How do I read a wiring diagram?

esray

Member
Dear All,

When you look at a switch on a wiring diagram, does it show you the positions of the terminals as if they and the back of the switch were facing up to you from the page (i.e. with the actual switch facing away) or with the switch facing you and therefore the terminals on the back facing away from you, please?

Obviously this makes a big difference to what is left or right!

ATB Ray
 
I'd never rely on the wiring diagram representing the reality of what the switch looks like. Check the colour of the wires into the switch and map those to the connections on the wiring diagram.

Which switch are you referring to?

Bri.
 
Brian-Northampton said:
I'd never rely on the wiring diagram representing the reality of what the switch looks like. Check the colour of the wires into the switch and map those to the connections on the wiring diagram.

Which switch are you referring to?

Bri.

Hello Brian,

Thanks for replying.

The wiper motor switch. I've got slow speed but no fast. There are 6 terminals on the switch, and I have no idea which is the fast wipe, nor which colour wire is fast wipe?

Ray
 
Ray

On complex wiring diagrams the switch terminals will be annotated with a number or letter or combination of both. On simple diagrams the easiest way to tell which terminal is which is by the colour of wire coming off it. The orientation of the switch in the diagram will more than likely bear no relation whatsover to the actual orientation of the physical switch so the only way to be absolutely sure is to use a meter to check which contacts are open or closed with the switch in each of its positions. Once you've determined that and you know what the switch is designed to do then it's fairly straightforward to figure out which contact should connect to which supply, earth or component. Treat a wiring diagram as a functional representation of the circuit rather than a picture of how the circuit is implemented in practice. If you try to relate the orientation of the symbols in a diagram with the actual switch and how it is fitted you'll only get confused.

I hope that helps. I've been reading wiring diagrams and circuit diagrams for years so to me it's easy, but it's not the easiest thing to explain in writing. Much easier to show someone by leading them through a diagram.

Dave
 
Hello Brian, Dave,

I get that a wiring diagram is only a representation of the circuits, but what is the point of having separate diagrams for each model/year with numbered terminals and colour-coded wiring if none of it represents the actual circuit? I mean what is the point?....

I have followed the diagram as follows:

Dash Switch terminal number Wiper Motor plug-in terminal number

1 - Purple/Light Green 1 - Black Earth

2 - Blue/LG 2 - Red/Green

3 - Brown/LG (Appears to be permanent live) 3 - Blue/Green

4 - Brown/Purple 4 - Brown

5 - Yellow/LG 5 - Brown/Green

6 - Red/LG

All I appear to have is slow speed?

Ray
 
The point is, the diagram is MEANT to represent in schematic form exactly what is in your car. Although I can't comment specifically on your case, do bear in mind that your car is now around 40 years old, plenty of time for people to do all sorts of strange things to the wiring.
 
WarrenL said:
The point is, the diagram is MEANT to represent in schematic form exactly what is in your car. Although I can't comment specifically on your case, do bear in mind that your car is now around 40 years old, plenty of time for people to do all sorts of strange things to the wiring.

Hello Warren,

Thank you for your post.

I have eventually worked out the answer to my initial question; you read the diagram as if the front of the switch is facing you and therefore the terminals on the back are facing away from you (as of course they are in reality).

Turns out I have both the switch and the wiper motor connector/delay wired correctly, but the plastic box attached to the wiper motor (into which the connector plugs) contains switches that control the wiper park position etc is damaged and this also contains contacts that control the wiper speeds. I have ordered a replacement.

Best regards,

Ray
 
raylish said:
Hello Brian, Dave,

I get that a wiring diagram is only a representation of the circuits, but what is the point of having separate diagrams for each model/year with numbered terminals and colour-coded wiring if none of it represents the actual circuit? I mean what is the point?....

I have followed the diagram as follows:

Dash Switch terminal number Wiper Motor plug-in terminal number

1 - Purple/Light Green 1 - Black Earth
2 - Blue/LG 2 - Red/Green
3 - Brown/LG (Appears to be permanent live) 3 - Blue/Green
4 - Brown/Purple 4 - Brown
5 - Yellow/LG 5 - Brown/Green
6 - Red/LG

All I appear to have is slow speed?

Ray
Hi Ray.

I have just finished repairing the intermittent wipers on my car, (successfully :D ), and I have been studying the diagram recently, and unless your wiring is different to mine, (and the spare switch that I have), you have the wires on 3 and 4 on the dash switch swapped over :?

You seem to confirm this as you say the diagram replicates looking at the rear contacts from the front, but I am not sure that this is correct. The switches I have, have the numbers embossed on the back. and the order they are in, (starting from 1 and moving clockwise looking from the front of the switch), is...

