davidgsmith Posted April 20, 2008 Report Share Posted April 20, 2008 (edited) Here's a silly question for a rainy Sunday. When fitting a battery isolator switch, which is the best terminal to stick it on ?? Does it matter? Discuss.... Edited April 20, 2008 by davidgsmith Quote Link to post Share on other sites
ianhoward Posted April 20, 2008 Report Share Posted April 20, 2008 Afternoon Dave If it is the 'Dis-Car-Nect' type isolator, they go on the -ve terminal which I believe is always the preferred terminal for -ve earth cars... No doubt there will be others whose opinion will differ!!! Regards Quote Link to post Share on other sites
davidgsmith Posted April 20, 2008 Author Report Share Posted April 20, 2008 It's the basic screw-off type with a green knob. Bear in mind the TR4 is a positive eath so maybe put it on the positive terminal?? Cheers Quote Link to post Share on other sites
BrianC Posted April 20, 2008 Report Share Posted April 20, 2008 I'm glad you asked that question - I almost asked it a few weeks ago as I'm planning to fit a 'Dis-Car-Nect' type isolator to my TR3A. Lynda's TR4A came with one fitted to the positive (earth) terminal and from what I've been able to deduce from various web sources, it should go on the earth terminal. As I'm a complete electrical dumbo, I will follow this discussion with interest. Quote Link to post Share on other sites
piman Posted April 20, 2008 Report Share Posted April 20, 2008 Hello David, I'm not sure that it really matters. Normally when disconnecting a battery the earth terminal is the one to undo, simply as shorting the spanner to earth when undoing the clamp is harmless. But as the disconnect is just a switch then what is the difference? As it happens I have a disconnect switch in the cabin of my Triumph and that is in the live line (+ve on a -ve earth car) simply so I don't stop the clock (the clock being connected upstream of the isolator). Alec Quote Link to post Share on other sites
Nigel Lay Posted April 20, 2008 Report Share Posted April 20, 2008 I put mine to the -ve terminal (car -ve earth). My logic - probably misplaced - was that if something dropped across the +ve terminal & body it would not short if the isolator was in the off position . I used a key type going through the bulkhead. It's a bit tucked away behind the spare coil and tool box, one advantage of a 2, there is room for a permanent tool box under the bonnet Nigel (with TS952) Quote Link to post Share on other sites
ianc Posted April 21, 2008 Report Share Posted April 21, 2008 Nigel's logic is sound - regardless of whether you have positive or negative earthing, put the isolator in the run to the bodywork (earth). Then, as he says, should one accidentally short the other terminal to the bodywork whilst working on the car (the isolator would, of course, be "off" whilst you are working on the car!), no harm would be done. Ian Cornish Quote Link to post Share on other sites
davidgsmith Posted April 22, 2008 Author Report Share Posted April 22, 2008 Bit scuppered now as the isolator switch will only fit over the negative terminal post. The positive post has a larger diameter so looks like my mind has been made up for me ! Quote Link to post Share on other sites
stuart Posted April 22, 2008 Report Share Posted April 22, 2008 (edited) Bit scuppered now as the isolator switch will only fit over the negative terminal post. The positive post has a larger diameter so looks like my mind has been made up for me ! You could always drill it out to suit or convert to neg earth. Stuart. Edited April 22, 2008 by stuart Quote Link to post Share on other sites
Guest colinTR2 Posted April 29, 2008 Report Share Posted April 29, 2008 David I have a simple version with the removable key fitted into the +ve side of the battery on my 2. It's been there for around 15 years with no problems at all. I fed the battery cable through the bulkhead and fitted the disconnect close to the steering column where it can only be seen if you are a contortionist. getting the key in first time is fun, but you soon get the hang of it! best of luck Colin Quote Link to post Share on other sites
davidgsmith Posted April 29, 2008 Author Report Share Posted April 29, 2008 Hi Colin, which version of the disconnect unit did you use? I think I would feel better having the unit out of sight. Any chance of a photo? Thanks, David Quote Link to post Share on other sites
Guest colinTR2 Posted April 30, 2008 Report Share Posted April 30, 2008 David, I don't know what mine is called but you get a good view of it in the photo, if this all works. I've not put pictures on the forum before!! I seem to have uploaded 435K, previously I saw it as only around 100K. Let's see what happens? Quote Link to post Share on other sites
Guest colinTR2 Posted April 30, 2008 Report Share Posted April 30, 2008 Ok, I see, if you click on the line then the photo downloads. Not quite what I intended! Can I then delete to free up more memory? How does one get the photo onto the reply like most others? Some advice please. Anyway, hope this helps. I am off on holiday to Italy tomorrow morning and wanted to do this before we go. cheers Colin Quote Link to post Share on other sites
davidgsmith Posted April 30, 2008 Author Report Share Posted April 30, 2008 Thanks Colin, I managed to have a look at the photo. Much appreciated. Have a great Holiday David Quote Link to post Share on other sites
john.r.davies Posted May 1, 2008 Report Share Posted May 1, 2008 Interesting discussion. In contrast to the above consensus, the FIA demands a cut-out on the side of the battery that supplies the race car with power, not the earth side. I don't know why they chose that, as using either seems logical, if the battery terminal that is isolated cannot touch any metal parts, but anyway. John Quote Link to post Share on other sites
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