keith1948 Posted July 30, 2018 Report Share Posted July 30, 2018 Just thought I would share some information regarding voltage stabilisers. Both Moss and Rimmers specify the part number 128484 for both TR4 and TR4A. However this stabiliser is for positive earth only vehicles (i.e. original TR4 spec). As such they will not work on the TR4A. Instead you should fit the TR5 unit part number 148876A which is for negative earth cars (TR4A and later). This is because these later units have solid state internals and need to be connected with correct polarity. The original stabilisers had a bimetal strip with a heating wire coiled around it. Voltage was regulated by the rapid make and break of the bimetal strip. Didn't matter whether positive or negative earth for those types. Would work either way. Earlier Moss solid state units had part numbers 131-555 for negative earth and 131-556 for positive earth if you have one of those. This all came to light this morning when I turned out the spares in the boot to find that my spare voltage stabiliser was a positive earth rather than negative for my 4A. Also discovered the spare spark plugs had gone rusty and were not the same as in the car and the spare radiator cap had disintegrated. Time for a spares spring clean I think to see what other junk I have been driving around with in the boot. Keith Quote Link to post Share on other sites
monty Posted July 30, 2018 Report Share Posted July 30, 2018 Just thought I would share some information regarding voltage stabilisers. Both Moss and Rimmers specify the part number 128484 for both TR4 and TR4A. However this stabiliser is for positive earth only vehicles (i.e. original TR4 spec). As such they will not work on the TR4A. Instead you should fit the TR5 unit part number 148876A which is for negative earth cars (TR4A and later). This is because these later units have solid state internals and need to be connected with correct polarity. The original stabilisers had a bimetal strip with a heating wire coiled around it. Voltage was regulated by the rapid make and break of the bimetal strip. Didn't matter whether positive or negative earth for those types. Would work either way. Earlier Moss solid state units had part numbers 131-555 for negative earth and 131-556 for positive earth if you have one of those. This all came to light this morning when I turned out the spares in the boot to find that my spare voltage stabiliser was a positive earth rather than negative for my 4A. Also discovered the spare spark plugs had gone rusty and were not the same as in the car and the spare radiator cap had disintegrated. Time for a spares spring clean I think to see what other junk I have been driving around with in the boot. Keith Wouldn't you think Moss & Rimmers could get their part numbers correct by now! Quote Link to post Share on other sites
RogerH Posted July 30, 2018 Report Share Posted July 30, 2018 I think the problem is that all TR4 and most 4A were/are positive earth. so their number is correct. many have now been changed to Neg earth so you need the TR5/6 item Roger Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 30, 2018 Report Share Posted July 30, 2018 (edited) Just thought I would share some information regarding voltage stabilisers. Both Moss and Rimmers specify the part number 128484 for both TR4 and TR4A. However this stabiliser is for positive earth only vehicles (i.e. original TR4 spec). As such they will not work on the TR4A. Instead you should fit the TR5 unit part number 148876A which is for negative earth cars (TR4A and later). This is because these later units have solid state internals and need to be connected with correct polarity. The original stabilisers had a bimetal strip with a heating wire coiled around it. Voltage was regulated by the rapid make and break of the bimetal strip. Didn't matter whether positive or negative earth for those types. Would work either way. Earlier Moss solid state units had part numbers 131-555 for negative earth and 131-556 for positive earth if you have one of those. This all came to light this morning when I turned out the spares in the boot to find that my spare voltage stabiliser was a positive earth rather than negative for my 4A. Also discovered the spare spark plugs had gone rusty and were not the same as in the car and the spare radiator cap had disintegrated. Time for a spares spring clean I think to see what other junk I have been driving around with in the boot. Keith As the person who wrote the electrical section of that catalogue in the late 1980's, we only listed the 128484 as it was available as an original item from the factory. The use of original part numbers indicated original quality product. Addition of a Z suffix usually meant it was an aftermarket/budget item usually aimed at the price competitive MG market. I see where you arrived at now. 128484 is OK in its original design/construction to do both +ve & -ve earth cars as you have correctly pointed out - - as in TR4/4A,Spit1/2, GT6 1 etc The rub comes as Moss are now supplying a solid state item that is suitable only for +ve earth vehicles