Changed to new fusebox and smoke appeared

Hi,

Struggling to finish a 9 year and 9 month resto of a mk1 GTi.

Had a problem with my old fusebox that had seen some water in the past so decided to opt for a newly produced one.

Drove the car out of the garage and removed the connectors for the old one taking plenty of pictures during.

Plugged the new fusebox in and checked that all was connected according to the old fusebox.

Connected the battery and I hear (I imagine) the sound of the wiper motor going into park mode. Wiper motor is a mk2 one that I installed and tested about two weeks ago.
At the same time the electrical smoke of horror starts to appear under the dash. Quick disconnect battery and air out the car.

Now I've tracked down the melted wire being the D22 fusebox wire, ground for "22- brn - windscreen wiper motor pin 31, and to main battery earth jumper on lighting loom" (thanks rubjonny for posting the pinouts)

The pin for D22 on the white connector got hot and is now in two pieces. Possible it was bad/worn/damaged to begin with. D22 connects to an earth connector where 4 wires join the battery terminal ground (?) (Seen in pic)

Looking at the new fusebox, no fuses burned but the relay 17 has melted plastic around pin 1 on the fusebox and pin 85 on the relay. Relay is no 17 and on relay position 8 on fusebox for Load reduction/x-relief. Relay looks like the original one so has seen better days. That the issue is connected to the load reduction seems logical since it happened just after connecting the battery + terminal.

Any tips on what may be the culprit? Everything worked before switching to the new fusebox. Any help is very much appreciated. Had planned for MOT this week but that'll have to wait 😂😬


 

Okay so I did some more digging and I have a theory:

Fitting the old relay 17 to the fusebox, leg 85 on the relay loosened and jammed up into the relay internals coming into contact with the inner relay body and thereby also leg 30 on the relay which is live (?) when the battery is connected.

The short went from leg 30 +live feed to the leg that was still in contact with the fusebox and through fusebox and exited via D22 which is a ground pinout then to body and melt-a-monium started.

The ground connected to D22 on the fusebox is the only melted one I could find.

Figs show the damaged relay 17 (original relay) and some damage to the fusebox plastic where the relay leg 85 was stuck.

Anyways gonna repair the ground wire and connector when the pin I ordered arrives and I will be careful to connect the bare minimum fusebox connectors to check to see if the problem is solved.

If it ain't broke, don't fix it. But if you try and fix it best take care to ensure that age hasn't degraded the parts you re-install.