I just bought a pair a GFS P90s, but the neck pick up is dead. GFS have a KwikPlug connection, so I can swap the pick ups easilly a rule out my messy soldering.
 
I ordered these to be delivered to my cousin in California, who was visting my family in the UK the same time as me a month later, and now I have them back in Viet Nam.
 
To get a replacement, I have to wait for an American friend to go back to the US, and have a new one sent to their US address, I don't want to ask as much as having them post the faulty one when they are on holiday stateside. And this could be nearer Christmas. For the cost of a GFS pickup, I'm wndering what could be wrong
 
KwikPlug female needs re-soldering?
Coils wire come loose from the connection wire?
 
Anyone made/fixed pick ups before?
 
(If that wasn't bad enough, I snapped the high e-string with the back and fourth, and I can't get my set in the Vietnam, but I have found a single in a set that is a close match)
 
 
So 

Since you got a pair of these pickups, I am assuming that you swapped them to verify that it is the pickup and not the guitar wiring.
 
I am not familiar with the "KwikPlug" or if you can slide the case apart easily, but most issues occur at solder joints (highest resistance and point of failure) than in a "wire." The guts of that may be potted, and is essentially a spool of wire on magnets, but the ends (if it can be coil split will have 4, otherwise 2) should be easily accessible with the case opened (many with covers will slide off). Do not dig into the windings in any way, or you could break the wire; and beware of slack concerns (you may not have much) if you try to slide that case apart.
 
It is highly unlikely to be the coil, but more a joint from coil(s) to kwikplug, or the kwikplug to its socket (but on the pickup side if the other pickup works in that socket).
 
When troubleshooting pickups, do not worry to retune strings. The low strings have the most output anyway, and they only need to be tight enough to vibrate to test continuity (even just the A string will work for this, leave the rest slack and pulled behind the neck (I use a piece of string for this behind the heel)).

A dead pickup means the wrap wire or connection cable is broken.

So could be the plug, could be where the cable joins the wrap wire at the pickup, could be the wrap wire itself is broken inside the pickup.

Fault finding requires a meter that measures resistance. If you have one you could check the cable between the solder points on the pickup and the plug terminals. If either of those connections reads open circuit then the problem’s in the cable. If it doesn’t read open circuit the problems almost certainly a break or short circuit in the wire wrapped round the pickup.

There’s an awful lot of that very thin wire, and as the pickup’s new I’d look to getting it changed under warranty rather than trying to repair it.

So it's is basically one of these two issues.
 
KwikPlug female needs re-soldering?
Coils wire come loose from the connection wire?
 
I have swapped the pick ups Mattelus, so it's definitely the pick up. The KwikPlug is a four point mini jack, with the female on the pickup. I've messaged GFS, so I haven't attempted the opening it's case yet.
 
No meters unfortunately TLW, and the small plastic casing means nothing is exposed until I try t remove it. Being in Vietnam, means I'm looking at January before I get a replacement. I can't warrant the cost postage, so may as well right it off and attempt to fix. Worse case scenario I buy a replacement. GFS aren't expensive at $30
 
https://www.guitarfetish....ckel-Case_p_21785.html
 
 
 
 

I can only offer encouragement ...
 
I put a set of GFS Mean 90s (not connectorized) in an LP a few years ago.  Awesome pickups!!
 
 

I've had a small play with just the one pickup, and so far I'm happy with the change. So I'll persevere with them.
 
BTW I only went for the Dream over the Mean, because they don't do the Mean in Nickel. I think they used to, be made a batch with the Dream and the previous haven't been re-made

At least I worked out today that the D'addario unwound strings are all the same. Because of the humidity here, these die quickly. My wound stings are chromes and the humidity desn't touch them. I can't get my strings in Viet Nam, as they like super bright and light.
 
I as able to replace my B and E stings with unwound G and B strings. I hadn't thought of that before

After seeing that picture, I would suspect the kwikplug, which seems to be glued to the back. Taking the lid off may buy you nothing, since it seems they soldered the plug outside the case, then glued it down. Assuming this passed QC, the female pin sockets may be bent or sprung just enough not to make contact.

Sans a meter, if any sockets are obvious but you cannot get to them to straighten, you might be able to bridge the pin gap by wrapping aluminum foil on the male pin(s). One wrap and leave it a smidge too long. This may not be feasible since the connector looks tiny.

Agreed, the connector is too small with too many contacts to try messing with.
 
I found this pic, so the case comes off as I thought.  

Hmmm, does that cover come off though? It looks like it has screws from the back (which are inaccessible). *If* that snaps off, all of your solders and pins are right there.