under the original 128484 part number which we know did both earthing types. They need to add the 148876 pt no to their TR4/4A listing for -ve earth vehicles if they intend to keep supplying the solid state polarity sensitive item under 128484. Perhaps Moss Europe should adopt the two Moss USA part nos (131-555 & 131-556) and superscede the 128484 & 148876/BHA4602 pt nos to them. They can then sell any old item as they have not hinted that the items are to original quality by the use of the original part number. This addition of +ve earth and -ve earth types is in the MGB catalogue https://www.moss-europe.co.uk/shop-by-model/mg/mgb-c-v8/electrical/gauges-instruments/gauges-cables-mgb-1962-76.html Note 148876 does have different terminals to error proof its fitting on the modern cars. one male and one female connector. and if my memory is right 128484 had two male connectors - step in here those with more knowledge. Ho Hum Peter W PS Have sent error log to Moss Europe to review catalogue information. Edited July 30, 2018 by BlueTR3A-5EKT Quote Link to post Share on other sites
keith1948 Posted July 31, 2018 Author Report Share Posted July 31, 2018 Hello Roger. Original wiring diagram for TR4 shows positive earth whereas original wiring diagram for TR4A shows negative earth. As you say many people have changed their TR4's to negative earth. Thanks Peter for your detailed reply. I have a 131-556 positive earth stabiliser that has both male and female connectors on both terminals. The one on the car from 1965 that is still working ok has male spade connectors. So I guess I need to ask myself the question if it has been working ok for the last 53 years do I really need to carry a spare or at that age might it pack up at any moment. Who knows? Keith Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 31, 2018 Report Share Posted July 31, 2018 Ah. ......the bath tub curve of reliability Quote Link to post Share on other sites
stuart Posted July 31, 2018 Report Share Posted July 31, 2018 Hello Roger. Original wiring diagram for TR4 shows positive earth whereas original wiring diagram for TR4A shows negative earth. As you say many people have changed their TR4's to negative earth. Thanks Peter for your detailed reply. I have a 131-556 positive earth stabiliser that has both male and female connectors on both terminals. The one on the car from 1965 that is still working ok has male spade connectors. So I guess I need to ask myself the question if it has been working ok for the last 53 years do I really need to carry a spare or at that age might it pack up at any moment. Who knows? Keith And back to the old chestnut of 4A`s being neg or positive earth. We have been here before and its seems a lot were positive earth Stuart. Quote Link to post Share on other sites
silverfox4 Posted April 27, 2020 Report Share Posted April 27, 2020 Some research raised this thread, so pertinent to bump. My 4A might be on of those, as the voltage stabilizer has all male terminals (per the 128484 noted above). I have now purchased the solid state version and the instrument terminals "I" are female and the Battery "B" are male. To use this VS, do I have to change the instrument connection in the loom or forego the solid state version and stay with what I have for now. Also I cant say whether the instruments are reading high or low at this point. Cheers, Alf Quote Link to post Share on other sites
RogerH Posted April 27, 2020 Report Share Posted April 27, 2020 I see in the Moss webCat that for 4/4A they quote BHA4602 for Negative earth. But use the same part number in the tr6 for positive earth. I bought one three or four years ago and it was a cube shape with fly leads and worked well. Be careful out there. Roger Quote Link to post Share on other sites
stuart Posted April 27, 2020 Report Share Posted April 27, 2020 7 hours ago, silverfox4 said: Some research raised this thread, so pertinent to bump. My 4A might be on of those, as the voltage stabilizer has all male terminals (per the 128484 noted above). I have now purchased the solid state version and the instrument terminals "I" are female and the Battery "B" are male. To use this VS, do I have to change the instrument connection in the loom or forego the solid state version and stay with what I have for now. Also I cant say whether the instruments are reading high or low at this point. Cheers, Alf Just check that yours is outputting 10V and if it is then stick with it as the originals rarely fail. Stuart. Quote Link to post Share on other sites
stillp Posted April 27, 2020 Report Share Posted April 27, 2020 It used to be possible to buy an adaptor that was a male push-on at both ends. Maybe one of the auto-electrical sellers has them? Pete Quote Link to post Share on other sites
silverfox4 Posted April 27, 2020 Report Share Posted April 27, 2020 Thanks all, I'll try the 10v check then, but probably later as there is more important stuff to do at the moment. For now I am inclined to leave it until we are driving. Cheers, Alf Quote Link to post Share on other sites
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