1972 911T Hazard Lights Query

[sfh3l]

Hi Chaps,

It's been quite a while since I posted on here. I am now out the other side of a major home rebuilding project and once again have some time to spend on my cars

I had experienced one or two electrical gremlins on the old car in recent use. Last year this culminated in a non-start on the morning I was due to leave for the Le Mans Classic. My Boxster deputised extremely well and I got down to diagnosing the issue on my return. It turned out to be a very crusty engine fuse board that was interupting the supply to the ignition. I bought replacement boards for both the engine and main fuse boards from Classic Retrofit, working on the basis that modern blade fuses would be far more robust than the crusty old bullet jobs, held in by ever lazier brass tangs.

I immediately replaced the engine board and all was well there. Other stuff got in the way and I have only just attended to the main board.

Before changing the main board, I had been experiencing some lighting issues that looked very much like an earth problem. I stress that all the lights worked as intended on the outside of the car, with no cross-contamination between side lights, brakes and indicators you often see on old bangers. The only weird thing I could not trace or rectify was a tendency for the two green arrows (indicator indicators) on the rev counter to play up. When the indicator was first engaged, the lights flashed as expected, but after a few seconds it would go from one crisp and bright flashing light to two dim lights, flashing together. All the while the indicators outside were working correctly. I was keen to sort it, but equally not urgently, as the lights were functioning corectly. I know my sidelight/indicator units are a bit crusty and suspected that an earth was not all as it should be in a wheelarch somewhere.

So I changed the board today. All good and an excellent product in my view. One small slip caused main and dip beams to come on together but I soon rectified that and everything is working correctly. The indicators now function with none of the silliness they were giving before, which is great. However, the Hazard Lights now no longer function. ??? There is no clicking from the relay when they are enganged and no lights flash, either outside or indeed in the dash switch or rev counter. Indicators work perfectly, but if you engage the Hazard switch while the indicator is on, it kills it. No fuses blow, and the indicators work again when the Hazards are swithced off.

I have not in any way disturbed the wiring to the dash switch for the Hazards while doing this. I did remove the two relays that are mounted one above the other beside the fuse box to ease the job, but both are back in pace and correctly located. I also wiggled both while the Hazards were switched on, just in case they were not engaging into a dirty plug (not even sure if either of these is the Hazard relay in any case, but just checking the things I've messed with).

SO - my question, after a very long preamble, is what you think this might be please? I suppose the Hazard relay might have failed, but it seems a bit of a coincidence and I had checked it last weekend when I started the car up and used it for the first time this year, so the failure is very recent if it isn't directly related to what I have done with the fuse box.

Aside from a pretty tedious job on the old 911, where some of the wires have very little slack, the fuse box was a decent enough job and the only oddity I noticed was that my car has a blue and black wire detached and located behind the fuse box in a connector, which clearly was one day part of the system but has long since been removed by somebody and made safe.

Any ideas, you clever lot?

Thanks in advance and wow, it was nice to be bouncing back down the road on my test run this afternoon!

[hot66]

I'm crap at electrics, but does the hand brake warning light still come on and flash with the handbrake pulled up ?

[sfh3l]

Hey James,
Thanks for responding and that is a very intersting question.
I've just checked the car and, with ignition on, the handbrake warning flashes correctly. The handbrake warning doesn't interfere with the indicator warnings, as these flash themselves when indicators are used and with the handbrake if the handbrake is also on.
But no, the handbrake does not flash when the Hazards are switched on - they kill it, just like they do the indicator warnings.
I am sure people are going to tell me this is an earthings issue, and indeed that's what it feels like to me. However, I don't get why it should have triggered this very strange behaviour when the same earths did not do this before I changed my fusebox.....
Has my answer helped or hindered your diagnosis?
Cheers, Sam.

