Temp guage not working after m20b20 to m20b28 swap

[liamobzr]

Checked the zone wiki and it said the following

" To test, first unplug the C101 and earth pin 4 (brown/purple wire). Now if you switch the ignition on, the gauge should go to full hot. If it does, repeat the test at the brown plug by removing the cable from the brown plug, and earthing the terminal with a piece of wire (for older cars with two-pin terminals, just bridge them together). If it now works, the issue is normally corrosion of the C191 plug."

only problem is there is no pin 4 on my c101 its empty

any suggestions greatly appreciated!

[Brianmoooore]

That paragraph from the wiki looks very familiar!

Ever since the introduction of the 20 pin C101 to replace the earlier rectangular connector, pin 4 has been the home of the 'live' coolant temperature wire for the gauge, and it's always been a brown/purple wire.
Either you're mistaking which is pin 4, or whoever did the swap wasn't very good at electrics.
Has the gauge ever worked since the conversion?
Have you checked pin 4 on the body side of the C101?
Is there a brown/purple wire to any pin of the C101 on the engine side?