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keith1948

voltage stabilisers for TR4 and 4A are different

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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

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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!

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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

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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 by BlueTR3A-5EKT

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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

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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.

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