Lotus Elan and Lotus Elan Plus 2 Forums

Here's the reason for asking about R&R'ing the DB10 relay.
lotus-electrical-f38/db10-relay-t38794.html

All turn signals work fine, the right side though is a bit slow. 4 way hazards work fine, brake lights work fine,
regular lights work fine.
However, the right hand side turn signals will no longer work when the brake lights come on. If the
turn signals on the right side are flashing, and I step on the brake, the signals stop flashing and neither
the rh brake light nor flasher (same filament) work. Releasing the brake makes the rh turn signal work
again.

I swapped out both flasher units, ie, the 4 way hazard and turn signals. No change. With an ohm meter, I
went from all four light sockets to their respective grounding points to the chassis and I have 0 ohms.
I fixed a dodgy DB10 ground and it seemed to improve things but not to where it should be.

I have a feeling the DB10 relay is at fault here.

Any thoughts on anything else with this problem?

I would dismantle and clean and reassemble the rear right hand light assembly and its earth all the way to the chassis. While it may test as zero ohm when not flowing current it appears to develop a significant enough resistance when flowing the brake light current to stop the turn indicator.

You could verify if this is actually happening by testing for the voltage of the nominal earth at the body of the housing at the turn indicator bulb when the brake light is on.

cheers
Rohan

Rohan, the housing was re-chromed about three years ago and is spotless, like new.
So, to be clear, I'll be checking for a good ground when the brake lights are on, correct?

Rohan is correct even a 0.5 ohm resistance on a 22W bulb approx 2A would cause a volt drop of approx 1 volt it may well pass the minute current a DVM puts out on resistance setting but at a few amps it may be a problem
Ian

Yes corrosion at any of the joins between the brake light bulb and the chassis may raise the voltage of the housing the turn indicator sits in when the brake light current is flowing. The corrosion in a join can act like a semi conductor and show no resistance at low current but have significant resistance at higher current loads.

cheers
Rohan

This is a Federal car, and the Brake and Flasher share the same bulb and filament. In normal operation, when the flasher is working, the brake circuit is disabled. This is so even if the flasher is started while braking; the "brake" light starts flashing.
This is controlled by the DB10 relay, which was, I believe, only fitted to Federal cars.
I write this only to suggest that Rohan and Ian may not be familiar with this item of jiggery-pokery. I am, having built my own substitute which is installed in my Federal Europa TC.

You don't in your original post say if the front flasher stops when you brake, or only the rear. I would expect both to stop, and if so I think you have 2 connections swapped on the DB10. In its at-rest position, the feed from the brake light switch is directly connected to both brake lights, but turning on an indicator flips the relay to disconnect the brake feed and connect the feed from the flasher. Since yours is doing the reverse of this, I suspect the right turn wire from the indicator switch is wrongly connected.
I don't have a diagram for a DB10 in an Elan, but there are superb Europa diagrams at http://www.lotus-europa.com . Click documentation then scroll down and you'll see Federal Europa diagrams. I don't expect the Elan is much different.

Or, then again, your DB10 isn't working, but you know how to build a substitute.

Hi Roger
No I was not familiar with this federal system setup of using the brake light bulb also for the turn indicator. i knew they used all red lenses but i assumed they still used separate bulbs for turn and brake. What goes in the place where the separate turn indicator bulb was ?

cheers
Rohan

Rohan and Roger, thanks much for your input. Today, with some help, we were able to use a probe on the
wires BEFORE they reached the rear light assembly pod, thus eliminating the whole pod and bulb.
Failure still occured. Keep in mind this all worked for the last 38 years (since I bought it) and only started
failing this last month. The DB10 has never been out of the car and the wires never disconnected from it,

That said, the corrosion could very well be at those DB10 connectors. (ho boy

The front flasher also stops (and goes out), along with the indicator at the dash (goes out).

Roger, I'll double check connections; I'm following 4 different wiring schematics now to get what my car has.

Attached is a pic of the rear lamp assembly with the dual filament, 1157 bulb.

Rohan, the photo shows better than I can how the light is arranged.

Gjz, I hadn't realised it had just stopped. I now suspect the DB10 has either stuck, or has sticky contacts. You could try taking it out and bench testing it. Removal and replacement are not easy, I know!
Good luck.

Greg, the attached may be handy:





Check the ground to the case first; Good luck!

Hi,
To checkout ground connection simply make a direct connection with a suitable jump wire between the battery neg terminal and the metal case part of the bulb.
Ron.

Thanks guys! I'll jumper in direct grounds, to be sure. Thanks Phil, another sheet to laminate.

Update: running new grounds right to the battery didn't change anything.

However! I located an NOS DB10 relay, pulled the wires off the old relay (still mounted (ugh!)) and jumpered
over to the new relay and Voila! All signals and lights work as they should! Now begins the ugly task of
R & R'ing the relays.

Thanks guys for all your help!