Hi
Here’s a composite image taken from the [https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi7nsT0wMLzAhVBJHIKHWmyCGcQFnoECAMQAQ&url=https%3A%2F%2Fwww.vintageshifi.com%2Frepertoire-pdf%2Fpdf%2Ftelecharge.php%3Fpdf%3DKenwood-ELEVEN-Service-Manual.pdf&usg=AOvVaw3kX-x91FPWwF9GqcjLTWFj|service manual] showing the dimmer switch circuit.
Looking at the circuit the switch at normal bypasses the [https://www.ebay.com.au/itm/122168160827|1Ω 7W resistor] in the power supply path to the lamps (see red arrow line) and when operated inserts the resistor into the circuit (see green dotted line).
[image|2494463]
(click on image to enlarge)
Unfortunately the parts list doesn’t have the switch part number only the board number (X13-2190-10) where the switch is located.
If the switch is faulty and not say the resistor etc then search for a suitable DPDT switch (double pole, double throw). The voltage supply for the lamps is only 7.5V DC and the power rating for the resistor (7W) indicates that the current is about 1A. Search for a switch that has these specifications as a minimum e.g. 2A DPDT locking switch.