For the past two weeks I have been chasing down a speedo promblem. So here is what has happened. About two weeks ago we go a little snow here and it was pretty cold so I went to leave in the morning and I turn the key and look for the wait to start light. But it wasn't there. So I turned the key off and back on and start it up anyways. A few cranks and it here we go. The problem is that it idled real rough and shoke real bad. When it got warmed up and I left no Speedo!

So I have replaced the speed sensor on trans and replaced the dash pod.

It never occured to me that the two were related until last night when I remebered (maybe incorrectly) that the grid heater shuts off when the truck reached a certain speed, so I am thinking that this may be my promblem only

I don't know what this piece is so that is my main question.

And is there anything else that could be wrong? All of the cables and connections appear to be in good shape.

Sorry for the long post,
TIA

 

Have you checked your fuses?

 

All fuses are good.

 

My speedo nor grid heaters worked, I just wired my heaters to a switch not thinking the two were related, but if a speed sensor isn't the problem then I would really hate to spend $70 and it be something else and my speedo STILL not work, keep us updated!!


Chris

 

I don't believe the grids turn off at a certain speed. They turn off when a certain air charge temp/coolant temp is reached...I think. Someone will no doubt correct me if I'm wrong. To me...it sounds like you didn't have grids at all BEFORE the snow. They probably quit working when the speedo quit working. Sounds like some power feed is not getting it's power. Could be a fusible link. They're on the driver's fender and a pain to check out. I wiring diagram could be useful here. See if there's common feed to the speedo and the grid relays. Maybe the iginition switch? Not unheard of for that to go bad. Anything else electrical not working? Maybe another clue hidden somewhere.

 

The Grid heaters and speedo worked fine the night before and I think I have checked all of the wires.

But if someone has a wiring diagram or knows where to get one it would be appreciated.

 

I believe both are powered off the auto shut down relay but not sure since don't have FSM in front of me. Might start checking to see if the relay is good.

 

The only input the computer/grid controller uses to determine when to run the grid heaters is the intake air temp when the key is first turned "on". It doesn't even care what the air temp is after you start the truck, only that first key-on reading. No speed cutoff on a 1st gen either. The grids will run for whatever time the computer/grid controller selected even if you are doing 75 mph.

You have a power problem somewhere. Ignition switch, fusible link, fuse. It really sounds like you blew fuse #12.

 

Thanks for the replies guys but I look under the hood and see a whole tangle of wires and stuff that isn't plugged in and where nowhere to plug it in to.

Where can I get a wiring diagram for my truck?
I believe with one of those and some time I can figure it out.

 

Oh I checked the rest of my electrical functions and they all work. (wipers, blinkers, etc..)

 

Bump.
I have searched for a wiring diagram but no luck. anyone?

 

If you would fill out your signature so we know what truck you have somebody probably has a copy of the wiring diagram. I have the 93 FSM.

 

My signature only displays in the first post. When we they went to the new software it changed that.

Its is a 91' 250 2wd five speed