Electrical Switches etc.

chodjinn · Post by **chodjinn** » Wed Jan 30, 2008 10:52 am

I'm just finishing my new centre console out of fibreglass, and I've got a nice carbon fibre switch panel to use. I've figured out what i need in terms of numbers of switches etc, but i need a bit of advice in terms of wiring - and I am crap at this lol!!!

I'd also like to have individual fuses for stuff like the fuels pumps, water pump and fan to take the strain off the crappy (i.e. basic) MGB fuese box (which has 4 fuses!).

Basically I'd like to know if this lot will work:

1). Two fuel pumps; run from the ECU (split line) and using relays; what I would like are two 'kill' switches or toggle switches to use on the panel. the idea is that i can turn the ignition switch on for power, then flick both switches to start/prime the pumps before starting the engine; they'd also act as kill switches in the event of a crash etc.

Could I run in-line fuses, one for each pump? What amp should they be? If not, what/how?

2) Manual switch for the water pump (EWP Davies Craig thing). Not using any thermostat or anything, just a power line to the pump and an 'on' switch. Idea is that i start the engine, let it warm up, then flick on the water pump.

3) Manual switch for the fan; same idea as above.

For all four of the switches above, I'd like a small light to indicate when they are 'on'. I've found loads of little lights to use, but do I need a specific amp/voltage, and how would i wire them into the circuit?

that's it for now . . . thanks in advance!

chodjinn · Post by **chodjinn** » Wed Jan 30, 2008 11:51 am

I had half hour at work and came up with this;

http://www.the12volt.com/installbay/for ... 82658&PN=1

scroll down a bit for the diagram - can I use this set up and all four of the things mentioned above (Feul Pump x2, Fan, Water Pump)?

If so, how would I fuse them all, in-line from the 12v source?

thanks

Ian Anderson · Post by **Ian Anderson** » Wed Jan 30, 2008 12:47 pm

see
http://www.s-v-c.co.uk/about.html

Great company to deal with and good delivery /support

They have looms, relays for fans already wired etc

They also have switches with LED in the end to confirm circuits are on!

Ian

I have no relationship with SVC other than a very happy customer.

chodjinn · Post by **chodjinn** » Wed Jan 30, 2008 1:17 pm

Thanks Ian I've been hunting for a decent site like that for all the bits.

After spending lunch googling like amd I've found a bunch of diagrams to aid me wire in the switches/lights - all with automotive relays.

Still trying to figure out if i can botch two different MGB looms together to reduce the number of switches i need lol

ChrisJC · Post by **ChrisJC** » Wed Jan 30, 2008 1:24 pm

chodjinn wrote:
2) Manual switch for the water pump (EWP Davies Craig thing). Not using any thermostat or anything, just a power line to the pump and an 'on' switch. Idea is that i start the engine, let it warm up, then flick on the water pump.

I'd be careful about doing this - I would be very wary about having an engine running without having the water pump on! I imagine that the water would boil very quickly around the cylinders and in the head, but the temp sensor in the manifold would still be cold......

The circuit shown will work just fine. However, I would improve it if it were me. The problem is that the LED will come on irrespective of whether the relay is working (or even fitted!). I would take the +ve signal from the pump and feed that into the 470ohm resistor. That way the light only comes on if there is power actually on the pump. If you put a fuse between the relay and pump, then it will also tell you if the fuse has blown!

Just get an in-line fuse rated a tad higher than the pumps rating.

Chris.

jrv8 · Post by **jrv8** » Wed Jan 30, 2008 1:27 pm

chodjinn wrote:I had half hour at work and came up with this;

http://www.the12volt.com/installbay/for ... 82658&PN=1

scroll down a bit for the diagram - can I use this set up and all four of the things mentioned above (Feul Pump x2, Fan, Water Pump)?

If so, how would I fuse them all, in-line from the 12v source?

thanks

That's not really the way to do it, as the relay in your diagram is not working as it should. It's using the same fused power source as the switch.
You need to disconnect the strap between 30 on the relay and the switch, and replace it with a seperate fused 12v feed on pin 30.
This will protect the contacts of the switch, and allow you to fuse up the relay secondary +12v source to whatever you need. Don't forget to use the correct rating of wire for the secondary source.
Regards
Jim

chodjinn · Post by **chodjinn** » Wed Jan 30, 2008 3:03 pm

I really appreciate your help guys but that's just made me even more confused

I really am struggling to understand any of this at all. I really need this explaining in laymans terms!

