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#1
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tachometer fluctuates wildly when radio volume turned up
Hi Mercedes dudes,
I need som help with this one: Recently my tachometer has started to fluctuate wildly, with the engine RPMs rock steady. So it it is clearly an electrical problem. I have noticed that it is clearly correlated to the volume of the radio. If i turn the volume all down, it is fairly steady. As sooon as the volume is turned up and reaches a certain threshold, the tach starts to bounce up and down. I replaced the OVP with a another, just to rule that one out. It didn't make any difference. Another problem with an intermittent ASD light turning on made me suspicious about the OVP. The voltage over the battery terminals during idle and with the radio turned up is varying in the range 14-15 V. My assumption is that it is must be related to the draw of amps that increases when the radio volume is turned up and somehow starves the tach, but the battery voltage as mentioned, doesn't drop significantly. Do any of you have any suggestions? The car is a W124, 300E 12V, 1990. Thanks BR Viggo |
#2
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Answer
My best guess:
* The radio ground or power are connected to the wrong circuit. * The radio ground is not connected or damaged = back feeding ground through any available circuit. .
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ASE Master Mechanic asemastermechanic@juno.com Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 1984 190D 2003 Volvo V70 2002 Honda Civic https://www.boldegoist.com/ |
#3
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On my '83 CD, the tach dances a jig when I honk the horn, , , yes, I use it quite a bit.
-corne- |
#4
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Viggo, does it have the original radio?
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Click here to see the items I have up for auction at EBay Click here to see a photo album of my '62 Sprite Project Moneypit (Now Sold) |
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