Both turn indicators flash, hazards OK - '74 Federal Sprint

[74Twincam]

Gents,

I had all the lighting working properly, and recently switched all my bulbs to LED from the incandescent type. With new, specialized relays to account for the lower resistance, all lighting functioned... for a time.
Now, when I use my turn signals, all four amber lights flash, as if the hazards were on. The hazard switch seems to work just fine.
I've swapped the turn indicator relay and the problem remains- is this potentially a ground fault? The indicator switch in the steering column? Anyone else experience this and have a solid starting point for troubleshooting?

I will start to dig into it shortly but am curious if someone's already dealt with this and can save me some time...

Thank you!
Bill

[74Twincam]

Pardon my typo - a 1972 Elan Sprint... my brain was on Europa time...!

[pharriso]

Bill, do you still have the original DB10 flasher / stoplight relay?

[74Twincam]

I do... suggesting I simply replace and test? I’ll try it, ...curious what’s the theory behind that suggestion?

Thanks Phil,
BR

[Andy8421]

That DB10 relay is a surprisingly subtle design. It allowed Lotus (and other UK manufacturers) to make use of their brake lights as indicators without requiring much change to the wiring. This gentleman has done a really good writeup on what is going on:

https://www.gglotus.org/ggtech/relaybox/body-relay.htm

The key point to remember is that the indicator stalk isn't in the flasher circuit, it just switches the correct relay on (there are two) in the DB10. If it all used to work, and now all four lights flash together when you use the turn signal, that would imply either:

1. Both relays are on (check to see if pins 8 and 4 on the DB10 are being energised together) in which case the wiring, hazard switch or indicator switch are faulty.

2. The innards of the DB10 have corroded and stuck in some way.

If is it 1, I would first look at the hazard switch - it has more bits to fail than the indicator stalk.

One final point - you said 'all four amber lights' - I thought the federal Elans only used the red 'brake lights' at the rear for both brake lights and indicators - that's the whole point of the DB10

Second final point - There is a wrinkle in using low current bulbs in some configurations as the dash repeater light can use the un-energised side (ie the left side bulbs if you were indicating right) as an earth. This can cause strange behaviour with LEDs. You are sure everything worked OK after you changed the bulbs for LEDs and it has only recently developed this fault? A quick test (if you still have the old bulbs) is to swap them back for the LEDs and see if the problem goes away.

[pharriso]

I do... suggesting I simply replace and test? I’ll try it, ...curious what’s the theory behind that suggestion?

Thanks Phil,
BR

Just asking because it's way more complicated if you still have the DB10, as you can see from Andy's response.

[74Twincam]

I wanted to just get back to you on this- still working on it and, yes, I do still have the DB-10 in place. I've done the same on my Europa, but come to think of it, had replaced the DB-10 in the Europa with a new one (prior to fitting LED's). The new DB-10 is a solid state replacement so potentially isn't going to exhibit the same issues as the original Lucas piece.
The nice thing is I can swap units from one car to the next as a quick check too (after some under-dash contortions).

Good sanity check and fantastic resource, thanks Andy and Phil!

[74Twincam]

SOLVED!

After checking multiple bulbs at the corners and wiring, grounds, etc.- and buying a new DB10 relay (solid state) from British Parts Northwest, installing (assume the Lotus Position under the dash)...If you do this, note that you'll need to trim off one of the mounting flanges on the DB10 box to allow it to fit up against the firewall, just note the old relay. I also switched the hardware from my original relay and reused the blade connectors to fit the stock harness.
It turns out as I was sitting there on the floor checking switches and getting the wiring back together, I noticed the green indicator bulb on the Speedo wasn't flashing along with the signals. From the driver's seat I don't always see that. I pulled that incandescent bulb out and left the socket blank and BINGO- signals operate as they should.

I'll try an E10 size LED bulb in the gauge there and see if it comes back, otherwise the clicking of the relay will be enough..

Thanks again guys for the input and help, always appreciated!

Bill

[Andy8421]

Bill, I am afraid replacing the dash repeater with a LED won’t work.

The easiest fix is to ditch the LED indicators and go back to using the incandescent bulbs - I hope you didn’t throw them away….