I'm having problems with my '90 129 500SL Euro. Before startup, key position 2, the ABS and ASR lights in the speedo area do not light. The ADS switch does not light, this is the one on the centre dash board for firmness, not the one on the outer dashboard for ride height which is lighting. The ride height appears to be working except on the right rear wheel where there is no movement. Also with ride height up I can here a faint hissing noise from the rear which stops when I drop the car. I have been hearing an electronic clicking sound from under the car but this has stopped. Hydraulic oil level is correct. Also car is fitted with non-original brake pads with no sensors which may explain ABS light not coming on. Any help please?

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'66 W100 600 SWB
'05 W463 G55K AMG
'91 W126 500SEL
'93 W463 300GDL
'84 W460 280GES
'83 W460 300GDL
'66 W111 220SEb Coupe
'58 W121 190
'58 W180 220S
Have previously owned '99 SL600, '99 ML320, '79 450SLC, '79 450SEL 6.9 x 2, '68 600, '91 190E 1.8, '90 190E 2.0, '85 190, '90 500SL, '92 500SEL, '97 E300Turbodiesel, '91 300D, '72 280S, '82 300D, '81 300SD, '85 230E, '56 220a and I'm sure I'm forgetting some.