1 - Purple/Light Green
2 - Blue/LG
4 - Brown/LG
3 - Brown/Purple
5 - Yellow/LG
6 - Red/LG

or anti-clockwise looking at the rear of the switch...

wiper_switch.jpg


Looking at the circuit diagram, the effect of reversing these two wires will indeed give you slow speed wipers, but no fast speed or delayed wipers, but as well as that I cannot see how, if wired the way you indicate, that you are not blowing fuses when the wipers are switched off, as there is a short between the +12V and ground connections, through the self parking switch.

You say you believe that this is where the fault lies, so I would be interested as to why you think that, (have you tested it with a multimeter), and I would be concerned that maybe it has had the contacts burnt out, due to this possible shorting, and the same will happen with a new one.

Another question would be, has the car always only had slow speed since your ownership, or was everything fine before the fault developed? If it has always been this way then I would definitely re-check the wiring before changing the parking switch/connector assembly.

I have a 1972 3500S vehicle, so maybe your car is a different model with a different switch, so I could of course be completely wrong :shock: :shock: :shock:
 
raylish said:
I have eventually worked out the answer to my initial question; you read the diagram as if the front of the switch is facing you and therefore the terminals on the back are facing away from you (as of course they are in reality).

I didn't want to confuse the issue but that is simply not the case. If it appears to be then it is merely a coincidence. You can never hope to hold up a wiring diagram, align the switch on the diagram with the switch in the car and expect it to look the same. I can pick up a wiring diagram and do the vast majority of circuit analysis without going anywhere near the car. As I've said previously, the only way to accurately interpret how the wiring diagram has been physically implemented on the car is to look at the colours of the wires and the terminal indentification markings on the component that those wires are attached to. Notwithstanding errors on the wiring diagram (and I've seen them before .....and yes that's a real pain when fault-finding), if the diagram is correct for the year and model of car and the wiring in the car does not match then something is wrong or something has been altered in the 40 or so years since the car came off the production line. That's why it's important that the diagram you have for your car is amended whenever you modify the wiring. It's the only way to keep tabs on what's been done.

Dave
 
Hello Dave & Phil,

Thank you both for your repeated and patient attempts to assist me!

I did as Dave suggested and traced the wiring colours from the switch to their respective outcomes. This (as Phil has so clearly pointed out) led me to wire the switch exactly as Phil outlines in his post. My previous wiring did indeed blow fuses (and lots of 'em!).

As a result I am delighted to have intermittent and fast BUT NOW NO SLOW!

Still at least I do now have wipers and my fuse consumption has fallen dramatically :) :!:

Phil - The photo you took really is clear and excellent - You should consider pinning it somewhere in the forum as a guide to idiots like me who need a picture instead of a diagram :!: :!:

My best regards to you both,

Ray
 
raylish said:
Hello Dave & Phil,

Thank you both for your repeated and patient attempts to assist me!

I did as Dave suggested and traced the wiring colours from the switch to their respective outcomes. This (as Phil has so clearly pointed out) led me to wire the switch exactly as Phil outlines in his post. My previous wiring did indeed blow fuses (and lots of 'em!).

As a result I am delighted to have intermittent and fast BUT NOW NO SLOW!

Still at least I do now have wipers and my fuse consumption has fallen dramatically :) :!:

My best regards to you both,

Ray
Hi Ray.

Glad you're almost there.

Since you did have slow to start with, it is a bit of a mystery :?

As the delayed wipers work however, it narrows the possibilities to the wiper switch connection 4, (Brown/Light Green), not being connected properly. This goes from the wiper switch to the delay governor switch, and on to the motor.

Since delay works OK the connection between governor and motor must be good, so check with a meter that the wire from the wiper switch connection 4 does indeed connect to the wiper motor connection 5, and check that on the wiper switch connection 4 you get +12V when switched to slow wipers.

I'm guessing that the parking feature doesn't work either, if you switch off the wipers mid-sweep, as this also uses connection 4 to supply power to the motor.

Could be simply dirty contacts on the wiper switch :shock:

I did a write up of my wiper overhaul and added circuit diagrams showing the power routes for all speeds which may help you.

Wiper Overhaul

Good luck :D
 
codekiddie said:
raylish said:
Hello Dave & Phil,

Thank you both for your repeated and patient attempts to assist me!

I did as Dave suggested and traced the wiring colours from the switch to their respective outcomes. This (as Phil has so clearly pointed out) led me to wire the switch exactly as Phil outlines in his post. My previous wiring did indeed blow fuses (and lots of 'em!).

