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MG Midget and Sprite Technical - Sidelight electic wowes, only 5volts!

Hi,

I've a problem with the sidelights. The drivers side wasn't working, passengers side all OK.

Checked the bulb, all OK. Used a multimeter indicated only 5 volts present. headlight working OK, 12+ volts all round, it is just this one sidelight which is an issue.

Can anyone give some advice as to tackling this issue?

PS. Does the sidelight need to work for the UK MOT? Headlights are fine.

Cheers
Mat
M Andrews

Mat,
You do not mention the vintage of your car, so my remarks are centered around the RWA models with which I am familiar.

First point: The lowest two fuses in the block are for the running lights. One fuse is for the left front and the right rear, the other fuse is for the right front and the left rear. The circuit is completely separate from the headlight circuit from the headlight switch on. My guess is that either you have a bad connection at the fuse block or else a bad ground wire. If it is only the one front light and not involving the diagonally opposite rear lights, more likely a ground. The ground connections on those is iffy at best. Use your VOM to measure from the center contact for the bulb to a GOOD ground. Better yet, rig up a spare bulb and socket so that you see the results of an actual load rather than the no-load situation measured by the VOM. Plenty in the archives about reconditioning the fuse block.

Second point: Does the light in question merely do marker duty or does it have a second circuit for turn signals? If it has the second circuit, a ground problem frequently shows up as both filaments lighting when the turn signal is on and the marker lights are not.
David "all lit up" Lieb
David Lieb

corrosion
corrosion
corrosion

check the earths

with steel wings expect to find rust where the lights are screwed to the wings, clean and bring them back to bare metal if you can, then paint afterwards with a good primer

also unplug the bullet connectors and give them (all of them each side, dont ask why I know) a good cleaning inside with sandpaper or emery cloth

clean the bullets too*

It will pay you to spend a couple of hours doing all of these at the front of the car

Bad earths or live feeds will drag voltages down quicker than quick

as a final consideration clean the terminals on your fusebox too and inside the battery terminals and the battery posts


*when you clean each bullet it is a good idea to put a hot soldering iron (well tinned too, but not blobtinned) at the point where the wire pops out of it and reheat the solder inside the bullet

careful not to melt the wire insulation though :-)

Bill

Hello corroision my old frind, you screw me up so bad...its the sound of silence....LOL


Sorry, couldnt help it...least I was singing simion and garfunkle and not dacing queen by ABBA.

but yes look at fuses, wireing connections, ground connections, bulb holder/bulb socket, and the bulb its self...remember the bulbs are 12 volt...not 2.3, 3.6, 4.8, 6...but 12 volt


prop
Prop

Sorry, it is a MK4 midget (1500), the sidelight is within the headlamp enclosure.
M Andrews

With the sidelight inside the unit it shares the earth with the headlamp, so actually this piece of diagnostics is useful.

Look at the rear, if the rear is OK then the problem is almost certainly the bullet connector that joins the red wires behind the lamp in question (inside the wheelarch getting covered in crud)
Will Munns

Here's a simple diagram of a lamp circuit. The voltage at point A should read 12v and the voltage at B should read 0 volts if no extra resistance is in the circuit. If there is resistance from a bad earth or poor connection in the circuit as shown then the voltage at point A would read lower than 12v and the votage at point B would read higher than ground. From your description it appears that there is some resistance in the circuit before the lamp since the voltage at the lamp is only 5 volts. It is most likely in the bullet connectors where the power to the side light connects to the harness.
Always ground or earth your meter to another known good point, not through the wiring harness to prevent false readings.


Bill Young

Prop,
I think I could make a good case that they are actually 14.6 volt bulbs ;-)
David "aren't DVOMs wunnerful?" Lieb
David Lieb

I agree with Bill, check each connection voltage with the DVM to a good earth, you should find the fault pretty quick.
14.6V sounds a bit high to me, i would have expected a reading more like 13.6V.
Brad
B Richards

Thanks for all the info.
Problem was caused by too much dirt in the connector from the wiring loom to the front light spur.
Cleaned it all up and lights are now shining brightly.
M Andrews

I rebuild my car 7 years ago. All the connectors were sanded with emery cloth and the loom was new. Last weekend I encountered my fist corrosion problem. It was one of the front connections just under the front valance. The car encounterd les then 10 rain days since rebuild.

Thats how fast it will go wrong. As a pre caution at the rebuild I put in at least 10 extra earth wires. From indicator housings, mainlamp housing, every dial in the dash etc. Probably that saved me from problems earlier.

Bas
Bas Timmermans

This thread was discussed between 20/08/2008 and 24/08/2008

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