[Nine One One]

There was a similar thread on the tell tale lights for the indicators playing up recently, and somebody posted this link from Pelican........
https://forums.pelicanparts.com/porsche ... avior.html

It will no doubt be a GROUND/Earth issue. The new fuse board may have helped with the indicators, but now perhaps they are getting a better voltage, perhaps it is showing up the fault with the hard lights now instead?

[coomo]

The "twin flashing green lights" were an issue with my hotrod build.We installed a brand new loom.Freshly fitted.Despite everything being as it should we could not get the indicators working correctly.Replaced 3 relays.Until we were told to "ditch that shite Chinese relay and use only a genuine Hella"
That fixed everything.
I would do this.Then refit every earth.Pull the tags from under the dash.Clean and refit.
Same for all earth tags on body.Just because "It worked yesterday" doesnt mean it will today.
The final issue just maybe a 50 year old loom.

[cschmueck]

agree with coomo. I posted that Pelican link. It took me three years to figure out that issue, I have tried 3 different replacement relays and all of them triggered various combinations of odd flashing of hazards, indicators, handbrake light and the lamps in the instrument. I switched back to the original Hella relay and applied the ground bridging described in that article. Basically my original relay had a fault with a secondary coil in it and still does- the Y ground bridge overrides that coil.

[sfh3l]

Thanks Chaps,
I've not changed the relay and am sure that it is the original one, so entirely likely the secondary coil is weak or dead altogether.
I will make up the 'y-piece' as described in the brilliant Pelican article and see what that brings.
It is strange that the symptoms have changed markedly since dealing with the fuse box, but I suppose it is very voltage dependent and better connections might just be triggering different behaviours while correcting other errors. We'll see.
If the hazards hadn't been working perfectly before the fuseboax change, I'd suspect the hazard switch first as culprit, but I've gone nowhere near that or its connections, so it would seem highly improbable that it has chosen this precise moment to fail on me.
Thanks for all your help and I will report back for the record, if and when I manage to sort this out.

[sfh3l]

OK, so thanks again for the really helpful comments and responses.

I popped out to Halfords and got the various tags I needed and made up the 'Y piece' for earthing the indicator telltales. I then fitted them and made safe the common wire that these new earths replaced.

This didn't actually change the non-funtioning hazards, or the strange way the hazards interupt the function of (actual) indicator, indicator telltale and handbrake telltales in the tachometer.

So I scratched my head and went back to look at the new fusebox for inspiration. The Classic Retrofit box comes with a helpful LED that glows when a given circuit is powered, but broken, by the fuse or some other interruption. Lo and behold, fuse 2, which I had set as a 5-amp one, showed as blown. Initially, I thought the earthing suggested for the telltales was perhaps a bum steer and my new wires had actually just shorted the live supply to earth, but then I reassured myself that this had actually failed prior to my even knowing about the telltale earthing and this could not have been the reason.

So I replaced the blown 5-amp fuse with a 7.5-amp one and all is now well.

Please correct me if you think I'm wrong, but perhaps 5 amps was just too low a rating for the 4 x indicator bulbs (21W I believe) on the hazard circuit, plus whatever else might be occupying that circuit, plus a no doubt tired relay. It may I suppose have been the result of my accidentally shorting something while buggering about, but that was all with the batteries isolated - you only have one auto electrical fire in a lifetime and mine was over 40 years ago on my old BMW, but the memory still burns brightly and makes me pretty cacreful as a result !

So now everything works as it should, and in all the different permutations possible.

As an aside, my feedback on the Classic Retrofit products is that they are first rate. The engine fuse board was easy, both to get at and to replace. On my car it was essential as my old one was a crusty old thing that had no place trying to pass reliable current anywhere. It had been responsible for some perculiar running issues and ultimately a complete non-start on a crucial journey. The front box was more of a sod to do, simply because of location and the relatively tight wiring constraints. However, I did it in less than 3 hours and the end result is a much happier little motor. And a happier me !

Thanks again for your help guys. This forum really is invaluable and the collective wisdom is fabulous.

Anyway