As a result I am delighted to have intermittent and fast BUT NOW NO SLOW!

Still at least I do now have wipers and my fuse consumption has fallen dramatically :) :!:

My best regards to you both,

Ray
Hi Ray.

Glad you're almost there.

Since you did have slow to start with, it is a bit of a mystery :?

As the delayed wipers work however, it narrows the possibilities to the wiper switch connection 4, (Brown/Light Green), not being connected properly. This goes from the wiper switch to the delay governor switch, and on to the motor.

Since delay works OK the connection between governor and motor must be good, so check with a meter that the wire from the wiper switch connection 4 does indeed connect to the wiper motor connection 5, and check that on the wiper switch connection 4 you get +12V when switched to slow wipers.

I'm guessing that the parking feature doesn't work either, if you switch off the wipers mid-sweep, as this also uses connection 4 to supply power to the motor.

Could be simply dirty contacts on the wiper switch :shock:

I did a write up of my wiper overhaul and added circuit diagrams showing the power routes for all speeds which may help you.

Wiper Overhaul

Good luck :D

Phil, Dave,

In the end (and mostly due to the efforts of you two) I realised that I was the victim of my own stupidity and poor memory!

Way back when I swapped a back-lit perspex switch panel from my 2000 TC donor car into my 2000 body with 2200 SC engine main car, I found that I had to use the TC wiper switch (in place of my existing 2000 SC switch) or the green pointer switch did not 'point' correctly?

Unbeknown to me, the switch must have been very slightly different and this was why I was wiring it incorrectly. I have now put back the original switch (pointing incorrectly), wired it up as per Phil's instructions and everything works.....Well, the delay wipes and then freezes before it is due to return to park....But I have fast and slow speed wiping and the blades park correctly :D

Ray
 
Glad you've managed to sort it Ray.

raylish said:
the delay wipes and then freezes before it is due to return to park

This can be a symptom of the delay unit returning too quickly. I discovered this when I was sorting the delay on my 72 3500S. The plunger in the delay unit was returning before the wiper motor had a chance to cycle back to park. I surmised that the plunger returning too quickly was removing the supply to the motor and causing the wipers to stop mid-sweep. I put a thicker piece of sponge in the delay unit and that fixed it. It might've just been luck rather than judgement though :LOL:

Dave
 
raylish said:
Phil, Dave,

In the end (and mostly due to the efforts of you two) I realised that I was the victim of my own stupidity and poor memory!

Way back when I swapped a back-lit perspex switch panel from my 2000 TC donor car into my 2000 body with 2200 SC engine main car, I found that I had to use the TC wiper switch (in place of my existing 2000 SC switch) or the green pointer switch did not 'point' correctly?

Unbeknown to me, the switch must have been very slightly different and this was why I was wiring it incorrectly. I have now put back the original switch (pointing incorrectly), wired it up as per Phil's instructions and everything works.....Well, the delay wipes and then freezes before it is due to return to park....But I have fast and slow speed wiping and the blades park correctly :D

Ray
If the wipers park normally on slow and fast speed, then I concur with Dave that the most likely culprit is the delay governor switch, but it must be stuck midway somehow, as if the plunger were to return fully it would supply power to the motor, and the wipers would just continue to run.

Remove the governor switch, clean thoroughly and as Dave says check that the sponge is there :shock: and lubricate the shaft of the plunger before reassembly.

Once reassembled, put your finger over the end where the vacuum pipe goes, and press the plunger in. Hopefully it will return slowly. Letting more and more air in by moving your finger off the end will cause the shaft to return quicker. Also check with a meter that the contacts are switching over correctly.
 
If the wipers park normally on slow and fast speed, then I concur with Dave that the most likely culprit is the delay governor switch, but it must be stuck midway somehow, as if the plunger were to return fully it would supply power to the motor, and the wipers would just continue to run.

Remove the governor switch, clean thoroughly and as Dave says check that the sponge is there :shock: and lubricate the shaft of the plunger before reassembly.

Once reassembled, put your finger over the end where the vacuum pipe goes, and press the plunger in. Hopefully it will return slowly. Letting more and more air in by moving your finger off the end will cause the shaft to return quicker. Also check with a meter that the contacts are switching over correctly.[/quote]

Dave, Phil,

Thank you both very much for all your time and knowledge - I do appreciate that you both have cars similar to mine that place substantial demands on your SPARE time and attention!

I shall do exactly as you say :!: :!:

I should add that thanks to your ongoing advice, Roy is running absolutely beautifully now and I think that it is these (sometimes too few) occasions when everything goes just right with a Rover that make all the effort involved worthwhile :D
 
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