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BrianC

I've a strange issue with my 1988 1.6 gti. 

 

Initially the car wasn't starting, swapped out the tachymetric relay (fuel pump relay) with one from my 1.9 gti and it fired up straight away. 

 

But now it seems I've an electrical issue. The fuel pump seem to be surging electrically with the car started or even just the ignition on, buzzing noise from the pump and relay. 

 

Also the headlights seem to be on permanently on the dash and physically but this doesn't happen with the old faulty relay in. 

 

Not sure if it's all linked but I've ordered a new relay and pump as no harm replacing both. Is there anything else that could be causing this? Bad earth maybe? The car was just recently fully stripped for an underneath restoration and also for a full glass out respray. 

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PhilNW

Sounds like it might be the relay, possibly stuck in the "on" position. 

 

What do you mean by "surging electrically"

 

What happens if you supply a direct feed to the pump?

 

Any other systems being switched on as well as the headlights? 

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BrianC
1 hour ago, PhilNW said:

Sounds like it might be the relay, possibly stuck in the "on" position. 

 

What do you mean by "surging electrically"

 

What happens if you supply a direct feed to the pump?

 

Any other systems being switched on as well as the headlights? 

Basically every 3 or 4 seconds it's like the pump is priming, and the headlights go from dim (less voltage) to full brightness (more voltage) at the same time as the pump seem to being supplied with more voltage. 

 

No I didn't supply a direct supply across the pump, I'll give that a go now shortly, just hoping the new relay and pump will solve it but the lights issue has me skeptical, couldn't find any info linking the fuel pump relay to the lights, just the ignition system. 

 

Nothing that I can see is switched on anyway, but again unless it shows on the dash as switched on or it's obvious without a multimeter I didn't check any further. 

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PhilNW

Sounds like the pump and headlights have cross connected maybe due to missing or broken earth. Suggest get hold of a digital multimeter and check voltages and resistances to earth

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BrianC
On 6/7/2021 at 9:32 AM, PhilNW said:

Sounds like the pump and headlights have cross connected maybe due to missing or broken earth. Suggest get hold of a digital multimeter and check voltages and resistances to earth

Sounds like your right anyway, hadn't much time to check various things but basically the fuel pump is receiving power when I turn the lights on via the stalk with no key even in the ignition. 

 

Earth's seems good at the headlights, very little resistance back to negative. 

 

Didn't have time to test the rear earth on the passenger side rear light but when I unplug that earth the fuel pump stops receiving power, so looks like its crossed somewhere with the lights supply. 

 

I'll have to dig a bit further the weekend when I get some time 

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PhilNW

Another question to be thinking about is does the pump kick in when ?   with side light/dip beams/full beams/ when flashed?

 

The tachy relay and the lights switch have permanent feeds from the battery. just a thought as it happens with no key.

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