Dash Dimmer Repair

Ever since i have had the car the dash lights dimmer has never really worked – it’s either on or off……nothing in between. I have a replacement that i got from an auto-jumble which was sold as NOS (new old stock) so was ready to swop.

First i disconnected the battery to avoid any sparks whilst fiddling behind the dash. The tacho needed to be removed – not taken out completely but can be left connected to the wiring. Quite a straight forward job just a matter of feeling around gently around the back of the tacho for the little round knurled nuts to release the clamps. Once removed the tacho can be eased out.

Then it is quite easy to get to the back of the rheostat (dimmer switch) which is just a variable resistor that over time simply wears out. The knob is removed by pushing in a small stud on the side of the knob and then release the chrome nut the holds the dimmer on the dash. Once released it can be extracted through the tacho hole. I could see straight away that someone else has obviously had a go at this in the past based on all the tape wrapped around it to hold it together. I swopped the wires on to the new switch and put the power back on to test it.

This is when i realised that the bargain i got from the auto-jumble was a load of crap!! It again just on-off!!

I decided i would take them both apart to see if i could make one good one. The – so called – new one was full of bits and the circuit lines badly corroded the one i had just taken out seemed tho have a piece of the circuit missing which obviously would cause a break the circuit. I soldered a small wire across the gap to re make the circuit. Tested it and “hey presto” it worked the dash lights dimmed.

Tried to work out how the thing worked following how the flow would find it’s way through the points and around all the little “printed” circuits…….but beyond me.

I drilled out the old rivets that holds the case together but could not find any suitable screws so like the PO used some tape to hold it together!! but with a small cable tie as well for good measure. Refitted it and the tacho (make sure you put the earth wire back behind one of the knurled nuts on the back of the tacho)……..and job done.

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