No Power To Coil

[Leeham]

Hi all loooking for some help with our petrol 1989 T25 Hitop 1900cc watercooled camper

Problem is there is no 12v going to the coil. Have been through all the fuses in the glove box and all seem fine so gave the mechanic a call.

Mechanic came round and used 12v from elsewhere in the enigne bay and the van started first time and drove it just round the corner to his garage with no problems.

Possibly related, he also noticed what we think is a temperature sensor which had come loose inside the engine bay near the coil which he said he could see shorting- there is also no power to this as well.

So far the ignition switch has been changed and the fault remains.

Mechanic opened up a junction box on the left hand side in the engine bay and found another relay. Does this has anything to do with power to the coil? I've added a photo of this as we're not sure what it's for.

Our mechanic is very good but he doesn't really do electrical work on vehicles, so before calling an auto electician I thought I'd ask here first in case it's something we may be able to sort out.

Could it be another fuse hidden away somwhere, or does the temperature sensor need replacing first before the van will start without taking power from elsewhere?

Any help on this would be fantastic

Pic2.jpg

[bigherb]

No fuses on the coil circuit.
Do other things work with the ignition such as the dash lights?
The black coil cable goes through a multi-plug connector in the black box check its connection, there is no relay. Then it goes to a multi-plug (plug D) in the rear of the fuse box, not unknown for this connection to melt.

[937carrera]

Wiring diagram first - assuming you have a DG engine

http://syncrosport.com/info/wiring/VW_T ... _SP_DG.pdf

Look at page 3

The feed to terminal 15 on the coil is direct from the fusebox, it is unfused and comes out of connector block D, pin 23.There is a single connector block, T1c, located in the engine compartment plastic junction box

Terminal 15 in the fusebox becomes live from the ignition switch, page 2, black wire goes to terminal block A, pin 8.

Your mechanic should be able to check the circuits out with that knowledge

(looks like Bigherb beat me to it)

[bigherb]

it is unfused and comes out of connector block D, pin 23.

Err, pin 15

[937carrera]

According to the current flow diagram connection D15 is the supply wire to the coil, though D23 is fed by the same internal connection, but the wire isn't connected there. Either should work

[Ciaraneng]

I'm reviving this thread as I have pretty much exactly the same symptoms. I was doing some fault finding on a mis-firing issue and was using the thermoswitch (F35) as a source of voltage for my timing gun. I had 12 V there for a while and then seemed to lose it along with the voltage at terminal 15 on the coil when I accidentally shorted the thermoswitch supply. As bigherb points out, there are no fuses on this circuit so it's strange that I lost voltage. The ignition switch seems to work in that the engine turns over and I have lights etc. Does anyone know the easiest way to locate a fault on the ignition-to-coil circuit? Any thoughts what caused the fault or if shorting the thermoswitch circuit could cause it?

[937carrera]

You'll lose the 12v if you melted the wire or internals on the circuit board.

Time to test for voltage at those terminal connectors, and a continuity test end to end from those terminals. Wiring diagrams from the usual syncrosport website

[Ciaraneng]

Thanks carrera. When you say circuit board are you talking about the board within the TCI control unit (N41)?

Is it best to work back from the coil or forward from the ignition?

[937carrera]

Sorry, loose language, i meant fuse board, where the terminal connections are.

I would start at the terminal connections in the fuse box, and depending on the answer move backwards to the ignition switch, or forward to continuity test

[Ciaraneng]

The challenge is finding pin 15 or 23 amongst this mess

[937carrera]

Ah,

I just checked against your rebuild thread, this is an early DG isn't it, with ceramic rather than blade fuses ??

The instructions above were for the post '87 vans, as it says in the wiring diagram. They have connector blocks rather than spade connections. I can't recall an online source for an early wiring diagram for non US vehicles. Do you have a Haynes ?

[Ciaraneng]

Yes, early DG. And I have the Haynes but it has the same wiring diagram as the one linked to above. I'm wondering now if the early DG had a fuse on that circuit. I'll check my fuses first. Also, there has been significant rewiring done on the van and a fuse may have been added in.

I'm thinking I'll chase the black wire from the ignition back via the fuse box to the engine bay and try to locate the break.

Should be great fun!

[Ciaraneng]

Hi folks. The wiring diagram seems to point to connector T1a and it's marked as "single in connector housing". Is the connector housing the black box in the engine bay? Thx.

[937carrera]

I'm with my Haynes at the moment.

The thicker of the black wires is the one which provides the feed to the coil, and then to the idle valve and thermoswitch.

The connector you are referring to is described as "Single connector, engine compartment junction box" on page 12.17

So, yes

update:

I just noticed that that wiring diagram is for the later fusebox too, so I dug out my Aircooled Haynes. If the early WBX is the same as the Aircooled, then it is an unfused feed from the ignition switch to fuse 12 and straight onto the coil with no connector. The coil does not go through fuse 12, it just picks up the feed from that point. Fuse 12 fees the horn, so you can either put a meter on for 12v on the output side, or simply sound the horn to make sure the connection from the ignition switch to the fusebox is fine

[bigherb]

Hi folks. The wiring diagram seems to point to connector T1a and it's marked as "single in connector housing". Is the connector housing the black box in the engine bay? Thx.

Yes,T1a is a single connector in the black box in the engine bay.