wiring - i hate it !!

[Fizzy]

again, this is with regard to my mates 1973 MK IV spit.

had a brief sort of look at the wiring, as basically nothing works on the car. this is bad news, as niether of us can get our heads round it, i hate messing with wiring with a passion. its not even just that things dont work, some things work wrong, or make other things work wrong. it is all lights though, so at least we can see if we're making progress. i have access to a multimeter, but no real idea how to use it, ive never had to.

first thing that springs to mind is indicators. we can hear the flasher unit, clicking at at least twice the speed it should be, but cannot see it anywhere. where should it be attatched ? it only clicks when using the O/S indicator, no noise on N/S indicator. no lights either.

theres a big blue chunky thing in the loom in the boot, i think its the night dimming relay, which i dont have on mine, and ive heard nothing but bad things about them on here. whats the best thing to do with this ? at the moment hes not looking to spend much on it, as once he gets it to an MOT he might be told its scrap. but it would be nice to at least have brakes and indicators to get to the station.

headlights - we dont even know what the switch does relative to the lights. with the top of the switch 'in', is that all lights off, middle position sidelights, bottom end 'in' headlights ? only the headlights work, but flicking to high beam turns them off. one sidelight works, and the rear 'red' lights have a mind of their own with seemingly no pattern to when they choose to work, or how bright they are.  no bulbs in reverse lights, so not checked them.

[Rich_s]

Wiring is not too bad, straight forward enough on simple looms like on our cars, but then again i have made a few wiring looms for my motorbikes over the years when they have needed replacing.

First thing is to make sure the bulbs all work, easiest way is put them in a known working bulb holder, next thing i would do is check the earth side of all bulb holders is gegtting back to the battery earth, for this use your multimeter on the ohm scale, touch the 2 wires together and it should read zero, then put one wire/probe on the bulb holder earth and the other on the car body, somewhere bare metal, should then read 0.

if that is all ok turn the light on, turn the multimeter to read 20 volts, put live on the bulb live feed, earth wire on body and see if you get a reading, if nothing then try the switch and see if it is getting and sending power out, if so there is a break bewtween the switch and bulb, which is always interesting trying to find.

its just trial and error usually until you find the problem, i would offer to come and help but think you are a fair drive away from me.

good luck
rich

[James]

if you don't know how to use a multimeter then you're going to have issues.

generally wiring is very straight forward — it's rational and logical when it's in good condition and how it left the factory — the issue are previous owners who have hacked it apart not knowing what they are doing.

i'd rather do a bit of wiring (on a car that hasn't been messed with) than heavy and dirty mechanicals.

[Fizzy]

im sure learning to use the Mm cant take too long. and yes, one of the problems is that a lot of the wires were not connected when he got the car, they've been sprayed over so every wire seems to be red :o hasnt even got a full set of bulbs.

can you just concentrate one one thing, say the N/S sidelight, and keep fiddling till it works, or do other parts of the system have an effect on it (other than the switch) ? so for example if the rear light isnt working, will it effect if the headlights work properly ?

[andytr6]

indicator flasher on GT6 is behind dashboard - I s=till can't find mine but can hear it.  I intend to relace with solid state device like I did on the TR6 - which now works perfectly.  
I also had lots of earth probs on GT6 - as said its mostly earthing - check each bulb holder goes to earth.
Light switch up is off middle is side lights, down headlights as you said.

[rotoflex]

The only 2 settings on the MM you'll be using are:
continuity
12VDC

Show us a picture of the front of your MM so we can tell you which holes to plug the leads in, & what range to switch it to.

Do you have a link to an online wiring diagram for the car?

[Fizzy]

well we made a bit of progress, got rid of some duff bulbs, a duff brake light switch, some duff wiring. no power was even going to the rear lights. we found a live, tested things, ordered some bits that should be here today. but we got the rear red lights working, the brake lights work when i touch the wires together, so just need to fit the switch. the headlights work. one of the sidelights we cant get off. are there captive nuts behind them, because the screw wont come out, and you cant get to the back of them so i think i need to drill a hole in the valance behind the light.

also, exactly where is the flasher unit and what does it look like ? mine is cylindrical and easy to see, but however much we look just cant find it. does anybody know anything more accurate than 'behind the dash' ?

the brake light switch - the one that came out i didnt understand how it worked. the plunger went in towards the driver, yet the pedal goes away from the driver ? how does this work ?
cheers.

[GarthT]

yamaha_fizzy wrote:

the brake light switch - the one that came out i didnt understand how it worked. the plunger went in towards the driver, yet the pedal goes away from the driver ? how does this work ?
cheers.

when the switch is out, ie the brake pedal is not pressing it in, it makes contact, when it is depressed it breaks contact.

as James said, I'd rather mess on with electrics, (messed about by PO or not) than do dirty stuff. Maybe I'm soft.....

[JohnD]

Fizzy,
You expect something to happen when you press a switch or button.  But it is as possible to construct the switch so that it happens when you release it.  
Your brake lights are wired so that the normal state is for them to be switched on - only when the brake pedal is released do they turn off.

Or does that leave you more confused, or dare I say, fizzy?

John

[redzer]

The flasher unit on my 72 spitfire is a small silver cylinder and is loose in the wiring if you look up between the steering column and centre console,
having said that behind my dash is like a retirement home for those blue plastic clips and most wires seem to be replaced with red, blue or black wires so theres a reasonable chance thats not where its normally located  :)
Tony

[Fizzy]

i see what you mean, like you say, i just assumed that the button pushing in is what activates it. the bits should hopefully already be at my mates, im going round later to give him a hand, so hopefully it should all work out. so the contacts in the switch live 'in front' of the wire end contacts, and when you push the pedal from the switch, the little spring pushes the contacts back and into the wire ends ?

will hopefully have all lights working by the end of the day, weather permitting. except maybe the indicators, no idea what state the flasher is in, and still have to find it. niether of us are contortionists, so going headfirst into the footwell laying on the seat is hard work ;D

[ARH]

Think of wiring as being like plumbing. electricty will flow like water in pipes. the wires being pipes. switches will be like taps, stopping the flow. electricity will flow from positive to negitive. Most electrical problems on old cars are due to corrosion. Clean all connections as you find them. lights often have bad earth connections so clean all of them.

remember electicity is smoke, if you let the smoke out it will never work  :)

[Howard81]

My MKIV was very similar. The best method I found was to remove the entire loom from the car, clean every contact and replace all the wires that were broken.  Any dead wires were replaced and wrapped back up in the loom.

The worst were those blue scotchblock connectors, I removed about 20 of them! The car had 3 different radio looms spliced in everywhere! Joins were soldered and covered in shrinkwrap.

Putting it back in the car was simply a matter of following the wiring diagram. Easy.

[rotoflex]

Useful tools for cleaning connections:

Scotchbrite pad

Dremel tool with wire wheel (they make one wire brush that's about the size of a matchstick that's really useful)

[aar0sc]

Howard81 wrote:

The worst were those blue scotchblock connectors, I removed about 20 of them!

I keep finding them underneath my car  :-/