P38A Umm help P38 electrics have gone mad. won't lock, lights on/off wipers etc

As said the p38 has gone mad this morning. Came out. Unlocked and starts fine but the electrics have gone mental.
Lights are on, off, on ,off, on ,off. Doesn't matter if switch is on or off. Wipers seem to have intermittent power on max only and stop halfway across the screen, central locking has stopped working although truck starts fine and isn't laboured either. Flashed alternator fault for about half a second so will check I've got a decent output later. Dash doesn't beep at me to tell me the fuses (which I don't have as BECM has been swapped at some point) have failed. Radio is fine and indicator aren't working properly either ??? WTF is going on???

Low battery volts most likely.

Fully charge battery with battery charger & take it from there.

Be nice if it was. I’ll check it later and put it on charge. Interestingly enough I did about 300miles in it on sunday which is very rare. So if anything if should be well charged. I’ll check it once I’m home.

Check battery connections & any earth straps.
Worth trying a jump lead from battery earth terminal direct to a good clean point on the block & see if it makes any difference.

12.5 v so half charged battery. 13.7 v back when to battery when running. I also noticed the osr door is locked and won’t unlock. All the rest are unlocked. I opened this this morning just before the problems started. Interior lights don’t work and nor do windows. Climate seems fine

So reading up there are a couple of extra things to check but anything missed will be appreciated. So to do over the next day or so.

Battery off for a good overnight charge first of all.
Clean terminals and battery posts too.
Check voltage drops across battery leads. Are there any specific cables to check voltage drops across other than the obvious ones? for example the ones to the BECM?
Pull the fuse box and have a check and see if it's looking burnt at all.
Check for water ingress under the kick panel although I've checked before and it's always been bone dry.

With BECM failure now rolling round in my head some other options to look at would be nice.

Joss155 said:

Check voltage drops across battery leads. Are there any specific cables to check voltage drops across other than the obvious ones? for example the ones to the BECM?

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There's an electrical troubleshooting guide on RR.net.

Check if under the carpet in the drivers footwell is wet.

So come on then. Who would like some winning lotto numbers????

Disconnected battery. Cleaned terminals
Cleaned alternator wires.
Checked fuse box (looks brand new)
Thought meh lets just put power back to it.

It’s like nothing has happened. Everything came back. Lights,CL, windows. Just the osf window won’t set?

I’ve left it on charge.

Joss155 said:

So come on then. Who would like some winning lotto numbers????

Disconnected battery. Cleaned terminals
Cleaned alternator wires.
Checked fuse box (looks brand new)
Thought meh lets just put power back to it.

It’s like nothing has happened. Everything came back. Lights,CL, windows. Just the osf window won’t set?

I’ve left it on charge.

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Still check for wet under the carpet. 13.7 volts from the alternator is not enough, should be 14.5 to 14.7 volts.

Checked mate. Dry. Defo time for an alternator though.

Joss155 said:

Checked mate. Dry. Defo time for an alternator though.

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Is yours original spec? 13.8V set point on the diesel. It will kill calcium batteries over time as not high enough. A bad battery can pull the volts down too.

Yes mate I would assume so as I've never touched it. The alternator mod has been on my list for a while now you've jogged my memory

Grrrrrr said:

Is yours original spec? 13.8V set point on the diesel. It will kill calcium batteries over time as not high enough. A bad battery can pull the volts down too.

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13.8 volts pre 99.

Hi, This might seem silly, but i had this on my P38 and it turned out to be water in the indicator unit, replaced the unit and it all went back to normal.

Mine did that.... I dont know why!!

Well all seems fine. Even the window set has come back.