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Fuel Pump Electrics


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Hi All

 

So i'm kind of finishing off the installation of my new Autosparks harness on my 72 Pi.

 

Now call me dumb as i didn't think about it when orderring the harness, but its been suggested that the feed to the fuel pump should be a heavier gauge wire and possibly be fed via a relay, to make sure no or less current drop by the time it al reaches the pump and that the wiring does not overheat, or so i understand things.

 

So assuming that is right, has anyone else done it and can someone give me some info on how to do it, what gauge wire to use, what relay to use if thats sensible, and where to connect all that.

 

The harness is in and more or less finished but with no interior in the way now is the time to tackle this kind of thing.

 

For info i'll pretty much be running original Pi spec, so Lucas pump etc but in the future one never knows so flexibility would also be a fine idea.

 

Cheers

 

Keith

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I just ran an extra, fused, power feed from my additional fuse box to the back of the car.

I also ran a new earth/0v feed.

 

Then install a suitable, 30a, relay near the pump and use the original power feed to just power the relay.

 

I think i used 25a rated cable.

 

Hth

 

Steve

Edited by Steves_TR6
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Keith,

 

I took the existing output wire from the inertia switch to the coil connector on the relay (pin 85). Connecting the other coil (86) to earth on the car)

 

Cable there are lots of different ratings available for car wiring , thin wall, because of thinner insulation dissipates heat easier and the same size of conductor is rated higher than the better insulated pvc. To be honest you need less than four metres of cable and it's all about the same price, but if it snaps or overheats then your car will stop, so I used 35amp PVC for physical strength and electrical overkill.

 

Connecting between battery and the relay (pin30) with the wire and an inline fuse, and a further section between pin 87 to the pump. I then ran a black similar sized wire (another five metres) between the car earth circuit near the near side rear light cluster in the boot to the battery earth strap and on to the cars front earth loom near the headlights and ensured the pump earth connected directly to this.

 

 

Why the "complicated" earth - well I opened up my original loom and found that my car had three earth sections, rear lights terminating near NS light cluster, instruments terminating on a tab near cutch slave cylinder, and front lights, horns terminating on a tab in centre of front valance. The three sections were not interconnected and relied on the three tabs and good body conductivity for the negative return path. I just linked all three with the large earth in addition to the existing tabs and to the battery earth strap.

 

My car had the original horn relay, & overdrive relay and I fitted headlight and fuel pump relays, so I replaced all the relays with the same type of relay in order that I only need to carry one universal spare.

 

The total cost was about £25.

 

Alan

Edited by barkerwilliams
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I think you will find that Autosparks as a rule use an uprated cable for the fuel pump regardless (You could check with Paul their tech guy)

Stuart.

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The guy I spoke to at Autosparks said they automatically fit uprated wire for the pump supply in their harnesses. He also said that they do not recommend the use of a relay in the pump circuit so don't fit them as standard.

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The problem in not fitting a relay is that all the power is then switched by the ignition switch. Personally I would always fit relays to switch high powered items.(headlights, cooling fans, fuel pump etc) They do a better job and take the load of the 40+ year old and expensive to replace switch gear on the car.

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The problem in not fitting a relay is that all the power is then switched by the ignition switch. Personally I would always fit relays to switch high powered items.(headlights, cooling fans, fuel pump etc) They do a better job and take the load of the 40+ year old and expensive to replace switch gear on the car.

+1.

Did Autosparks explain why a separate relay for the fuel pump is not recommended?

I bought their harness with a relay.

Waldi

Edited by Waldi
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Hi All

 

Thansk for the replies.

 

In line with Stuarts comments i dropped Autosparks and e-mail over to ask, both about the gauge of the feed and realy so should get a reply fairly soon. They've always come back to me ok on the odd question i've asked. So i'll post an update as soon as i has a reply.

 

On a similar (electrical) but unconnected note whats the best way to test my "Highly Professional" installation? lol.

 

Do i just stick a battery on and see if the lights work, things like the fuel pump feed i guess i can check via a multimeter.

 

Car is not running or that close too but would like to check somethings are right before i finish everything and find out stuff does not work the hard way.

 

Cheers

 

Keith

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Do i just stick a battery on and see if the lights work, things like the fuel pump feed i guess i can check via a multimeter.

To test you could not connect the battery live cable and just lash up an inline fuse socket between the battery and the vehicle +ve connector cable so that you have some protection in place for the unfused items on the car. A 15 amp fuse would allow most items on the car to be tested one at a time.

 

Alan

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+1.

Did Autosparks explain why a separate relay for the fuel pump is not recommended?

I bought their harness with a relay.

Waldi

I cant remember Waldi TBH but I have to say that I wasn't completely satisfied that what the guy was telling me generally was very sound. I am a complete novice when it comes to electrics and I found him fairly unhelpful from an advice perspective

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Sean,

Autosparks are definitely far more knowledgeable than me,

But I disagree on this one.

A relay will give a higher voltage to the pump and reduce the load on the ignition switch. You can also fuse the relay separate which adds further protection.

 

For testing the new loom, the approach with a small fuse is good one.

