fraronni Posted October 1, 2010 Share Posted October 1, 2010 Hello. I have a British airborne trailer type: "Trailer, Lightweight, 10 CWT, Airborne / Amphibious". During the restoration of this I found something with the electrical wiring harness I have wondered about. It seems that none of bulbholders have grounding in the shelf. All are double contact bulbholders, and acts as if power and ground going into one and out of the second of these? To get this to be correct, it must then have been a special light bulbs for this type?? What is the correct bulb for this type of wiring, and where can you buy this?, Hope someone can give me an explanation for this, and if my observations are correct? If anyone also know of where one can buy new cables in the old style for this trailer, this had been a bonus! regards Frank Quote Link to comment Share on other sites More sharing options...
antarmike Posted October 1, 2010 Share Posted October 1, 2010 (edited) Presumably the bulbs you refer to are SBC not the more normal SCC. Nevertheless you should be able to get them at any good auto-elctrical outlet. SBC now called BA15d http://www.twenga.co.uk/dir-Supplies,Bulb,BA-15D-bulb SCC known as BA15s http://www.twenga.co.uk/dir-Supplies,Bulb,BA-15S-bulb-0110526 http://www.thetoolboxshop.com/ab382-12v-21w-382-scc-single-contact-equal-bayonet-automotive-bulb-734-p.asp System you refer to is also known as Insulated return. It has various advantages. It is widely used on Fuel tankers, since if a wire chaffs on the chassis , and the insulation is worn away, there will be no spark or flash if wire touches chassis since the chassis is "floating" and offers no return path for the current. Insulated return also minimises Galvanic erosion (or Corrosion), that happens when negative side of battery is connected to chassis which is the return path( negative earth) , and happens even more badly if the Positive terminal is grounded to the chassis, (Positive Earth) Double contact bulbs SBC are widely used in Rubbolite lamps (flexible lamps) because having a rubber body, they rely on a seperate earth wire from each lamp. Edited October 1, 2010 by antarmike Quote Link to comment Share on other sites More sharing options...
fraronni Posted October 2, 2010 Author Share Posted October 2, 2010 (edited) Hello antarmike! Thanks for a very detailed and very explanatory reply. Had never encountered this type of wiring before, but now I've got the explanation for this! Nice to have good answers, when one is stuck on something! Regards Frank Edited October 2, 2010 by fraronni Quote Link to comment Share on other sites More sharing options...
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