1999 F250 SD 7.3 diesel elctical prolems

When the key is off, some electical components stay on (radio, heater fan, cargo light) or come back on after the truck sets draining the batteries. Sometimes a pump can be heard pulsing under the hood when the key is off. Also the overdrive “OFF” light blinks on and off sometimes, when it does the cruise control does not work. The horn does not work but the horn relay clicks. I have replaced the ignition switch under the steering column, what’s next? How do I trouble shoot these problems and repair this vehicle?0

Let’s take a shot in the dark here. Open the hood and look at the break master cylinder. It has a sensor with is for the break pressure on the master cylinder itself, not the reservoir. If this sensor looks wet around where the plastic joins with the metal, disconnect the plug and go and buy a new sensor. This is the famous sensor that causes the Explorers to burn. Since there is 12VDC on this connector all the time, it may be shorting causing all of this.

I refer to this because both my truck and my wife’s Windstar did some strange things until I noticed the wet looking sensors. I replaced them and the problems just went away.

I think that if you check the owner manual you will find that the OD blinking, if functioning correctly, indicates that the transmission has a serious problem and should not be driven.