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Old 06-04-2000, 09:18 PM
David Radley
Posts: n/a
Gentlemen (and ladies!)

I have just taken possesion of my first MB (1990 500SL) so am new here. Please excuse any proceedural faux pas or breaches of etiquette.

I have two trivial questions to start with.

1) The light switch is not illuminated. I guess this is not right, and if so, how do I get to the bulb which I presume has blown?

2) On a closed throttle I can hear a gentle hissing noise, which sounds exactly like tape hiss from a speaker(and appears to be coming from the front right corner of the dashboard (right hand drive)). However, as soon as throttle is depressed, hissing vanishes. Any thoughts?

There are several more trivial points I need help with, but I guess I will feel my way in gently, not yet knowing if I am in the right place.


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Old 06-04-2000, 10:48 PM
Posts: n/a
Hi David,

Congrat on ur new motor! Do u mean the light switch for the instrument panel? It maybe just loose connection. I had it on my Infiniti and I correct it by just shaking the stearing column. Now I HAVE NO IDEA IF this WILL WORK ON UR SL SO U MIGHT WANT TO WAIT FOR OTHERS (MORE EXPERIENCED MEMBERS)' RESPONSES.

Regarding the hissing sound, it might be the sound from extra air intake. I notice on my 55 that once rev go past about 3000rpm there will be this "air sucking sound" if u listen carefully.

Just my $0.02,


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Old 06-04-2000, 10:56 PM
Registered User
Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
You have a vacuum leak in the back of the cluster, probably the economy gauge or a line going to the climate control. Are all of these items working properly?? The fact that it is evident with closed throttle (high manifold vacuum) and goes away with open throttle (decreased manifold vacuum) is a dead giveaway for vacuum problems. Check all of the above mentioned systems. Light switch bulb replacement usually requires removal of the fascia panel and the switch. Not sure on your car however..

Jeff L
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by jeffsr (edited 06-04-2000).]
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Old 06-05-2000, 08:40 AM
Mark Jeselnik
Posts: n/a
Hi David, I purchased a 1991 500SL about 2 years ago. Although, I have no insight for your current 'problems', we could 'talk' more about our SL's. My personal email is "". Look forward to hearing from you. Mark
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Old 06-05-2000, 08:56 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
The trim plastic will have to come off to replace the backlight for the light switch...

The hissing could be a vacuum line that has come off. I would have it checked at once, for it can alter fuel mixture.

Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
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