I've registered about 12 , UK & German , over the years for various people . It's easy enough to do yourself but time consuming & you need the patience of a saint. It's easier to use an gestoria for the paperwork part as he's doing it all the time.
All we've ever done is take the vehicle to the ITV ( mot ) station & tell them that you want to change on to spanish plates . They'll do the inspection & ITv & assuming it's all ok , you'll receive the 'ficha tecníca' ( log book ) in the afternoon. ( But not on Fridays as the Madrid office doesn't work after 2pm ! )
Once you have that you can go to your local 'Hacienda ' ( local tax office ) & pay the road tax using the 'numero de bastidor ' ( VIN number ) based on engine size , Co2 emissions.
From there it's to ' El Trafico ' ( similar to a DVLA office ) which in my case is in Murcia, 80kms away. Here you get a form fill in all details & await your number being called. Assuming that there is no import tax to pay as you are newly resident & with a new 'padron' ( This shows that you are registered as renting/owning at the address given. Sort of similar to being on the electoral roll in the UK ) , after a short while you'll receive the Ficha Tecníca back with a reg. number printed on it. You can now go & get some number plates.
If there is tax to pay you'll have to go to the local Hacienda, which in Murcia is a 5 min walk from El trafíco. Once you've got in, & the security is worse than an airport you'll be given a number which when called you go to a desk to sort out how much tax is payable. Then you take another number which when called allows you to pay the tax at the bank which is within the buiding. Once paid , now I know you've nearly lost the will to live but struggle on as it's near the end, take another number which when called you go to the desk, present paperwork & payment receipt & they'll stamp it all. You can now return to El Trafíco & complete the registration !
All the above can & will vary from Region to region & day to day depending on if you are unfortunate to stumble upon the miserable barsteward whose sole intention is to muck you about & believe me they exist in large numbers ! We found that it was cheaper to use a gestoria after we'd done the ITV as they don't have to queue,Just slap the pile on the desk & as long as it's before 11am it's completed by 2pm.
Using an gestoria allows you to pay any tax due in his office as they are licensed by the government & in addition have access to the Government website that gives used car prices for every vehicle upon which the tax is based.
This is a list of vehicles ;
www.boe.es/boe/dias/2010/12/27/pdfs/BOE-A-2010-19848.pdfFind you vehicle, or nearest to it, note price then go here ;
www.aeat.es/AEAT/Contenidos_Comunes/Ficheros/Informacion_Institucional/Campanias/IMPUESTO_ESPECIAL_SOBRE_DETERMINADOS_MEDIOS_DE_TRANSPORTE/Otros_Servicios/pdvu2006.pdfscroll down to anexo IV & work out the depreciation . This will give you the figure on which the tax is based.
Remember that just because you paid £500 for a '97 nissan terrano inthe Uk it will be valued as if it was spanish & if it's rhd there's no reduction for the fact that it's near on worthless !
Also to bear in mind is if the vehicle is heavily modified . you'll have a job to register it & it'll probably need an inspection Or certificates of fitting ( certificados de montaje ) for any additions.
all additions/ alterations are noted on the Ficha tecníca, unlike the UK but similar to Germany. Tyre sizes,wheel diameter, auto-box, sun-roof, towbar, bull bars, additional driving lights, etc;etc;etc !
If it's not on the log book it's not legal. Any change of wheels , ride height , bodywork, has to be homologated At a cost the same as an mot , about 48€.
They have some demented fascination with the output of headlamps , which musn't exceed 75 candle power. Even a UK Discovery fitted with standard LR driving lamps will fail as they are to powerful for the spanish regulations.
Good luck ! ;D