what would cause the Speed O to not work after having front end breaks replaced?

@Tom, they checked under the car an couldn't find anything wrong. Not sayin much about SEARS AUTO but still the head mechanic is a fellow Merc driver.

The Speed Sensor broke internally, the Speedometer cable broke or the Speedometer head failed. Like Tom said - it worked when you brought it in.

@Tracy Yes that was said. Unfortunitly Sears Auto service centers are no longer geared toward whole car repair. (Thanks KMART). Was told to take it up the road an have a computer hooked to car. Am like hello this is a 20 year old car an no one not even FORD dealership have the correct plug in's anymore let alone a person who reads PRE-DOS programing. Just gona go an get a new unit from a junk yard an deal with it like I have in the past.

Well, a little research (and I mean a little) will tell someone how to use a volt meter to read codes from your EEC-IV system but that's not the problem. I don't know about where you're from but in CA, we have the Bureau of Automotive Repair. They oversee the practices of shops in California and get people's cars fixed. Ok - enough preaching - I'd start with the simple stuff: Pull the Speed Sensor out of the Output Shaft Housing of the Transmission and give it a spin. That's the most common failure. Check all of the fuses too. I just did a little research to find that your Speedo is electronic. If you have a volt meter, set it to AC at it's lowest setting, hook up the leads and spin the sensor - there should be a little voltage. Hope this helpd - Tracy

BTW - I still have an EEC-IV tester. Most of the new Professional scanners can check for codes too. They just don't want to work at it - it's much easier to see what a system or component is doing via network than it is to actually do some diagnostic work with a volt meter and actual talent. (There I go on my Soap-box again)

Ah not on a system that was rewired by squirrels an possoms. lol Auto zone plugged in an got a failure to read light on there diagnostic handheld as did Local Ford dealer with there big computer on a cart machine. An just on a side note all Crown vics an Mercs an town cars sold in the US from 92 to 2011 were designed in USA but built an shipped primarly from CANADA for the Eastern an Northern US.

@Tracy. checked the fuse box as of now not only is the Speedo out but so is the miles an trip guages. Fuses check out. So am looking at full replacement of gauges.

Scary - critters do a lot of damage. For a minute I thought you were going to say something about Bailing Wire and Chewin' Gum! :)~ I've been a Ford Tech since 1987. I've been around them and worked on them all of my life. Currently, I work on a Fleet of over 800 Crown Victorias (same car - a little different logo - ballistic shielding in the doors.) I won't say that I know it all but I'm glad to help if I can.