Glow plug relay not controlled properly - non-starter

[eightball]

Hey all, I have a 2.5td 4x4 1996 SGL5 Bongo that after a long wet trip to the south-west has returned a non-starter. As it turns over fine but doesn't catch my first thought was glow plugs somewhere. I initially thought it was the glow plug relay as I could measure battery voltage (12.8V) on the large pin in and nothing on the large pin out to the glow plugs even though I could measure voltage (11.3V) on the small controller pin in when I turned the ignition. So I replaced the relay only to discover it is not the relay. If I manually apply battery voltage to the small controller pins the relay opens fines. In fact if I do this I can start the van too so the glow plugs themselves are for sure ok.

So I am left now thinking that there is a problem with the switching of the relay and that the 11.3V I was measuring on the thin pins (fed by black and purple cables) is too low and there is somehow a problem with this circuit (doesn't seem to be continuous either when I test resistance).

Could someone please explain to me how the relay switching is controlled (to switch the relay on when engine is cold etc) and where I can go looking for or how to diagnose faults in the circuit that controls the relay (i.e. where do the thin purple and black cables that feed the small pins and are responsive to the ignition key) come from and go to????

Thanks
Rich

[eightball]

Further tests have confirmed its an earthing problem for the small black wire (connected to small relay pin) - if I directly earth the pin directly everything now works as normal. So if I turn ignition I see 11.2V or so across the purple/manual earth and relay on, after ~10 secs the relay clicks off and goes to 0V unless I actually start the engine - in which case the circuit stays on for while (I presume until engine reaches normalk opertating temp but I've not left it long enough to check it correctly swtiches off later yet).

So could someone please tell me where that thin black cable runs to earth? I can't figure it out from the wiring diagrams......

Cheers,
Rich

[eightball]

If I start the engine (by earthing the relay pin normally connected to the thin black cable) directly to the battery negative - it starts fine (so glow plugs heating) but I still measure voltage across the purple/black cables after a min or tow - shouldnt it start swtiching on and off to stop the glow plugs burning out - until the correct engine temp is reached?

[g8dhe]

See my answer in the PM, the earth for the relay is back on the passenger side of the engine! See diagram below earth point 16, lower middle of the diagram.

[eightball]

I may have found the loose earth wire for my relay - a free floating black cable coming from central (bulk head loom) that has obviously deattached from earth point 16.

Can anyone tell me what earth point 16 looks like and where it is exactly? I don't quite understand the figure Geoff posted above (although it enabled me to at least find the black loose earth wire!)

Thanks
Rich

[Northern Bongolow]

the standard earth points for most electrical items look like a little buzz bar with several white plastic connections to the buzz bar similar to this link, but each connection is made separately. similar to the link below.
https://www.google.co.uk/url?sa=i&rct=j ... 3673866261.

does this help any.
http://lushprojects.com/bongopartsmk2/c ... no=.html#6

[rita]

I may have found the loose earth wire for my relay - a free floating black cable coming from central (bulk head loom) that has obviously deattached from earth point 16.

Can anyone tell me what earth point 16 looks like and where it is exactly? I don't quite understand the figure Geoff posted above (although it enabled me to at least find the black loose earth wire!)

Thanks
Rich

Earth point 16 is at the very bottom of the drawing, look at the side of the engine and you will see a large steel plate with the earth points fix to it.

[eightball]

thanks - going back out to look - left or right side of the engine for the steel plate?

[Northern Bongolow]

drivers side. you cannot miss it. high up near the rocker cover.

[eightball]

thanks all, problem solved - found somewhere to bolt it to. It seems to fit well close to 4 (ATF dipstick on the upper photo here http://mazdabongo.wikispaces.com/Parts. In fact you can see the cable in the picture even - looping down between 2 and 4. Looks like its connected where I connected it - to a bolt with a small sheet just below the bit that props up the ATF dipstick.

Thanks all - non-starter now = starter

[Bob]

Well done.