muddyplugger Posted August 11, 2006 Share Posted August 11, 2006 My battery isolator switch is my main 'anti-theft sysem' on the defender. I am now attempting to bypass this for a permanent suppy for the Radio (I hate reprograming it every time), and I note I have wired my isolator switch to the negative terminal. Why did I do this I asked myself? Answer = I know nothing about electrics in the first instance, and my Dad always told me that it is safest to remove the negative terminal when working on the car, prevents 'sparks' incase of spanner grounding. So my befuddled brain obviously said isolate the negative terminal. It got me thinking (dangerous when I dont really understand the subject), but surely the isolator should be fitted to the positive terminal? For one it would then be possible to bypass it with one wire for my auxillary needs! Other reasons?: When wired to the negative, there seems to be a residual voltage that takes a while to dissipate once turned off. Is this bad?? If I try to start the vehicle with isolator switched off, does the alternator try and 'draw' current from the battery? but has no way back? I have done this accidently and is has occasionally made a few loud thunking noises! Is this possible? Does it really matter which is isolated?? I apologise for this being a bit of a soft topic. Quote Link to comment Share on other sites More sharing options...
western Posted August 11, 2006 Share Posted August 11, 2006 Isolate the +ve terminal, for your radio just go straight off the battery +ve, then you can have the radio on with the ignition off. Quote Link to comment Share on other sites More sharing options...
Happyoldgit Posted August 11, 2006 Share Posted August 11, 2006 There is a battery isolator / anti theft device that fits on the battery + terminal and has a knob which when removed disconnects the battery. There is a version whish has a fused low current permanent supply for radios etc too. Quote Link to comment Share on other sites More sharing options...
geoffbeaumont Posted August 11, 2006 Share Posted August 11, 2006 I'd have thought isolating the negative would be a bit to easy to bypass if you're using it as an imobiliser - just connect the battery neg to a bit of steel bodywork and off you go. Quote Link to comment Share on other sites More sharing options...
western Posted August 11, 2006 Share Posted August 11, 2006 There is a battery isolator / anti theft device that fits on the battery + terminal and has a knob which when removed disconnects the battery. There is a version whish has a fused low current permanent supply for radios etc too. That's this one dis-carnect Quote Link to comment Share on other sites More sharing options...
Happyoldgit Posted August 11, 2006 Share Posted August 11, 2006 ^^ That's the one. Quote Link to comment Share on other sites More sharing options...
rtbarton Posted August 11, 2006 Share Posted August 11, 2006 I had one of those discarnect things on my landy, but I took it off because the contacting faces corroded and because they mate by pressing together rather than with a wiping action they didn't self-clean. Quote Link to comment Share on other sites More sharing options...
Happyoldgit Posted August 11, 2006 Share Posted August 11, 2006 I've got one on one of my cars and have found it ok but like all electrical / battery contacts it does need to be kept clean and corrosion free. I like to keep my battery terminals smeared in petroleum jelly or that red ant corrosion gel anyway. Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted August 11, 2006 Share Posted August 11, 2006 It sounds like you're not totally disconnecting the earth, if you're getting any kind of noise at all when you try to start it while it's disconnected. Electrically, it doesn't matter which terminal you isolate but as was said earlier, it's easier to bypass (if you know what to do - how many thieves carry a multimeter?). The method I've seen for car stereos etc is to put a fuse in parallel with the isolator switch. It can still draw <1A for the radio etc but if you try to start the car with the switch off, you blow the fuse (and lose all your presets!) but turning the switch means the car will start again and you're not disabled permanently. Quote Link to comment Share on other sites More sharing options...
muddyplugger Posted August 11, 2006 Author Share Posted August 11, 2006 It sounds like you're not totally disconnecting the earth, if you're getting any kind of noise at all when you try to start it while it's disconnected Thats what I assumed as it only happens very occasionally. I think a quick re-wire to the positive in the morning is called for. Quote Link to comment Share on other sites More sharing options...
David Sparkes Posted August 12, 2006 Share Posted August 12, 2006 If your battery has tapered posts, rather than flat plates with holes in, the posts are different sizes. Obviously, I don't know how you are connecting to the battery, but if your rearrangement involves moving something from one tapered battery terminal to the other, you need to be aware of this size difference. The clamp pictured earlier could be described as 'wrap round, with a side bolt'. The simpler clamps of this style, where the wires are attached to the clamp with screws, are marked Pos and Neg for this reason (the difference in post size). HTH Actually, I hope the caution is unnecessary :-) Quote Link to comment Share on other sites More sharing options...
rtbarton Posted August 12, 2006 Share Posted August 12, 2006 If your battery has tapered posts, rather than flat plates with holes in, the posts are different sizes.Obviously, I don't know how you are connecting to the battery, but if your rearrangement involves moving something from one tapered battery terminal to the other, you need to be aware of this size difference. The clamp pictured earlier could be described as 'wrap round, with a side bolt'. The simpler clamps of this style, where the wires are attached to the clamp with screws, are marked Pos and Neg for this reason (the difference in post size). HTH Actually, I hope the caution is unnecessary :-) Good thinking Batman. Mine was actually designed to fit on the -ve post and had a blue knob, the one in Vehicle Wiring Products Catalogue has a green knob, and there is no mention of which post it fits on. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted August 12, 2006 Share Posted August 12, 2006 As John said, to the pos terminal, with a bit of small wire with a fuse across the 2 terminals of the isolator to run the radio. Mo Quote Link to comment Share on other sites More sharing options...
muddyplugger Posted August 12, 2006 Author Share Posted August 12, 2006 Obviously, I don't know how you are connecting to the battery, but if your rearrangement involves moving something from one tapered battery terminal to the other, you need to be aware of this size difference.The clamp pictured earlier could be described as 'wrap round, with a side bolt'. The simpler clamps of this style, where the wires are attached to the clamp with screws, are marked Pos and Neg for this reason (the difference in post size). I have noticed this today, as I swopped it over! Obviously the isloator switch is suited to the neg terminal, but it did go on the postitive (with some persuasion!) For the radio, actually routed a fused wire direct from the battery. As I frequently forget that I have the isolator key on my key ring when I start the car. BUT, if this switch is supposed to be on the neg, then I'd better think again. Mind you it hasn't set alight yet. [/crossfingermodeon] Quote Link to comment Share on other sites More sharing options...
02GF74 Posted August 14, 2006 Share Posted August 14, 2006 and my Dad always told me that it is safest to remove the negative terminal when working on the car, prevents 'sparks' incase of spanner grounding. So my befuddled brain obviously said isolate the negative terminal. the same is true if you discconnect the +ve terminal surely? (unless you are running the alternator whcih you shouldn't be!) Quote Link to comment Share on other sites More sharing options...
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