Hi, I've been searching (honest) and can't quite find the answer.

I picked up a bunky el auto and most of the time the box is stuck in first.

Sometimes it will go into other gears when you select them but has no kickdown and if left in drive will run only in third gear (limp mode?)

The speedo doesn't work.

I've been told it's either the gear selector switch, speedo sender unit or low fluid level. I haven't tried starting in gear. Reverse is perfect and when it's working in manual mode the gears select fine with no slip etc.

Ideas? Oh, and how do we read the faultcodes?

if it's in limp mode, i'd be checking the thermo fan relays, the wiring loom from the engine bay to the gearbox, the wiring loom INSIDE the gearbox, and the Nutreal saftey switch. Other than that, i'd be checking fluid level, and beyond that, I reckon it's an S5 solenoid fault.

EDIT: I just read the speedo doesnt work, which also makes me think it's the loom from the engine bay to the gearbox, fix that first

Gab

if the loom is fine, check if the inhibitor on the box is ok.
it tells the ECU which gear position is being used by sending a certain voltage signal.

but cleaning all the connectors on the loom is a good place to start.
the S5 solenoid only controls line pressure, not gear selection, S1 and S2 control gear selection when told by the ECU.
by default, limp mode is no signal sent to either S1 or S2 to enable you to drive the car without power to the box.

Replace the speedo sender and see how it goes, once you get your speedo working, then you will find the trans issues most likely resolved, as the ecu requires a speed signal to schedule the gear shifts, without it it will resort to LHM which is 3rd gear

Thanks for the replies. I've got a spare speed sender and gear switch so will swap them over and report back...

and the winner is....... 66 coupe.

I made a little fault code reader, which showed a speedo sensor fault. Replaced the sensor and it's all fixed.

I am having almost the exact same problem. Usually only once the car reaches operating temperature. The speedo then drops to Zero, box in LHM with me still being able to select 1,2,3 by shifting at will. This problem thereafter will cut in and out. Sometimes seems to fix itself and can be driven for a further hour or more without seeing the prob again. Turn car off, turn it back on again before it cools completely and I am likely to have the prob again within minutes.

I don't want to source a speed sensor if its more likely to be a solenoid. Also I have read on various threads here that the wiring can be a cause, even as far as some suggesting cleaning battery terminals?

How do I make one of these "fault code readers"? Or even how do I get the fault codes from the car (bridging contacts, counting flashing warning lights ???) for an EA?

That is most definately your problem, most likely the sender, at worst, the cluster.
Senders from the wreckers / someone wrecking a car shouldnt be too expensive, start there...

Make up a fault code reader- instructions are somewhere on here with a link to another site. Then you can see what the computer reckons...Sorry can't give you the link as it's on my knackered laptop. I'll see if I can dig it up later on. Try a search for falcon fault code reader or similar and have a good look.