The wiring on a 2a is pretty simple. This means that since getting a new loom made is fairly expensive, it is likely that getting an electrician to "just make you a loom" is likely to cost no more although the difference is not likely to be great. But since the major cost is labour, and the loom maker is probably more experienced at it, the specialist loom maker is likely to be cheaper. The people who make looms pretty much make them to order, so modifications to suit your Holden motor would probably not cost any different. You may have the choice of a lower price by using modern rather than original materials, but as I said, labour is the major cost so I would not expect a big difference in cost.
Unless you are looking to originality (and the Holden motor suggests you are not) the original wiring can be significantly improved, mainly by putting in a few more fuses plus headlight relays, and regardless of which way you go you should consider adding wiring for radio, UHF, telephone, driving lights, reversing lights, hazard lights, interior lights, and anything  else you can think of that you may need in the future
				
			 
			
		 
			
				
			
			
				John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
			
			
		 
	
Bookmarks