Lotus Elan

Turn signal riddle

PostPost by: steve lyle » Thu Aug 20, 2015 12:50 am

This is a '72 Sprint. It has the federal "1-bulb" wiring for park/brake/turn, where brake and turn signals are shared on the 'bright' filament of a 2-filament bulb. I've searched and learned about the box on the firewall to the right of the column that handles the switching to make this work.

This is a new-to-me Elan - I took delivery about a month ago, and I've been working to resolve multiple wiring problems.

The brake lights work. The turn signals don't, either front or rear. When I flip the turn signal stalk, I can hear an audible relay "click" from the control box. With the brakes on, flipping the turn signal stalk to the right results in the right light going out. But no flash - either at the rear or at the front. Same for the left.

My wiring doesn't match the diagram from the Workshop Manual. The flasher module is a 2-wire unit. The 'B' wire to it is definitely carrying 12v, and the 'L' terminal is definitely passing 12v to the TS switch. Obviously that 12v is showing up at the control box, else I wouldn't be hearing the 'click'. The TS power is 'turning off' the brake light, but going on to the bulbs.

Any ideas, other than replacing the control box? I searched and found a wiring diagram that a helpful soul posted re: how to replace it with DPDT relays. It looks like I'll need to pull the dash to get to it, which looks to be a royal pain to do.

Am I on the right path, or am I missing an easier fix?

Thanks,
Steve
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PostPost by: elanner » Thu Aug 20, 2015 2:04 am

My guess would be a faulty ground or three. They won't be anywhere obvious because Elan electrics don't follow the normal laws of electricity or logic.

If the control box is clicking I would take that to imply that it's working and leave it alone.

If the brake lights are on - there's 12v and a ground, somewhere. If the turn signal is then turned on there's another 12v, and it's probably balancing the brake light 12v, so the brake light is going off. The "somewhere" ground is probably through the turn signal filament and not through the bulb housing ground connector. A potential fault tracking approach would be to see if the brake lights will come on when the 12v wire to the turn signals is disconnected, or something equally Machiavellian. Or just assume that the bulb housing grounds (and any other ground connectors) in the trunk/boot and in the nose are hosed - take them apart, clean and reassemble. Measuring 0 Ohms with a meter does not mean that the circuit is able to carry a useful current.

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PostPost by: steve lyle » Thu Aug 20, 2015 4:33 am

Nick,

With this car's setup, there's only 1 hot wire to the brake/signal lamp filament in the rear. And only one ground. Thus, it can't be a ground issue in the rear, or a bulb issue, or any kind of wiring issue, or the brake light wouldn't function in the first place.

And none of the indicator lights are flashing, but all of the lights function if I feed them 12v directly. So the lamps, sockets, and grounds are all good.

Steve
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1972 Elan Sprint 0248k @ https://www.mgexp.com/registry/1972-Lot ... 48K.30245/
1972 MGB Roadster @ https://www.mgexp.com/registry/1972-MG- ... 842G.4498/
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PostPost by: elanfan1 » Thu Aug 20, 2015 8:10 am

Wondering whether by passing the control unit and putting power directly to the flasher unit will make your lights flash. I'm no auto spark but if that works won't that isolate the control unit as being the problem??

Also wondering if you've also got the difficult to locate hazard warning light switch sometimes mounted on the bracket that holds the bonnet pull handle if fitted just under the dash. The switch is like the glovebox immobiliser switch and is crap, wondering if that's disintegrated internally and might be having an affect on your circuitry?

Probably talking through my rear as usual but perhaps worth looking into?
Last edited by elanfan1 on Thu Aug 20, 2015 8:56 am, edited 1 time in total.
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PostPost by: RogerFrench » Thu Aug 20, 2015 8:52 am

I might be the helpful soul to whom you refer....
In any case, before replacing the DB10 relay I'd test the flasher unit out of the car.
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PostPost by: lotustastic » Thu Aug 20, 2015 12:03 pm

Not sure how the box is wired, etc. but is there a full 12v signal making it out of the magic box from the turn signals going back to the bulb holders? The laws of Lucas electrics suggest that even though there is audible clicking from the TS relay, a less than stellar ts relay or even corrosion/a mouse nest in the box after the relay could be hampering sufficient voltage/current to make it back to the bulbs to make them operable.


