Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Speedo jumping.

Morning all,

Well the relay arrived today, I fitted it and tried all as before, spike still there all other aspects working as normal.

I then took the car for a run (in the rain) speedo still jumps whilst driving when the lights are switched on (speedo works fine).

On returning I parked infront of the garage and checked all the indicators and hazards, all working ok DRL goes out as indicator takes over then returns once the signal is cancelled.

Tried the side lights again and got a spike taking the speedo up to 50mph.

I think I will run it passed BHM later this month, I am fast reaching the point where I think I shall reinstate the original indicators and run with no DRL's.

Does this article help ? http://geoffsshed.net/drls.html

Sorry to hear that Rob, you have put a lot of effort in. Is it a big deal though to have a small interference spike on the speedo whenever you turn your lights on? I agree, disconnect for now and ask the auto electrician on the 29th if there would be any long term issues running it like that.

Those DRL’s are beneficial these days on our crazy roads……

One final thought from me and then it’s over to the auto electrician.
I am wondering exactly where the new relay is physically positioned. If it is behind the dash and close to the speedo itself or, in close proximity to the speedo pulse wiring, could it be an electro-magnetic pulse is induced into the speedo or wiring at the moment of switch on? Could be worth mounting the relay on some extended leads so that it is well away from the loom and instruments to see if problem persists?

Thanks John for your input I shall study it tonight.

Roger, I think this is the best line to take with this, talk to the people that know a whole lot more than I do and see where it goes.

I agree that DRL's are a great help on todays roads so I shall try to keep them if at all possible. Not too sad a loss from a money point of view as I will have a brand new set of stop/tail lights should I need them. Not to mention 20+ 5amp fuses, and my new found understanding of relays. MUST REMEMBER 85 IS GROUND.

I would be very interested to know the root cause of this spike at the end of the day....

Hi Doug,

The relay is in the engine compartment mounted on the tool box housing at the front, the engine management box is mounted on the top of this tool box.

That idea did cross my mind so I moved the relay to about a foot away but this made no difference. I also had led bulbs in the wing top mounted side lights (where I picked up the feed for the relay) so I replaced the original bulbs which are 5 watts each as I had an idea that perhaps the led's didn't have enough resistance and allowed the spike to happen, but this made no difference either.

So we are now at the point where I have run out of ideas.......


Rob....

Thanks for replying Rob. I think this has now been flogged to death so look forward to hearing if a solution is found in the future. Best of luck.

Good morning all,

The latest in the saga is as follows:

Took the car for it's MOT today and as luck would have it Jim the auto electrician was testing today.

Had a good chat with him and he said that a spike on Morgans of a certain age is not unusual and he has seen some that spin the needle right to the full extent of the speedo and back when putting any load on the system (heater, radio, lights etc), following this it doesn't happen for a while so it's an anomole of some cars. Couldn't explain why it has just started however!

The DRL's were disconnected at this point but he was interested to see how they work as many owners have asked about DRL's and they (BHM) were trying to incorporate it within the head lights, and having problems with the n/s and o/s being two different circuits.

We connected the DRL's via the relay and guess what, no spike this time, so this convinced Jim even more that it is nothing to be concerned about and the chance of any permanent damage to other components is nil.


A note to Roger I told Jim at BHM that the idea was yours and that I couldn't take any credit for it, he was very interested about the bulbs, light fittings and the simplicity of the wiring and said that they may well use this method if future owners ask about it.

Oh! and by the way it passed the MOT. It may be a comfort to future owners to know that a spike on the speedo is quite a common thing.


A BIG thanks to all that have taken this journey with me and given me some valuable input.....

Rob...

That’s really good news Rob. Sorry you had so much hassle. I don’t think later cars will have the 'feature'. I believe my car uses the later generation Carebont electronic speedo so perhaps it has a better noise tolerance. Everything else we did was the same (other than I didn’t use a relay with a diode as there was no switching driver electronics to protect or worry about…. )

Enjoy your DRL’s

Following this post, I have tended to keep an eye on my speedo when starting and surprise, surprise on just one occasion last week, it flipped up to 50mph. Hasn’t done it since and I have done no electrical mods on the car. So that seems to back up the theory “they all do that” (sometimes)