Lotus Elan

INdicator earthing problem?!?

PostPost by: ianf » Sun Oct 04, 2009 5:53 pm

Evening all,

I have a frustrating electrical problem (surprise surprise)! I have just returned from the Spa 6 hours which was great, however while in convoy with friends they reported that my brake lights and rear lights were flashing in time to the indicators at the rear. I also find that the reversing lights are doing the same.

Easy - clean up/add earths to the rear light units and problem solved - er no. Putting jump leads on the rear units and connecting to the battery has no or little efect and I have checked the earth of the flasher unit. So the indicators appear to be earthing partly through the other lights. NB one rear light unit earth comes from the indicator the other side from the stop/tail light.

To help with diagnosis (if not bleeding obvious) the tacho occasionally died while on the trip (& the heater valve leaked when the heater was off and the speedo odo and trip gave up as well!)

So a bit stumped and as the Elan is my only car (apart from The Managements MX5) at the moment it would be good to fix.

Any suggestions greatly appreciated.

Many thanks,

Ian
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PostPost by: paddy » Sun Oct 04, 2009 6:13 pm

It does sound like a classic earthing problem, but it's v odd it makes no difference to earth the units directly. I would disconnect all of the units (or remove bulbs) for every light except the one you're trying to get working and directly measure the resistance from the -ve (ie earth) side of the lamp to the battery -ve.

If you really end up tearing your hair out then you're welcome to bring it round and I could have a look (and/or give moral support).

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PostPost by: ianf » Sun Oct 04, 2009 6:25 pm

Hi Paddy,

All the lights are working - they just all want to work together! I will bear in mind your offar I'm 3.5 miles from Wokig station!

Cheers,

Ian
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PostPost by: 69S4 » Mon Oct 05, 2009 7:16 am

Hi Ian. I spent weeks chasing down exactly this sort of thing earlier in the year, giving up and walking away on several occasions :? :? . You may find that the poor connections (not always earth connections) are at the other end of the car, under the dash, anywhere other than where you thought they should be.

Paddy's suggestion of isolating systems, getting them working and then adding back the common wires to another system is really the only approach unless you strike lucky and find it's all down to one bad connection early on. In my case it was multiple bad connections and I must have re made just about every earth on the car and re soldered about 30 bullet connectors. I made up a couple of long cables, with one end bolted to the cam cover and the other ends fitted with small crocodile clips to act as my instant test earths. I would then disconnect all of the earths for a system, check it worked with my flying earth leads and put everything back one wire at a time. On many occasions just taking the connections apart and putting them back together again would fix the problem.

Most of the poor connections were at the front of the car, in the nose area and you've got common connections here for indicators, side and headlights that would cause your symptoms. Worth checking in this area as well as at the rear. I got to be very familiar with the circuit diagram.

Not the easiest of things to concentrate on if you need the car for everyday transport.


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PostPost by: ianf » Mon Oct 05, 2009 6:44 pm

Hi Stuart,

Thanks for this. The reason I checked the flasher unit was that I was wondering if the problem could be at the other end of the car. I had an iffy front flasher earth last year so will have a look at that end tonight. Did your front sidelight flash as well? I don't have to use the car every day but don't really want it off the road at weekends. I can drive it but when braking everything becomes a bit silly.

Thanks again.

Ian
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PostPost by: RotoFlexible » Mon Oct 05, 2009 8:14 pm

Ian,

I've had problems over the years with a loose fit between the lamp sockets and the plate into which they are inserted. If the socket is loose and/or there is a bit of corrosion on the socket or the hole in the plate, you can get the symptoms you've described. Also, check the fuse box; I've had odd symptoms produced by loose or corroded fuses.
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PostPost by: ianf » Mon Oct 05, 2009 8:38 pm

Thanks all,

I have cleaned up all the rear earths and connections and the bulb holders (the resistance is pretty even now) and seem to be about 75% there. Cleaning the inside of the rear lenses brightens the lights by about 20% as well!

