My 07 F350 has a 6.0L and it has 85k miles on it and just last week the speedo and the tach are actin all weird. the speedomator will give itself a new 0 each time i stop. Like im goin 60 and stop at a light now it shows 35 then i go again and it adds my speed to that till i stop the it might be 70. And the tachomator will be off by typicly 1k rpms. only way to reset is by un hooking the wire off the driver side battry. Ford has no clue and it sucks to be you..... Iv checked all the harnesses under the hood and they all look ok and ideas?

 

A) Verify batteries in good shape by charging then load testing individually.

B) verify cables good, connection good.

C) verify alternator output good

D) disconnect batteries, reset computers.

 

My 06' F-350 did that one day,,,the Next day it went back to Normal and has not happened since !!,,, But I do recall hearing around this year the did sometimes have a Gauge Cluster Go Bad !,,,Good Luck.

 

2 new bateries less than 6 months old altanator tests good but has like a soot around the top of it. cables all look good as far as i can see. i have the dash apart now looking at the wires but which ones r for the speed and tach?