Voltage spikes and relays

martinkuetzing at att.net martinkuetzing at att.net
Thu Feb 28 09:59:31 PST 2008

Scott -

As with the other comments about your post, more info is needed to help you narrow things down.

I found two issues that may be of help to you.  First, the filter capacitor was missing from my alternator.  Adding that quieted down most of the noise on AM reception.  This condition was easy to test once I realized that I could have the radio on with the engine off.  Before the cap was installed the noise would go away only with the engine off.  It took a bit of thinking about it though, to decide what that observation meant.

Similarly, there was a need for a cap across the main cabinet blower motor.  Here again, the noise (mostly with AM reception) went away when the climate control was turned off.

But, if you figure this out for your own car, let the rest of us know what you did.


-------------- Original message from Scott Elliot Gilman <scottegilman at mac.com>: -------------- 

> My '91 200 TQ has developed intermittent electrical spikes, which 
> causes problems with the audio system. The radio and speakers were 
> checked out, and they are not causing the problem. The audio tech 
> believes the problem may be a result of a faulty relay. Where can I 
> find a schematic diagram showing the relays? How many relays are 
> there on this model? Also, what do the relays cost? I've heard that 
> they may be about $60 each. I suspect they're more. I don't know 
> much about the car's electrical system; fortunately I've got Becker 
> Audio in Hatboro, (north of Philadelphia) doing the work. Becker's 
> rates are fair and the shop has an excellent reputation. Thanks 
> for the help. 
> Scott 
> 1-owner '91 200TQ with 107K 
> NYC 
> _______________________________________________ 
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