I tested resistance first, the resistance of the brown wire to earth should be very(very) high, off course with all users switched off.

Switch on each circuit, one by one as a next step.

Waldi

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Hi all

 

A bit slow with my reply. Yep gonna go with the conect it all up with a smaller inline fuse, any problems that should blow the fuse first.

 

Also had a reply from Autosparks on the reply question.

 

Autosparks are way more knowledgeable than me as well, but i suppose they have to take care on giving "advice" due to liability issues.

 

Anyway i've found out the reason behind the no relay in your pump feed.

 

Its an unwritten "rule" esp in cometition that fuel pump feeds are unfused and non relay as if either fails you stop, not good. But if you are prepared to carry spares of both?

 

They've advised me that the harness's they supply would be copies of the Triumph specification, but that curiously, the Main harness uses a 14/0.30 cable, yet the rear harness uses a 28/0.30 cable and that this would have been recorded from an original harness set.

 

I asked them to specifically check my Quote/Sales number to check if my harness is of that spec and it would have been. So it seems the main bit can handle circa 9 amps and the rear 17amps and thats the way it was designed. Odd?

 

I may well go the fuses relay route and carry spare as it does not seem like a safety, ie explosion issue just a breakdown one, which can be bad enough.

 

Thanks

 

Keith

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If reliability of the fuel pump is of great importance, a relay will help to improve this, since it relieves the ignition switch.

The likelyhood of a relay failure is lower than the likelyhood of an ignition switch failure due to the much higher current of a Bosch pump in combination with the age of the switch. Cannot back this up by hard data, just my opinion.

Waldi

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If reliability of the fuel pump is of great importance, a relay will help to improve this, since it relieves the ignition switch.

The likelyhood of a relay failure is lower than the likelyhood of an ignition switch failure due to the much higher current of a Bosch pump in combination with the age of the switch. Cannot back this up by hard data, just my opinion.

Waldi

+1 Spot on Waldi.

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Hi All

 

Waldi, Kevo.

 

Kind of agree and in reality Autosparks concede the point that having a big current through a 40 plus year old ignitions switch is not ideal.

 

But i suppose they are supplying a re-manufactured Triumph design rather than a bespoke and guaranteed perfectly designed one or few off. Although i'm sure they would if asked and paid.

 

But i'll be looking very closly at the bigger direct feed with the ignition just switching a relay.

 

Cheers

 

Keith

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Hi All

 

Waldi, Kevo.

 

Kind of agree and in reality Autosparks concede the point that having a big current through a 40 plus year old ignitions switch is not ideal.

 

But i suppose they are supplying a re-manufactured Triumph design rather than a bespoke and guaranteed perfectly designed one or few off. Although i'm sure they would if asked and paid.

 

But i'll be looking very closly at the bigger direct feed with the ignition just switching a relay.

 

Cheers

 

Keith

Hi Keith

 

This is my wiring diagram of my 72 CP car, it may be of some use.

TR6 kg wiring Diagram.pdf

Edited by Kevo_6
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Hi Kev,

 

Great diagram. What did you use to create it. I would like to redraw mine to include all the changes I have made on mine ( many similar to yours).

 

Chris.

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Hi Kev,

 

Great diagram. What did you use to create it. I would like to redraw mine to include all the changes I have made on mine ( many similar to yours).

 

Chris.

Yes Kev,

Me Too.

Nice work.

Waldi

Hi Chris and Waldi

 

Thanks but can’t take all of the credit, I used the 70/71 drawing from here http://www.advanceautowire.com/tr2506.pdf as it was closer to a UK 72 cp car and I used Cute PDF editor which was free and still might be but I know they changed the software slightly.

I did this 4 to 5 years ago but basically deleted everything that wasn’t relative to my car and then added all the other bits. Very handy to have a laminated A3 copy on the wall in the workshop.

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Kev

 

Tried to open this the other day hoping it would give me a template for mine, esp given the comments about the 71 and 72 Advanceautowire PDFas as i found the same.

 

But i cannot open it.

 

Using Adobe Reader 9.1 and getting the msg "error processing a page"

 

Not be a particular teck wizard not idea how to resolve.

 

Cheers

 

Keith

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Thanks Kev,

 

Yes I thought it was based on the Advance Auto-wire diagram but nicely amended. I will look into some software to try and edit one of theirs to suit my mods. When doing the mods its easy to kid yourself that you will never forget what you did but 2 years down the line it doesn't make as much sense! the A3 laminated diagram is the way to go.

 

I originally viewed your diagram but now like some others cannot open the file and if I try and download my antivirus gets very excited.

 

Chris

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Thanks Kev,

 

Yes I thought it was based on the Advance Auto-wire diagram but nicely amended. I will look into some software to try and edit one of theirs to suit my mods. When doing the mods its easy to kid yourself that you will never forget what you did but 2 years down the line it doesn't make as much sense! the A3 laminated diagram is the way to go.

 

I originally viewed your diagram but now like some others cannot open the file and if I try and download my antivirus gets very excited.

 

Chris

Hi Chris

 

Not sure wat is at happening there, I know Keith’s son managed to open it with Nitro Pro 9 but maybe another different PDF reader or use a different web browser.

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