intermittent loss of lots of dashboard electrics

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ndh
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intermittent loss of lots of dashboard electrics

Post by ndh » Sun Jul 28, 2019 1:52 am

The other day rather a lot of electrics failed at the same time (voltage gauge, fuel gauge, temp gauge (but not oil pressure gauge), indicators (but not hazards), tacho and overdrive switch) with gauges at far left zero position. After a short interval and all of a sudden they all sprang back to life at the same time and worked for a few days but have now all failed again. My blind guess is that this might be an earthing fault. Is there an earthing wire that would apply to all of these which should be checked and cleaned up? Of some other single point of failure which would affect all of these things but apparently nothing else (well, it could affect other things but nothing else i have notoced / found yet)?

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intermittent loss of lots of dashboard electrics

Post by philhoward » Sun Jul 28, 2019 5:57 am

Usual suspect is the “Ignition Control” fuse - or indeed the fuseholder itself. If a 6-series it could also be the ignition relay but the fuse would be the first on the list.


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intermittent loss of lots of dashboard electrics

Post by scimjim » Sun Jul 28, 2019 9:49 am

Wiring diagram here Nick. To confirm it’s the igniition control fuse, check your reverse lights. If it fails again, note that it supplies the radiator fan, so don’t get caught in traffic :D


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intermittent loss of lots of dashboard electrics

Post by ndh » Sun Jul 28, 2019 2:12 pm

Thanks, will have a look.



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intermittent loss of lots of dashboard electrics

Post by Oldconn » Sun Jul 28, 2019 3:06 pm

You might also search behind the instrument panel which includes the rev-counter and the speedometer. Under there are several multi-pin plugs which link sections of the wiring harness. If these have ever ben wet (leaking windscreen seal for example) , they are likely to be oxidised and making intermittent contact-- don't ask me how I know! Pull them apart and inspect the pîns , try a cleaning spray, or replace with new plugs.


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intermittent loss of lots of dashboard electrics

Post by ndh » Sun Sep 08, 2019 9:12 pm

this worked ofr a whlile so i was less bothered but has started playing up again. It does not seem to be the fuse, it did not look blown but has been replaced anyway. It may be some kind of loose connectionin the fuse holder as taking the fuse out to check and putting the same fuse back has on occasions brought everything back to life so i suppose i should look at that (although am not overly keen as the last time i did anything like that - on a Rover P6 - i got no end of grief from a load of v short and fiddly wires and and backache from general contorsionism).

Philhoward mentioned the ignition relay. where is it - if it is easily accessible i would be tempted to replace it first anyway to rule it out.



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intermittent loss of lots of dashboard electrics

Post by Roger Pennington » Sun Sep 08, 2019 9:46 pm

ndh wrote:
Sun Sep 08, 2019 9:12 pm
Philhoward mentioned the ignition relay. where is it - if it is easily accessible i would be tempted to replace it first anyway to rule it out.
It's one of the three relays that you'll see in front of you if you take out the lining of the glove box (two screws - one each side). You could either find which one it is by comparing the wiring colours with the diagram, or by a process of elimination - the other two are the auxiliary lights and the outer main beams, so you could pull them out in turn, and see what doesn't work.


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intermittent loss of lots of dashboard electrics

Post by scimjim » Sun Sep 08, 2019 9:47 pm

Sounds like the fuse holder “ears” to me. Also check the rear of the fuse holder isn’t melted. No point in randomly replacing stuff in the hope that it cures the fault.


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intermittent loss of lots of dashboard electrics

Post by ndh » Tue May 19, 2020 12:19 pm

this has continued as an intermittent fault for ages without ever being completely reliably resolved but is now more of less permanent.

I am satisfied the fuse box isn't the problem. I have also checked the ignition switch itself and checked the multi pin connector beneath the steering column. Only thing that got life out of it was when i located the ignition relay, cleaned it up and put it back but sadly my moment of supposed triumph was short-lived.

I now propose to replace the ignition relay but rather foolishly put it back before taking a photo of it / noting down the details and cant find anyone selling the self same lucas part (it is round). Presumably these are fairly generic - could anyone please tell me what i could use to replace it?

Thanks



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intermittent loss of lots of dashboard electrics

Post by Oldconn » Tue May 19, 2020 5:54 pm

Mine isn't round, its a bog-standard square relay rated at 20 amps, which sounds a bit marginal, but its never caused any problems.


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intermittent loss of lots of dashboard electrics

Post by Oldconn » Tue May 19, 2020 5:59 pm

I still favour your first instinct, ie: faulty earthing. The metal bar which runs laterally behind the dashboard is connected to metal uprights next to the A pillars, and these should all be connected to the chassis. To inspect thoroughly you need to remove dashboard panels and footwell side panels.


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intermittent loss of lots of dashboard electrics

Post by ndh » Thu May 21, 2020 11:24 am

Oldconn wrote:
Tue May 19, 2020 5:54 pm
Mine isn't round, its a bog-standard square relay rated at 20 amps, which sounds a bit marginal, but its never caused any problems.
as it happens i had a standard square relay rated at 30amp and put that on. same old story, it works briefly then nothing (in which case it is possible that that the original ignition relay may not have anything wrong with it).

Presumably the metal bar acts as the earth for lots of things? if so and that isn't earthed wouldn't other things also fail?



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intermittent loss of lots of dashboard electrics

Post by scimjim » Thu May 21, 2020 11:44 am

Start from basics. Confirm everything you have lost and everything you still have (using the wiring diagram, so interior lights, reverse lights, etc,etc,etc) to confirm it’s the relay or not. If replacing the relay doesn’t fix it, it’s one of the wires to the relay.


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SECURE DRY STORAGE FOR YOUR SCIMITAR

Current: SE5 (8Ball), TI SS1 (snotty), 1600 SS1 (G97), 1600 SS1 (C686CCR), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), 1300 SS1 (Number One) & Sarah's coupe.
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intermittent loss of lots of dashboard electrics

Post by ndh » Fri May 29, 2020 7:39 pm

the dashboard electrics now seem to work when it first starts up and i drive off with all seeming well however the moment i try to use an indicator the electrics go off and will not come back on.
Oldconn wrote:
Tue May 19, 2020 5:59 pm
I still favour your first instinct, ie: faulty earthing. The metal bar which runs laterally behind the dashboard is connected to metal uprights next to the A pillars, and these should all be connected to the chassis. To inspect thoroughly you need to remove dashboard panels and footwell side panels.
I have tested the earth on this bar with a circuittester and it seems fine



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intermittent loss of lots of dashboard electrics

Post by ndh » Fri May 29, 2020 8:08 pm

scimjim wrote:
Thu May 21, 2020 11:44 am
Start from basics. Confirm everything you have lost and everything you still have (using the wiring diagram, so interior lights, reverse lights, etc,etc,etc) to confirm it’s the relay or not. If replacing the relay doesn’t fix it, it’s one of the wires to the relay.
ok will start trying to work through it.

if i understand the wiring diagram correctly
-the electric windows heater fan and indicators run off the relay (ie the pink and white wire off the relay and its various offshoots) and
-the other ignition controlled stuff is not controlled by the relay but simply by the ignition switch (ie the white wire from the switch and everything that branches off it, one of which is to the ignition relay

???



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