Glow plug circuit

[Guest Leonard Hatred]

 

My Golf has glow plugs wired to a switch and relay by the previous owner, it has a fuse mounted in-line and it keeps blowing. My question is - can the fuse be binned altogether?

I touched the glowplug wire against the battery for 15 seconds and they're definitely working, the car started readily after.

[dollywobbler]

I'd be wondering why the fuse keeps blowing myself. Something must be amiss. What rating is the fuse? I blew several fuses the other day after getting the wires mixed up on the relay...

[Timewaster]

Fuses dont just "blow". What size fuse is it?

 

I remember a customer returning some "faulty" fuses. apparently they blow!

[Pillock]

Get a multimeter and set it to read current. Put your glowplug wire onto one side of the meter and then put the other side of the meter to battery live - the meter will tell you how much current the glowplugs draw when they're heating. If this is more than the fuse rating, it will blow, but if it's LOTS more than the fuse rating there might be a problem somewhere.

 

The worry is if you're drawing mega-current, and you bin the fuse then the next weakest link is the wiring. If that goes up you've got a fire risk.

[scruff]

What Pillock says is good advice. You'll need a big fuse - I'd have thought each plug will draw between 7 and 13 amps each. Have you got a Haynes with a wiring diagram?

[Guest Leonard Hatred]

I've given up on Haynes, it makes much more sense when I bluster into doing jobs on cars instead of reading TFM.

 

As I said, it's not a factory setup, it's just an aftermarket switch married to some aftermarket wiring, aftermarket fuse holder and aftermarket relay as the factory system binned itself.

 

IIRC I put a 30amp fuse in the holder, then some tin foil. Both blew. I really need to buy a multimeter...

Will the relay absorb the current?

[Mr_Bo11ox]

which circuit is fused - the switch side of the relay or the glowplugs side?

[scruff]

Agree on Haynes but it might give you a clue to fuseage sizeage and where it should be etc

[scaryoldcortina]

Glow plugs typically draw about 6 - 8 amps each, you have 4... a 30 amp fuse might be marginal, but a 40 should cope. If it doesn't (and this is fairly likely) then the use of a switch rather than a timed relay may have made one of the glowplugs melt and short out internally, this will increase the load rather a lot. Get a multimeter and check the resistance of each glowplug or replace all 4.

[Guest Leonard Hatred]

which circuit is fused - the switch side of the relay or the glowplugs side?

 

Glowplugs side

[Pillock]

I'm a bit of a wuss with electrics and would probably have fused both sides of the circuit, switch and glowplug, but that's just me.

I must admit my bum clenches a bit when you describe putting tinfoil in an electrical circuit in place of a fuse. Just get a multimeter - Maplin do one for about a tenner - and check it properly. Remember to check the wiring and relay is rated higher than the fuse too, otherwise the fuse is not the weak link that it's designed to be and instead your wiring will "blow". Off the top of my head, a lot of common car relays are rated for 40A max so there's no point putting a higher rated fuse in, again your relay becomes the weak point.

[Guest Leonard Hatred]

I don't mind frying the relay. I think my question now is - can I use the relay as the fuse?

[M'coli]

I wouldn't trust it - it wouldn't be the first time that a relay's contacts have melted themselves permanently shut.

[Pillock]

No, relays are relays and fuses are fuses.

 

The danger is, without a fuse and your plugs pulling close on 40A as calculated above, you risk the relay overheating..... relays being mostly plastic, they'll burn nicely if you get them hot enough and so will anything else flammable around them.

[Guest Leonard Hatred]

I'll try a 40A fuse tomorrow...

[shite_meister]

I wonder if it was fitted because the previous owner baulked at the cost of a new genuine glow plug control relay? there might be cheaper alternatives from the likes of Durite, I can have a look ig you want in a book at work.

[Albert Ross]

There are different glow plug voltages available. Is the feed/output of the relay written anywhere on it? Can you read the info on one of the plugs to make sure they are matched? See Corsa A or B 1.5 for evidence of mismatched glow plug and relay voltages. Also Astra 1.7 Isuzu motors.