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PostPost by: RogerFrench » Thu Aug 20, 2015 3:30 pm

Power comes from the Turn Signal switch to the Hazard switch and the DB10 Relay. The DB10 disconnects the brake switch circuit and connects the flasher circuit, which gets its power via the hazard switch.
You don't mention if the hazard circuit works.
If there's an issue with the flasher unit, the DB10 will click, brake light go off, but there'll be no flashing. That's why I suggest testing that first.
If the hazard switch is goosed, neither hazard nor flashers will work.
I suggest you look at the Europa TC wiring diagram at www.lotus-europa.com. Click documentation and scroll to electrical.
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PostPost by: elanner » Thu Aug 20, 2015 3:36 pm

Interesting.

In a similar vein, headlamps also have two filaments in the same bulb (& three wires) and I had endless fun chasing 12v and grounds around mine because they were wired wrong.

For the flasher, can't you just remove it from the circuit and connect B and L together?

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PostPost by: gjz30075 » Thu Aug 20, 2015 10:22 pm

steve lyle wrote:My wiring doesn't match the diagram from the Workshop Manual.


Nor does mine. '72 Federal Sprint. For what it's worth, I found my flashers get their 12v from the second lug
on the instrument voltage regulator, which really only controls the fuel gauge. 12 v goes into the regulator with 10 coming out the other side. There should be 2 lugs on the 12v side and one of them (mine anyway) feeds
the flasher
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PostPost by: arcangel » Fri Aug 21, 2015 5:35 pm

I spent a fun weekend a couple of weeks ago troubleshooting the non working brake lights and turn signals on my DB10 relay equipped Europa. Neither work shop manual for both my Elan S4 and Europa S2 references the DB10 relay box. To get an understanding of how this elusive relay works, I found a excellent description in the GGLC tech section:

http://gglotus.org/ggtech/relaybox/relaybox.htm

I'm assuming that logic box work the same way for the Elan and Europa. If the relay box clunks when you turn on the turn signals, you're getting power to the DB10 box and the two relays are operating internally when required. If the turn signal lights do not flash at all, there is probably high resistance on the contacts for the relays inside the box which was the case with my non working signals. I cycled the relays, turning the turn signals on and off, probably around a dozen times knocking the crud off the contacts until I got working signals. If you review the article on the GGLC website, the brake light is suppose to go out when you turn on the turn signal for that side. The flashers for that side then start to flash.
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PostPost by: steve lyle » Sat Aug 22, 2015 9:13 pm

Thank you Nick, elanfan, Dave, Roger, Greg and arcangel.

I now have: headlights, horns, parking lights, turn signals and hazard flashers. None of which I had when the car arrived.

The trick for the flashers was knowing about the DB10, and the Europa wiring diagrams. Which enabled understanding that the flasher 12v is fed into it, not the turn signal switch (which is how the PO had it). Feeding green to the turn signal, then hooking the green/brown from the flasher unit to the only visible, unconnected terminal on the DB10 (luck, that), got everything working. Hazards, too. Woo hoo.

Again, thanks to all who provided a piece to the puzzle. Now to bundle everything back together. Maybe after I figure out why the courtesy lamp won't light. And the reverse lights. Those got to be easier, right?
Steve Lyle
1972 Elan Sprint 0248k @ https://www.mgexp.com/registry/1972-Lot ... 48K.30245/
1972 MGB Roadster @ https://www.mgexp.com/registry/1972-MG- ... 842G.4498/
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PostPost by: RogerFrench » Sat Aug 22, 2015 9:25 pm

Glad you got there Steve.
As for the rest...easier? Well, maybe. Good luck!
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PostPost by: denicholls2 » Mon Aug 31, 2015 6:34 pm

Another important item I do not see in this thread: Relays of the period were bimetallic, current-sensing. They open when the current caused the bimetallic strip to sufficiently heat to do so and closed when it cooled again.

If you replace sufficient bulbs with, for example, more reliable LED replacements, the current-sensing circuit may not pass sufficient current to heat up the strip. The result will be the exact symptom you note.

Solution is either to fit incandescent bulbs again or to replace the relay with an electronic one that does not rely on circuit load to "blink".
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