Disco 1 Discovery 300tdi electrics

Evening!

Recently got my first ever Land Rover (after always having a liking for them), picked up a very rough old 300tdi (one of the first 300tdi's i think, late 94). Mechanically it is "ok" (little issues, nothing too stand out, mostly just a couple of small oil leaks and a little sluggishness which is easy sorted) and body wise it is...well... like most of them, requiring a little welding but nothing too severe.

The main issue by a mile is the electrics. I guess you could say the important things all work, like the wipers, indicators, dipped beam, full beam, fan, fuel light etc but it has so many weird and wonderful "quirks" i'm not sure where to begin (perhaps earths aside).

The most amusing one is the sidelights. They both switch themselves on at random. If they haven't switched themselves on, you can switch them on manually at the stalk, and the stalk selects high and dipped no issue and switches them off, unless they switched themselves on, in which case they just stay on. Stalk seems ok as you can hear the relay clicking and it seems to control the functions fine and the dashboard illumination works when you select sidelights and dipped from the stalk, so seems the sidelights are just drawing power from elsewhere. Driving down the road yesterday afternoon and the headlight relay in the passenger footwell went mental, it was clicking away constantly like a sewing machine, i switched the headlights on dipped and immediately it stopped and returned to normal (i'm assuming again it's earth related). Today i changed the relay but the sidelights just decided again to turn themselves on, so seems it's not a relay issue.

I also have no kind of "warning" lights on the dash with the headlights (i.e a main beam warning), no kind of 4wd lamp illuminating when i select high or low diff lock or low range, oh and my handbrake warning light doesn't work (will flicker if you wiggle the leaver so assume just the switch faulty)... and one rear window doesn't work from the centre console controls but does from the door (again assume switch), but so many niggles hard to tell which ones are related!.

Any suggestions where to start looking?

Many thanks!

Get yourself a Haynes manual as that has easy to understand wiring diagrams for the early 300s then start testing each of the affected circuits.
There is no such thing as a 4wd lamp the only lamp to illuminate would be the central diff lock, with that either the switch or bulb could be faulty.
Haynes has all the info u need on that plus more.

Thanks, i meant diff lock light haha still getting used to the right names for everything. Will look into a haynes if i can't make progress, i'm used to sorting out Fiat issues so i'm sure i'll get there in the end haha.

Been doing a bit of reading up and i suspect (at least some of) my issues may be coming from the trailer socket as i found my rear drivers side tail light has "blown" as well. Read that's a possible sign along with random dash lights not working and the likes of the socket going haywire/shorting out internally and making the electrics do funny things. Will have a look in daylight at the fuses and clean out the socket and see what effect if any this has.

Problem still ongoing, but i've found pulling out fuse 15 (listed for air con and windows) fixes the random lights switching on glitch. I've lost my electric windows, interior fan and the interior lights, didn't think the lights were controlled by that fuse?

Am i probably right in thinking this points to the mfu being the issue?

All earths have been cleaned etc.

Windows work through their own controller in passenger footwell. I too have a dud switch but rarely have folks in the back so it can stay that way.

Mrcento said:

Problem still ongoing, but i've found pulling out fuse 15 (listed for air con and windows) fixes the random lights switching on glitch. I've lost my electric windows, interior fan and the interior lights, didn't think the lights were controlled by that fuse?

Am i probably right in thinking this points to the mfu being the issue?

All earths have been cleaned etc.

Click to expand...

Have you looked closely at the fuseboard ?

They can get gunked up, have loose bits and I've seen one that partially melted at the back shorting two different fuse points ...

Dippypud said:

Have you looked closely at the fuseboard ?

They can get gunked up, have loose bits and I've seen one that partially melted at the back shorting two different fuse points ...

Click to expand...

the fuse board looks clean, i've not had it out yet but all the contacts etc for the fuses i've had out have been checked and the back, from what i could see from a vid i shot to look at what mfu i had, all seemed ok, though you never know until it's out! that'll be the next job.

I tried pulling fuse 12, listed as the mfu fuse and it did nothing, the side lights and dash illumination still switched themselves on at random intervals and i still seemed to have full functionality of everything the mfu controlled!. I probably should have taken out 13, listed as ignition feed for mfu for a test but was running out of daylight.

The interior lights and boot light no longer working with the window fuse pulled is what's getting me though, they are meant to work on the clocks fuse as far as i know? seems like somehow they are what have been switching the sidelights on. It also seems my battery was draining silly fast when it did so, like in about 40 seconds when the engine was off and the lights had put themselves on, i think it seems more and more like something shorting out through other things.

I've done all the earths in both footwells, the 2 on the chassis rail and the one at the rear, cleaner out the trailer socket, tested all the relays at least i'm starting to track down parts of the problem!

just uploaded a handy image i sorted to print out while i was chasing gremlins round the disco hope it helps its the cab and under hood fuse boxes
https://s3.postimg.org/6e6bblfs3/Disco300_TDI_fuses.jpg

I think i'm getting closer to cracking the source of the issue.

I pulled a few fuses out and the only thing that stopped the lights coming on themselves was indeed fuse 15, the window/aircon fuse. So that's what's powering them on.

Another issue i have had has been my handbrake warning light. I pulled out the window switches to look into that and found that with fuse 15 in, when i was moving the window switch wires around, you could hear a relay clicking at the passenger side, wiggling around the window switch panel also caused it, so looks like there's a fault in there either with the wiring or one of the window plugs or switches causing a short of some description that's in turn powering the lights on (probably via the interior lighting circuit and through the stalk).

good detective work that man, be interesting to see what the culprit is.