Mark VII Speedometer

Buzzy4542

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I have a 1989 Mark VII with 63,000 original miles. The car sits for 9 months in a garage with a dehumidifier running. I now find that the speedometer shows "0" for about the first 10 minutes of driving. Then it comes on and works and the odometer also starts working. During this "warm up" period, the gas gage jumps up and down (a gallon or two) but in the range of what is actually in the tank. When the speedometer starts working, the gas gage works perfectly. Any ideas what is wrong or what needs to be fixed? Any and all suggestions welcome. Thank you. :L :feedback
 

Joeychgo

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IM wondering if its electronic - but im not an expert on the Mark VII
 

OldSchool1

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If he's reading gallons then it's the electronic dash found in the base model 1984 or any Bill Blass from 1984 - 1992.

1989 was the last year for the "dashboard grounding problem". Do a search for GROUND WIRE DASHBOARD MARK VII (google quoted me from another board) and you'll see the fix. As soon as I can I'll write a (lo)tech article on this repair.
 

JPJP

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Buzzy4542 said:
I have a 1989 Mark VII with 63,000 original miles. The car sits for 9 months in a garage with a dehumidifier running. I now find that the speedometer shows "0" for about the first 10 minutes of driving. Then it comes on and works and the odometer also starts working. During this "warm up" period, the gas gage jumps up and down (a gallon or two) but in the range of what is actually in the tank. When the speedometer starts working, the gas gage works perfectly. Any ideas what is wrong or what needs to be fixed? Any and all suggestions welcome. Thank you. :L :feedback

I had similar problems only the gas gauge stopped working some time ago. The tach also didn't work properly when I turned on the lights. I fixed the ground problem (orange wire dash ground procedure shown on this site) and have perfect working conditions for the tachometer and gas gauge only the speedometer still didn't work till I had driven the car about 10 miles. I went ahead and got a vehicle speed sensor from a local parts store (Murrays) for $22.99 plus tax. The speedometer works fine now. Only one screw holds it in place at the tail housing of the transmission. This is something to try if the ground is not your issue.
 

WALT

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Before you spend a lot of money changing parts --
Pull the Instrument cluster and clean the connector terminals
with an eraser as they are very corrosion prone -- the cluster has a
printed circuit contact strip
and the connector has metal tabs -- make sure the metal tab is not
jammed in the connector -- it should have a little spring action
when pressed down -- Pulling the cluster can be a bit of a pain
but just take your time and be caerful prying the trim pieces out
( most of the pieces are held in with tension clips ) and do believe you have
to lower the steering column too -- sounds bad but its really not too hard -
Good luck
 

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