Going to carry on cleaning stuff under the dash (brake light switch etc) and hopefully it will improve some more - I reckon it would pass an MOT now unless it was carried out at night. I will try with the engine running and generator charging as maybe a lack of volts could be contributing to the last bit?? Then I will do the fuse box, front end etc - at least its driveable now.

I will let you know how I get on in a few days.

Cheers,

Ian
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PostPost by: paddy » Mon Oct 05, 2009 10:10 pm

ianf wrote:I will try with the engine running and generator charging as maybe a lack of volts could be contributing to the last bit??


It's not the voltage, but the relative resistance of the earth return path versus the return path made by going around the other lamps to their earth. (If anything, more voltage will make everything brighter, including the wrong lamps.) Since a 25W bulb is ony 6 ohms, you will get these symptoms even if there is only 2-3 ohms resistance in the earth, which is hardly anything at all. All of the earths really need to be pretty much perfect to get the resistance down to a sufficiently low level that you don't see these symptoms.

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PostPost by: 69S4 » Tue Oct 06, 2009 6:53 am

ianf wrote:The reason I checked the flasher unit was that I was wondering if the problem could be at the other end of the car. I had an iffy front flasher earth last year so will have a look at that end tonight. Did your front sidelight flash as well?
Ian


That was one of the symptoms. I fitted an electronic flasher unit as the thermal one was flashing so slowly and it worked ok, flashing both the indicators and the sidelights. If I then switched the sidelights on it locked the flasher relay into the on and not flashing position. The sidelights were trying to earth back through the relay. The same thing happened with the headlight relays which would buzz furiously and you could feel the vibration from the contacts making and breaking.

paddy wrote:It's not the voltage, but the relative resistance of the earth return path versus the return path made by going around the other lamps to their earth. (If anything, more voltage will make everything brighter, including the wrong lamps.) Since a 25W bulb is ony 6 ohms, you will get these symptoms even if there is only 2-3 ohms resistance in the earth, which is hardly anything at all. All of the earths really need to be pretty much perfect to get the resistance down to a sufficiently low level that you don't see these symptoms.
Paddy


That's just about it. You may find that having chased down and cleaned up just about every earth you can find that the symptoms persist. It's at this point you need to walk away, open a bottle of your favorite tipple and leave it until your enthusiasm level comes back up.
It is (just about) worth it. When I finally got the earths and supply connections sorted (till they corrode again, anyway) the old thermal relay started flashing at the correct rate and the (original Lotus) cooling fan doubled its speed. It now actually keeps the engine cool.

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PostPost by: neilsjuke » Tue Oct 06, 2009 7:39 am

Check using a voltmeter from the battery terminal earth using a long lead (battery booster/start lead) to all the earth?s bulb body?s if you get say more than ? a volt at earthing point this will get you in the area. You can do the same on the supply side you may then find some volt drop (ign switch ,Bullet common connector) you could hot wire the supply side of the flasher unit to bypass the ignion side for test.
As the car is not running put a battary charger on to up the volts .
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PostPost by: oldelanman » Tue Oct 06, 2009 8:59 am

As the car is not running put a battary charger on to up the volts


Don't make the same mistake I did. As I had no servicable battery I was using a battery charger as a power supply to check out each circuit in turn, worked OK until I started on the headlamps and then I got the buzzing relays and various other faults appearing. Spent some time checking the earths and connections before I finally realized (getting old you see) that the headlamps require around 10 amps and the charger couldn't supply it - worked OK with low current circuits like sidelamps and indicators. Bought a new battery and everything worked fine.
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PostPost by: ianf » Sun Oct 11, 2009 7:17 pm

Well I got most of the way there and so this morning started the car and checked all was working (still a bit of a pulse of brake light with flasher on but not that bad) and found that the tacho (which kept failing on holiday as well) was pulsing with the indicator dropping from 1,000rpm to nearly zero when the brake lights were on!

I have tightened all the earths on the instrument clamp nuts again and run a couple of test earths and the problem somewhere in all of this has gone away.

Is this just likely to be a further manifestation of the general earthing problem? If there are any other explainations I would be grateful to hear.

Many thanks,

Ian
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