Hey guys. My speedo/Odo is dead, hard shifts, OD light flashes, code 542 fault etc. I checked continuity on fuse 8 and 18 in the cab and they're fine. I checked to see if i had voltage at both fuses and there is nothing coming to fuse 18. No continuity/resistance to ground from either side either so it doesnt appear as though anything is shorted out.

Anyways, does anybody have a schematic for that fuse panel (or the VSS circuit) handy? I looked all over and cant find much past what fuse does what... I'm pretty sure its just a loose wire. I havent had the truck all to long, but it worked week or two ago then it didnt, then it did...then it went out again lol

I found this off another post but i really cant make out what it says
http://img36.exs.cx/img36/6751/1992upfusebox27yh.jpg



Thanks in advance

 

Check fuse labeled "S" in the engine fuse box (50amp maxi), it supplies power to fuse 8,4 and 16 in the cab. If that's good, check for open connectors or bad wires.

Also check your dome light, it can short out(melted plastic) causing all the above problems! Blowing fuse 8 causing the PSOM(speedo) not to send speed info to the ECU, causing the tranny to hard shift and OD light to blink.


Fuse 18 comes off the ignition switch and is hot only in "run". Fuse 15 also is tied to that same circuit, so if fuse 15 has power and 18 don't then there's a bad connection behind the fuse box or ignition switch splice.

 

the VSS has went bad.. common issue.. easy to replace..

 

Thanks. I'll have a look when i get home today. The interior dome light and fuse 8 are working fine. I saw that somewhere on another thread though...lol Is there a relay in line with those circuits?

(edit) never mind the relay question. just saw the rest of your post. need coffee...

 

Bad VSS wouldnt explain a dead Odo or lack of 12V to fuse box on F18. That would lead me to believe there's a short..

 

VSS/PSOM Diagram from Steve83


Snagged from here: 1983 Ford Bronco PSOM picture | SuperMotors.net

 

X2

 

i dont like to just replace parts without a proper diagnosis

that site is a freaking gold mine haha that combined with this should net some results





Figures, i search for two days for that diagram to find it just after making a thread for it. fail. LOL

anyways, i'll do some readings tonight and post my results. I'm guessing either a faulty ign switch or PSOM.

thanks again!

 

Turned out to be the instrument cluster after all.Hurray for proper diagnosis and not dumping money into random parts. She's up and going now. Fyi

 

Glad to see you got it figured out!