
To clarify things, I have just done this job here below that Spudd has excellently described. As far as I am aware this refers to Nosejob Multiplas that ONLY have an electric boot/tailgate release switch, like mine (no internal tailgate release.)
Here's a tip before you spend out, though:

DON'T REPLACE THE SWITCH! CLEAN IT!
This can be done without dismantling the actual switch. Remove the switch as described below, from the car. Gently pull off the rubber cover and then spray WD40 around the switch and then turn it upside down and tap it on the worktop. Lots of mud and crud will come out. I kept doing this for about 5 mins, flooding it with WD40 and tapping til no more crap came out. You can feel the switch starting to work as you do this.
To test you have fixed it, reconnect the switch to it's electrics while it's in your hand, BUT pull apart the small wire connector near the lock on the tailgate. It is a sensor of some kind. If you don't disconnect this small connector while you are testing the switch, the car will sense the tailgate is open and not allow the switch to work, thus you will think you haven't fixed it!
It is a bit of a fiddle getting the rubber back into the housing, but persevere and you can do it, I promise.

Now then. Is it possible to clean the switch it while it is in situ on the car? Theoretically, I think it is. You can remove the rubber cover easily enough while it is on the car and thus you can get switch cleaner or W40 into it to the switch to flush out the crud. But I am not entirely sure that you will manage to get the rubber back into place without physically having the switch in your hand. But, if you can't you're gonna have to remove it anyway so you haven't lost anything.
Having done the job now, I will certainly have a go at cleaning the switch without removing it from the car next time it seizes up.

I hope that this post has been a useful supplement to Spudd's superb description of the job in hand.

Panda, Myrtle and ably assisted by Steph!
All,
I too had the problem of not being able to open the tailgate on my '54 Multipla.
Following the advice here, established that the microswitch was not working (ie when operated the lock did not open and release the tailgate - there is no fuse to check) i then purchased the microswitch from my local Fiat garage (£63.36 inc VAT - THIS IS TRULY A WICKED PRICE FOR WHAT IT IS :bang: ). It is no cheaper on e-bay.
Follow these instruction to remove old switch and fit new one. .
Allow 1.5 hours.
- Open tailgate from the inside. There is a small metal tab which is part of the lock - the small gap between the lock housing and the lock itself will allow you to put one finger in and push the tab towards the lock. This will release the lock and the tailgate will open.
- Remove the plastic inner panel - 4 phillips screws, one each corner. Pull panel away - there are some plastic retainers that will pop out as you remove the panel).
- Remove the lower plastic moulding - this is the piece on the outside of the tailgate that holds the number plate etc. . Remove the 4 phillips screws around the outside. Then remove the 2 phillips screws on the inside of the tailgate. Then remove the 3 star headed screws just above the number plate. Pull the plastic panel away - two platic retainers will then pop out.
- Remove the 2 star headed screws that hold the offending micro switch in place.
- Dismantle the electric lead
- Re-fit the new switch, connect the lead and test.
- If all OK, then refit the tailgate plastic moulding and inside panel in reverse order of the above instructions.
This is not a particularly difficult job, and believe me, if I can do it, anybody can!!
Hope this helps.
Spudd.