Headlamps w/ no Taillamps; 4-Way Flasher w/ no Turnsignals

[Kip]

Hi all,

Been working on my neglected '69 S4 DHC. I've got it starting and running (woot!) and am ready to register it for the road. Only problem is I can't get all the lights to work. Here's the situation:

• Headlamps work when the headlamp switch is engaged and turn off when the switch is disengaged
• Tail lamps and side markers do not work regardless of the headlamp switch position
• All lights work when the hazard switch is engaged (front left and right ambers, rear left and right tail lamps)
• None of the turn signals work (Front or back, left or right)
• Brake lights do not work
• Interior light works
• Two main fuses in the engine bay are not blown
• The ignition warning light on the tach lights up when the key is in the "on" position

I'm confirming with the previous owner whether or not all the lights worked previously when he was driving it, but wanted to run this by all of you:

I found the ignition switch is missing a wire. It's the green wire that connects ignition switch position 4 to the brake switch and indicator switch. Seems like the culprit. Tried to chase the wires to find the common connection point (a 4-block bullet connector), but haven't found it yet. But since the missing wire is connected to position 4, would it impact the lights when the car is running? Position 4 is the "accessories" position that allows the accessories to work when the engine isn't running, isn't it? Does that position do anything when the car is running? Any direction/thoughts would be appreciated. I've spent too much time looking at the wiring diagram and think I'm missing the forest through the trees or the wire in the loom, as the case may be.

-Brad

[h20hamelan]

The wiring diagrams are around. Where do you have voltage, do you have a electrical trace device?

[Kip]

Appreciate the response.

I have a good, color-coded wiring diagram (from this site, I believe) and the Lotus Repair Manual. I've spent a lot of time digging through it. I haven't pulled out the multimeter yet, but know I have power at the ignition switch and dash. The disconnect is somewhere between the switches and and the lamps. Some power makes it to the RB10 relay (hazzards work), but not all (turnsignals and brake lights don't work). That's what brought me to the missing wire on the ignition switch on position 4.

Any thoughts on whether position 4 is active when the engine is running or whether it's only active when the engine is off and the key is in position 4? Any thoughts on the location of the 4-block bullet connector that feeds switched power to the brake switch and turnsignal switch? Unfortunately for tracing wires, my wiring loom is wrapped/taped, so tracing the wire from the brake switch upstream will require unwrapping it.

-Brad

[HCA]

With greatest respect, you are not only in what sounds to be a complete wiring mess, and I detect that you might not be well enough versed in auto-electrics to sort it yourself. Do you have anyone locally who understands this stuff?

Of course the accessory position is live when the ignition is switched on - what would be the point of it not being so?

There is a green wire on the accessory post of the ignition switch. But it does not go to the brake light switch. It will go to the radio and another to a fuse powering a cigar lighter and interior lights.

The wiring to the brake light switch is incorporated in that of indicators, heater switch, wipers, washer et al. The source is from a fuse on the switched 12V and not directly from the ignition switch. This green wire that you are fixated on is maybe to the radio and if so, it goes to position 4. If on the other hand you have a green wire that is powering the various switches, do not, whatever you do, connect it to the ignition switch - doing so is auto-electrics russian roulette!

[Andy8421]

Good idea to confirm whether the lights used to work with the previous owner. If so, very unlikely that the wire would have vanished. Your problems would be elsewhere.

The DB10 relay (2 relays inside) is a surprisingly subtle design. Given that the lights work with the hazards, it is unlikely to be an earthing problem at the light units (the usual problem), so as a first port of call I would suspect the DB10. There have been threads on here (and also the MG forums) about how to troubleshoot these.

Good luck.

[Kip]

@Andy8421
Interesting about the RB10 being two relays. I had discounted that as the problem because the hazards work and go through the RB10. But if it is really two different relays, theoretically, half of it could fail and create the situation I'm seeing.

