WTF, are you talking about !

He's referring to the rheostat dimmer for the instrument cluster and dash lights. Usually the left most knob on the cluster.

Early unit are simple rheostat potentiometer. Later versions (at least in 126) are PWM control units. They're backwards compatible too!

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Thats more clear, Thanks

Interesting, if they're PWM they should be able to dimmer a set of LEDs

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Not necessarily, they are likely too slow and you'd end up with a strobe instead of steady lighting. An LED responds to pulses a lot differently (faster) than an incandescent....

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I'm waiting for my soldering iron to heat up so I figured I'd give it ago:

From what the scope says, it looks like the PWM controller outputs about 160 Hz signal. Here's the datasheet on the IC: http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1408.pdf



I had some random 2V, 20mA Red LED sitting around, I threw a 500 Ohm resistor on it and here's the result. It does indeed dim... With better/brighter LED's you could probably achieve a better result.

For wiring reference:


Video, I didnt see any strobing effect when I filmed this:

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k