upgrade to mk3
You can go to any decent auto parts store and buy bulk wire. Bigger gauge will not hurt, but you don't need it to big. Prob 16 or 18 ga. I have had alts go bad quickly especially if they are rebuilds. Also keep in mind depending on the car there is a diode that can go bad as well. I can't remember if this wire goes through the fuse box first before it makes it to the cluster. If it does that can also bring those connections into suspect. What car are you working on?
1983 Rabbit GTi- Alternator was changed over the summer, battery last year.
My mechanic had the dash and gauge cluster apart to change blower motor and odometer gear so maybe the blue wire was messed with.
I am bringing it back to him this week.
When I looked at the alternator, it looks as if the blue wire has been cut off. I wanted to put it up on ramps to get a better look but I am home sick today.
I have changed 2 alternators and 3 batteries in this car....
Always had a problem with not getting enough volts...
Maybe its the blue exciter wire OR the alternator is faulty.
IF the wire is not connected at the alt, start there first and reconnect. It is pretty straight forward to pull a new wire into the car. I'm not sure what your skill level is with working on cars, but it's not a bad job. I dont think the those had a diode. I have also had loose connections at the gauge plug. Low hanging fruit, reconnect the wire.