the cable end (the blue cable in your pic) is really tough to pull out of the slot when the green-knob screw is removed. I can't get my hand onto it firmly enough to get a good grip - the voltage regulator gets in the way.I also think the style you and I have is slightly different from the "1/4 turn CCW to disconnect" one PeterK is describing.

Hmmm, I'm a little lost here, Tom.... not sure why you want to pull out the negative cable? I just unscrew mine enought to cut the power; never have to do anything else. Mine are not the high-priced MOSS items; just the cheapie $2.95 one the guy sells on eBay... glad to be of some service!

05-03-2007, 06:45 AM
OK - I'm an idiot.

So we're saying I don't need to remove the green-knob screw? I just need to turn the screw 1/4 turn and the circuit is cut?

Argh ... never would have thought of that. Had been thinking that the purpose of the disconnect was to allow removing the cable without using a crescent wrench. I figured that as the screw was still going through the hole the circuit was still complete.

Chain me to my wheelchair guys!
Tom a/k/a braindead