whats wrong with my tach

[91ford7.3td1in]

when i turn on my lights or my heater my tach drops to 0 i have a 91 f250

 

[1Turbo10]

I have the same problem! Hope someone will post an answer. I am guessing a ground problem.

 

[91ford7.3td1in]

i now its frustrating me that i dont know how to fix it

 

[Shadetreemechanic]

Most likely your tach sensor is either bad or dirty. It is located on the timing gear cover on the front of the motor. You can try unscrewing it and cleaning any oil or gunk off the pickup. That will probably do it, but if not you can replace it.

 

[tractorman86]

the wires comming out of it are probably dry breaking mine did that so i pulled the harness around the front of the oil fill.