Electrical: glow plug wiring for numpties.

[dean36014]

First off, i'm a complete numpty with wiring, struggle to deciper wiring diagrams in haynes manuals. My daily, a Citroen BX 17rd has an occasional fault where the glow plugs fail to work. I've a sneaky feeling its something to do with the ignition switch if that's possible, I've cleaned connections etc and not found any faults. My question is can I wire up a back up heat button and still leave the original system in place, i.e just to be used when the original system plays up. Is it as simple as using a relay to fire a feed to the original feed to the first glowplug or will that cause problems with the existing wiring?

[3VOM]

If it is the ignition switch then you should be able to bypass the glowplug part of the ignition switch function. However, making a complete secondary glowplug circuit would be a massive task. Glowplugs draw tons of current and the wiring would need to be seriously large, carefully planned and use FO sized relays not your normal 12v 30amp things. I'd think fixing the existing, although problematic and tedious would be a better and safer option.

[Talbot]

The glowplug controller on these (Blue-topped box the size of a fag packet) is generally very reliable, but they do suffer from corrosion of the multi-plug that connects to it.  There's a heavy battery lead to it, and the feed to the plugs, and then the multi-plug which (IIRC) has the 0vDC connection, ignition switched live, a connection to the coolant temperature and a feed to the dashboad lamp (as the dashboard lamp is timed based on the engine coolant temperature)

 

Check the multiplug.  I'd go so far as to say remove the unit, clean up the connections and maybe put a new multi-connector on the cables (same design as a relay multi-way connector)  The rest of the system is very reliable, as noted by the fact that I have about 7 glowplug relay/controller units stashed away and have *never* actually changed one.

[vaughant]

As above probably better to fix the existing system as it keeps it all sweet then but as a back up the easiest way to do it is to run a switched line feed to the coil of the relay, that way round you're still sticking to the original manufacturer's glowplug system but energising or activating it from a different source.

 

It should be really easy to fault find the old system though, most likely a poor connection somewhere.

 

Not sure if you're that much of an electrophobe to know how a relay works but a quick description is that it acts as an electrically operated switch, the contracts are a lot beefier inside than a simple throw switch and cause a lot less flash across as it closes meaning you can run much higher currents through it.

 

The coil can be activated from a much lower current hence a thinner cable can be run to the relay coil itself to energise it.

[Honey Badger]

Quick explanation on relay function from Ave on Youtube

 

 

doesn't help with the problem but explains the relay function.

[Guest Hooli]

If you think the fault is the ignition switch then if you put 12v to the switched live (from the ignition switch) on the glowplug controller that should warm the plugs up as a test. If it works a new switched live & dash switch would bypass the ignition switch until you sort it.

[dean36014]

Testing is awkward as it works perfectly for weeks on end then normally at around 2am when I've finished work and want to go home and sleep it plays up! I'll have another look at the blue box and clean up the plug. My glowplug light doesn't work (dashboard clocks fault I think)  so can only tell if its work if i hear the heater fans slow fractionally! I have a new set of clocks to fit so hopefully all my warning lights might start working then as presently oil, temperature and glow plug lights are dead even after fitting new bulbs. Grounding the sensor wires doesn't bring them on either so I'm assuming its a clocks fault.

[MikeR]

is the engine temp sensor ok ( may not be the same sensor for the gauge)   if the system thinks the engine is warm/hot , it might not switch in the glo plugs as it will be thinking they are not needed ......

[Stixy]

Yes you can   but have it through a big relay on a push button switch so only on when its pressed 

[mat_the_cat]

There's no engine temperature sensor for the BX glowplug system - that came in with the Xantia.

[paulplom]

A friend of mine had a fiat scudo 1.9d. His glow plugs stopped and a mechanic over the road wired them so they came on with his high beam. He used to sit there at 6.00am with his lights on full beam shining in the neighbours windows opposite before it would start.

There was also something wrong with the heater too. He had to put 2 x 2 litre pop bottles of hot water on the dashboard to keep the windscreen demisted.

He was T boned in it when a young lass pulled out in front of him in a 60 limit. No one was hurt but she did him a favour in the end I think.

[twosmoke300]

Some of the wiring bodges I've seen must take longer and cost more than fixing the original problem . My ex brookjm Landy had been looked after by a "specialist " and the wiring was shocking - scotchloks every where and indicators etc all stayed live when key off ! I'm guessing that's why it had a battery isolator fitted .

Root cause was a wire rubbed where it went through the bulkhead . An hours work to fix and about 3 to unravel the rays nest repairs

[Guest Hooli]

Odd that. Most electrical repairs I've done on older cars have started off by removing a rat's nest of extra wires & 9 times out of the 10 the original wiring works fine. Why do people do it?

[dean36014]

Well typically it started fine again this morning. Might just make up a heavy duty cable to bridge from the battery to the glow plug relay so next time it plays up I can quickly test for problems. I'm assuming that if the plugs then work it will point to a fault with the switching side of the electrical circuit. At the moment I'm tied up trying to get the other BX ready for its jaunt to France at xmas so no time to start playing big time with this one. Always have the van to fall back on if it fails to start at home.

[Guest Hooli]

Which is wot I said ages ago...

 

No one listens in this place

[twosmoke300]

* awaits tale of "repair" with speaker wire and chewing gum wrapper

[Guest Hooli]

Feeling cynical today?

[dean36014]

Nope no speaker wire here, I try and repair things properly. It's just hard to find an intermittent fault when it only seems to do it in the early hours of the morning. I've made a cable up out of a cheap and nasty jump leas for emergency purposes and to help pin point the fault. Guaranteed now it won't do it again for months.

[twosmoke300]

Feeling cynical today?

No wonder really

[Guest Hooli]

No wonder really

I agree tbh, it worries me what some people do to 'fix' stuff.

[Guest Hooli]

Nope no speaker wire here, I try and repair things properly. It's just hard to find an intermittent fault when it only seems to do it in the early hours of the morning. I've made a cable up out of a cheap and nasty jump leas for emergency purposes and to help pin point the fault. Guaranteed now it won't do it again for months.

 

Take normal bit of thin wire too.

 

On the glowplug control unit try 12v direct to the terminal fed off the ignition switch. If they work then you've proved it's the ignition switch at fault.

[MikeR]

instead of poking a big bit of wire with lots of arc inducing amps somewhere under a dark bonnet on a wet and windy morning whilst in a rush muttering bugger bugger bugger   ....... arrange 2 wired in points that you can just clamp together   or a pre  installed piece of wire that will reach the battery terminal  ?  

[Talbot]

There's no engine temperature sensor for the BX glowplug system - that came in with the Xantia.

Are you sure? Even my Horizon Diesel used to know the engine coolant temperature and adjust the timing of the dash lamp acccordingly. That said, the BX may have suffered a cost-down on that, as the Horizon was the first car to have the XUD, so bits of the system may have been found to be over-engineered.

[twosmoke300]

The time is done through the changing resistance of the plugs as they warm up on older stuff

[mat_the_cat]

Are you sure? Even my Horizon Diesel used to know the engine coolant temperature and adjust the timing of the dash lamp acccordingly. That said, the BX may have suffered a cost-down on that, as the Horizon was the first car to have the XUD, so bits of the system may have been found to be over-engineered.

 

Yes - although there may be an ambient temperature measurement within the relay, as I've never actually opened one up. The Xantia had both a coolant temperature sensor and a throttle position switch, but I believe they were more to do with the time they remained on after starting than altering the initial glow time.