Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Sidelights = FIAT-like electrics

I have a strange problem which is probably easy to diagnose but difficult to find. My 1997 Plus 8 drives like a dream until I switch my sidelights on. Various things happen, but the worst are:
1) The engine starts to miss when under load - this never happens otherwise
2) The fuel guage reads about a sixth of a tank higher
3) The speedometer goes wild, either:
a) if I am stationary it sometimes shoots to about 80mph then back to zero and stops working. I need to restart the car to fix this.
b) if I am driving it appears to add approximately 10-15 mph onto my speed (but can go higher) and wanders even if I am holding a constant speed

None of this seems to happen when I have my headlights on... which is strange because aren't my sidelights still on???

Any thoughts? I guess I have a short somewhere, but how do you start looking?

This sounds like an intermittant faulty connection which is causing spikes of power, which upsets the electronic ignition and the speedo sensor. Is there any sign of a dull sidelamp? - or any flickering (best noticed in the dark). Are the panel lights working OK??
I would start by cleaning the sidelamp fuses, and the contacts in the switch, since this is easy to do. Beyond that it gets much harder. A bad earth is often to blame, so check the sidelight earths. My gut feeling is that arcing at the switch could cause the speedo flutter, but not so sure about the misfire under load. That's an odd effect.
Arcing can cause a gunpowder smell, so sniff around the steering wheel cowl and under the dash. Good Luck.

Thanks Dave, I will give it a good look over as soon as its back from Steve Simmonds where its getting a well earned new roof and improved sidescreens

Why not ask someone at Simmonds to have a look while it's there? It might be a quick fix, and a few pounds' labour time by someone skilled with car wiring might save you hours of troubleshooting at home.

Nigel

yes, I can do that .. Steve is already fixing a rear tailpipe bracket that has sheared under fatigue.. currently being supported by a French jubilee clip! Sacre bleu!

Suggest you do the simple things first, as above clean up fuses but I suspect some bodge wiring somewhere with probably a stray earth, also good to ensure the earth lead is secure, a chafing wire is another possibility it doesn't take much to cause a problem.

Steve is always changing dashboards and likes a poke about the electrics so I would concur you ask him to have a look whilst it is in there.

Chris444