Rear Fog Lamp Wiring

Right,

my 90 passed its MOT the 1st year without a foggy fitted, i tried to wire one up but was lazy and didnt get round to it, then the next year the MOT man failed me on it not working etc! so now that its on the record, i have to do something about it.

ive been using my multimeter thingy on the resistance setting (ohms?) and get some readings on both sides of the switch and the tell-tale. following the red/yellow wire to the back where i get nothing. does this mean that there is no connection? or am i reading the meter wrong? im getting numbers like 0.2-0.9 etc. i took this as it was working from fuse to tell-tale. but am now unsure.

also at the rear, i take it i plug the red/yellow of the lamp to the red/yellow of the loom and then earth the lamp using the black wire? or do i connect the black to the other black off the loom? ive looked behind the cover in the rear inside where all the wires are. nothing seems out of place.

any thoughts on the whole curcuit?

quickly losing patience and thinking of hnding it over to an auto-leccy

G

Griffdowg said:

Right,

my 90 passed its MOT the 1st year without a foggy fitted, i tried to wire one up but was lazy and didnt get round to it, then the next year the MOT man failed me on it not working etc! so now that its on the record, i have to do something about it.

ive been using my multimeter thingy on the resistance setting (ohms?) and get some readings on both sides of the switch and the tell-tale. following the red/yellow wire to the back where i get nothing. does this mean that there is no connection? or am i reading the meter wrong? im getting numbers like 0.2-0.9 etc. i took this as it was working from fuse to tell-tale. but am now unsure.

also at the rear, i take it i plug the red/yellow of the lamp to the red/yellow of the loom and then earth the lamp using the black wire? or do i connect the black to the other black off the loom? ive looked behind the cover in the rear inside where all the wires are. nothing seems out of place.

any thoughts on the whole curcuit?

quickly losing patience and thinking of hnding it over to an auto-leccy

G

Click to expand...

When I fitted a fog lamp I ran a wire from the fuse box to an halfords on/off switch and then ran a wire from switch to lamp. earthed lamp to chassis and that was it. If a lamp is fitted it must be working. hence the reason the MOT man failed it.

did your switch have a tell-tale? if i take it off though it will fail as its later than 1980. maybe i should run a new wire from the tell-tale out the back somewhere to the lamp.

The way I'd do it would be to turn the ignition on, turn the dipped beam on, an turn the fog light switch on. With the multi meter set at DC volts on a voltage setting higher than 12 volts, connect the black lead to a known earth and touch in turn the red lead to either side of the fog light switch, if the switch is on the you should get a 12V reading on both sides. If this is OK then go to the back of the vehicle and connect the black lead to an earth again and with the lights on an the fog light on touch the red lead to the fog light lead, an again if everything is hunky dory you should have a reading of 12V.

Reet then while I was riting that it occurred to me that you might think you've got a short in the cable between the switch an the light, wot I'd do there would with the lights an everything turned off make sure the light end of the wire isn't connected to earth either through the bulb or by accident, connect the black multimeter lead to a known earth and the red lead to the switch end of the wire, with the multimeter set to read ohms or the buzzer. If you have got a short you should get a reading or buzz from the meter, if you do get a reading flick the switch to find out what side of the switch is earthed.

Griffdowg said:

did your switch have a tell-tale? if i take it off though it will fail as its later than 1980. maybe i should run a new wire from the tell-tale out the back somewhere to the lamp.

Click to expand...

Yep it lit up when it was switched on.

Reet havin read it all again, its occured to me that you may think the wire is broken somewhere between the switch an the light, an like you say you should get a reading or buzz if you connect both ends of the wire to the multi meter leads.

If there is a break have a look at the connector plug that joins the chassis harness to the harness coming out of the bulkhead. Then the connector behind the drivers side bit of tin that covers the rear light wiring then the connectors on the other side. You could check for continuity in the harness that runs down the chassis rail an the harness that runs between the two bits of tin and across the rear crossmember.

cheers Grunt, will have another look in the morning. along with another go at the brakes.

G