@HCA
Appreciate your assessment and feedback. And while working on this car is new to me, I've been working on my own cars for 30+ years. This car was bought new by my stepfather and professionally redone about 20 years ago. Point being, I have the advantage of knowing it's previous owner and most of it's history. Regardless, I always have room to learn.perhaps I'm reading the wiring diagram wrong. But if you look at the attached image, I'm seeing the green wire from position 4 on the ignition switch trail to a 4-block connector that splits to the radio (to your point), but also to the brake light switch and indicator switch. That's why I'm troubleshooting it (not fixated). If I'm reading it wrong, I'd appreciate the education. I'm assuming wiring diagrams are universal, not unique to British marques versus Italian or American ones.

-Brad

[HCA]

I owe you a big apology Brad

I did not appreciate that there was one of those frightful RB10 relays involved until I read Andy's post AND of course there is the 'Lotus' factor that I did not take into account - this is where much of their auto wiring was a law unto itself and changed depending on the quality of ganja around at the time.

Why they would want to put the brake and indicator switches onto an accessory terminal is just plain crazy, but you are right, this is what they did on the diagram you attached! I guess that all you can do is pull it apart and follow each wire and see if any are unhooked or misplaced. As for the RB10, I agree with Andy, if it is not earthing and if anything is going to wrong it will be in there.

If I were your neighbour, I would offer to rewire the car for you...

[Kip]

No worries, mate. I wasn't entirely convinced I was right or you were wrong. After spending too much time following that diagram and trying to track wires while in the Lotus position with my head in the foot well, I wasn't sure I was reading things right. I agree, btw. Why would your brake lights be tied to a switched power source off the ignition switch? Must have been some good smoke the day this one rolled off the line. Hahaha

The good news is the wiring looks clean and properly color coded. That should make tracking easier. Appreciate the ideas and feedback from you all. I'll dig back into it next week and see what I find this time. I'm open to any further thoughts or ideas, so let me know what you think.

-Brad
.

[Craven]

I think this would cover your ignition switch most are the same.
May help.

[Kip]

@Craven

Awesome! Thanks. That confirms that the aux/accessory plug (,ignition switch pole 4l is hot when the engine is on. Thank you.

-Brad

[phil1800]

Have you checked your fuses? If you are the analytic person, I think you are, forget my advice. If you are like me, check if your fuses carefully. I had a similar issue, with no headlamps and no rear and brake lights. The fuse soldering was bad, but when measuring the fuses in the fuse box, they seem to be fine. The pressure of the Voltmeter ‚tips‘ was enough to restore the connection…… Dumb

[Kip]

@phil1800

Good call. I did a visual check. Fuses are not blown. The headlights work, but the taillights don't. Since I believe they run through the same fuse, that confirms my visual check and negates
the possibility of a similar situation to yours (how maddening was that, btw?!?)

You did catch me though. I think checking fuses was the third thing I did, instead of the first. I sometimes have a bad habit of thinking zebras, not horses, when I hear hooves.

-Brad

[Kip]

A quick update and a word of warning. After more troubleshooting, something wasn't sitting right. There were too many discrepancies between the (pretty clean) wiring in my '69 Federal DHC and the wiring diagram found in this thread: https://lotuselan.net/forums/viewtopic.php?f=38&t=48600. I compared the PDF wiring diagram to the one in the original Lotus Workshop Manual (March 1970). There are some differences. Specifically, there are differences in the ignition switch circuit that controls switched power and no DB10 relay. Don't get me wrong. The PDF in the other thread is a great resource. I prefer it to the manual version because of the color-coding and portability (nice having it on my phone when I'm in the Lotus position). I think it will work 90% of the time or more. But for my version of the car, it wasn't spot on and led me down a path where I was chasing connections that didn't exist.

With new found knowledge of the circuit paths, it appears I have a switched power problem. All of the devices powered by the "green wire circuit" are not receiving power. Time to get out of the footwell and start tracing from the fuse box.

-Brad

[Kip]

@HCA

The wiring to the brake light switch is incorporated in that of indicators, heater switch, wipers, washer et al. The source is from a fuse on the switched 12V and not directly from the ignition switch. This green wire that you are fixated on is maybe to the radio and if so, it goes to position 4.

You, sir, are correct, based on the wiring diagram from the Workshop Manual. It also explains why there was no unattached green wire behind the dash. The open post is for the radio, which is sitting in a box in my storage room.