Jim: Do you mean break the connection between pin 30 on the relay and the switch, then add in a completely separate 12V source (FUSED) to pin 30; but what do you mean by the last bit - "fuse up the relay secondary +12v source to whatever you need"???

Chris: In that diagram, what is the +ve pump signal?

I can't do both of the above though, as doing what Chris says means I can't get in a 2nd 12v source?!?

Basically the plan was to remove the crappy MG 4-way fuse box as there are multiple feeds to single fuses, and get a nice big fuse box and fuse everything separately. I don't really have any issues doing that I think because all it will be is ensuring the correct fuses are used for the correct bits of wire??

What is doing my head in is adding in the fuel pumps etc. as mentioned above into the above fuse box. I have no idea of the fuse/amp/volt ratins or whatever (see, i don't even know what is what!) the fuel pumps are or the fans/water pump

I wish I had never even bothered with this rewire!

Post by **katanaman** » Wed Jan 30, 2008 3:50 pm

I can send you the wiring diagram I drew up for my Scim if you want? It wont be exactly as you want but will be close enough and you can add or subtract as you need. For example I don't have two fuel pumps but one is there so you just need to double it up type of thing.

chodjinn · Post by **chodjinn** » Wed Jan 30, 2008 3:53 pm

Yes please Marki!

ollyhayter@hotmail.com

The problem is the original swiring loom has been chopped and botched by the previous owner so much i can't even identify what 'year' it is, even using a Haynes! I have also removed a few things like the radio, heated rear screen etc., but noticed he never had things like the fog lights wired up properly. Add to that all my additional bits and bobs; it's killing me!

Ian Anderson · Post by **Ian Anderson** » Wed Jan 30, 2008 3:59 pm

They (those more in the know than I) suggest that the Lucas switches are good for about 15amps - after that they tend to let the smoke out and it is difficult to get the smoke refilled!

So for the switches to work reasonably you need to limit to about half of the recommended or their lifespan will be reduced.

The switches with inbuilt LED lights in the stalks will mean you do not have to add other warning lights

They also do a rather nice relay unit in the others section where it can switch up to 30 amps and be fused accordingly with a blade type fuse.

On the water pump I agree it should be running as soon as the engine is - I believe they do a controller that will vary the speed of the pump dependant on temperature but then that is another thing to potentially go wrong and mean an expensive repair.

Something else to check is what wour full load current will be - fans, 2 fuel pumps, EWP, lights etc and you may be drawing more than the alternator can refill!

One last thing to look at in the wiring is presumably the key switch is used to activate all the circuits - and now that there is extra load could easily be overloaded (They actually can get very hot!) and may also need to be a relay activating unit.

Ian

ChrisJC · Post by **ChrisJC** » Wed Jan 30, 2008 4:00 pm

Does this help:

Jim did raise a good point - the relay was completely pointless in the original drawing!!

Chris.

Post by **katanaman** » Wed Jan 30, 2008 5:28 pm

will get it to you in a couple of hours when I get home.

jrv8 · Post by **jrv8** » Wed Jan 30, 2008 7:59 pm

[
Jim: Do you mean break the connection between pin 30 on the relay and the switch, then add in a completely separate 12V source (FUSED) to pin 30; but what do you mean by the last bit - "fuse up the relay secondary +12v source to whatever you need"???

Hi,

Yes, that's how it should be done. The contacts of the relay should have their own +12v supply. The idea is that the coil side of the relay draws low current , and so can be "switched on" by the switch without fear of damaging the contacts. The output side of the relay has heavy duty contacts and can switch the loads drawn by a fan or pump.
To do this, you will need a seperate +12v supply on pin 30, suitably fused with a line fuse.
If you read the rating plate on the fan it should give you the power in watts. Divide this figure by 12 to get the current that it will draw, and fuse the supply to the relay with a fuse of slightly higher value that that.
Jim

jrv8 · Post by **jrv8** » Wed Jan 30, 2008 8:08 pm

Chris,

The fuse connected to the pin 30 should not take its power from the input side of the switch, as this will be fused at a fairly low rating in the fusebox. Ideally it should be taken directly from the ignition switch controlled supply.

Jim

ChrisJC · Post by **ChrisJC** » Wed Jan 30, 2008 8:25 pm

jrv8 wrote:Chris,

The fuse connected to the pin 30 should not take its power from the input side of the switch, as this will be fused at a fairly low rating in the fusebox. Ideally it should be taken directly from the ignition switch controlled supply.

Jim

True, that was a bit of laziness on my part. I wasn't sure where to stop drawing! I didn't really want to go back to the battery / alternator.

Chris.

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