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

I have followed the lead from Roger on changing the indicators for duel filament side/ DRL/indicator fittings (maintenance and servicing).

I followed his installation of switch back led bulbs, double filament holders and a relay.
I picked up the main power feed to the relay from the heater fan fuse which feeds nothing else, and is hot only when the ignition is on.
I picked up a feed from the side lights to the relay, to switch the DRL's off when the lights are switched on.
I ran a line from the relay to earth and another line to the DRL's.
The indicators were run into the existing loom and are independant of the other insallation.

All worked fine, the DRL's lit when the ignition was switched on, the indicators kick in and run fine including the hazards,the DRL's go out when the lights are switched on.

So far so good.


On a run out today to get petrol at £1 a litre I decided to check the opperation of the lights on the car in front at a set of traffic lights. This is where I noticed that when I turn the lights on the speedo jumps to 40 mph and then returns to zero (as I was stationary). This has me baffled as the speedo had nothing to do with the installation and wasn't touched.


Any ideas chaps?? 1997 +4.

Not familiar with the new installation as a whole but does the relay employed have diode quenching, as it should if not OE. A shot in the dark but without such the back emf from the relay coil may be upsetting things.

Thanks Richard, I don't think that the relay had diode quenching so I have ordered one, will keep you updated when it arrives.

Fingers crossed.......

Update so far,

I have disconneted the relay, this leaves the indicators all working fine and no jumping of the spedo when the lights are turned on.

This points rather strongly to the point you made Richard.

Thanks again...

Rob.

Latest update,

Relay with diode arrived today after the first one was lost in the post.

Fitted it this afternoon and some strange things happened, no jump on the speedo but the fuse blew on the off side side lights ( this is the side I picked up the feed for the relay ) this led to the drl's staying on as the relay had no feed across the terminals to swich them off.

I changed the fuse ( 5 amp ) for a new one as I wondered if the fuse was due to blow any way, tried again but alas when the side lights were turned on the fuse blew again.

I put the relay with no diode back on and the fuse was ok but the spike returned, this rules out the possibility of a dead short in the wiring I think.

With the relay disconnected all works well, indicators, hazards, side lights and head lights.

The question is why does the relay with a diode blow a 5amp fuse, when the one with no diode is fine but produces a spike on the speedo.

I now need to go out tomorrow and buy a handful of 5amp fuses.

Any ideas chaps??
as i'm thinking of putting things back as they were and leaving all alone.

Maybe.... Now that you have a diode connected across the coil it is polarity sensitive. Do you have the anode side connected to ground?

Hi Roger,

I have the feed from the side lights going to terminal number 85 and the ground going to 86, would this be correct?

other than that is there any other way of checking?

Thanks for your help mate

I must just add that the relay was advertised as suitable and used by many roadster morgan owners, so I gather this is the correct one to use.

My understanding with the Tyco type relays is that 85 is the anode so 85 would be ground but I have seen relays with them the other way around. I am not an expert here....
Generally there is a little picture on the side showing the diode orientation?

Hi Roger looking at the picture I have a loop connecting 85 to 86 with an arrow head pointing toward 86 would this then indicate that 85 will be ground? If so, it would appear that I have the wiring the wrong way round because at the moment I have 86 as ground.....

I am not an expert here either...