No power at coil

[vetanari]

Hi,
I've hit yet another electrical problem on my 1968 P5b. Tjere is no voltage at the coil. I do get a voltage at the fuse box

I'm tempted to run a new cable to the coil from the fuse box  but I'm worried that I might be bypassing something vital!  I tried it as a temporary fix and the car starts but I don't want mess things up any more than they are already!

There is definitely a connection somewhere in there (different cable arriving at coil than the one leaving the fuse box )

Cheers

V

PS There are 2 cables leaving the ignition circuit One to the coil. Has anyone any idea where the other one goes? 

[markymark]

Hi,
From memory, there is a +ve feed that comes from the tachometer to the ballast resistor and then to the coil. I had an issue a few years ago that was fixed by me running a new cable from the tacho.
If you run a cable from the fuse box, the engine will run (tacho not working) but be careful of bypassing the ballast resistor as voltage will now be too high. This is assuming you haven’t got electronic ignition fitted which may not need the ballast resistor.
Hope this helps..
Mark

[Phil Nottingham]

You need to consult the wiring diagram!

The coil feed must never be taken from the fused side of the fuse box ignition supply only the WHITE cable


Furthermore as a 1968 car it should have a ballasted coil and the ignition feed must go via the Ballast resistor at the side of the 9v coil and at the other side of the resistor another cable goes to the starter solenoid shunt which is only live at 12v when cranking the engine.

The fault can therefore lie in a number of places but wiring direct to a 9v coil is not a solution unless the coil is swapped to a 12v version as a ballasted coil was found not necessary anyway and was dropped on later cars

[stirlingmg]

Sounds to me like the ballast resistor has failed, I would locate it & check if it has input & output.
If it has the former but not the latter then there lies the fault. Vehicle electrics, particularly on stuff of this era are not complicated. It just needs a methodical, common sense approach

[vetanari]

Thanks for the replies. I've managed to fix the problem (a connector at the ignition switch )
Engine now running
The car is a bit of a frankenstein's monster, I'm afraid. It's a saloon but has the tachometer and I'm pretty sure the gearbox is from a later model. but I'll get there in the end

Thanks again

V

[Phil Nottingham]

Pleased it has sorted and you have updated your query for the benefit of other owners to learn from.

All the success with your efforts in the future and I ma sure you can sort it!