GT6 Mk.3 Ballast resistor/ wire?

[markcro]

Can anyone tell me where the ballast resistor (says "wire" in the manual) is on a late Mk.3 GT6? And what does it look like.

The manual says that my GT6 should have a ballast wire and should use a 6v coil. I've had my GT6 about 8 years now and when I first bought her I measured a constant 12v (13.8v)to the coil so I assumed that someone must have removed the ballast at some point. And so I replaced the coil for a 12v one. She has ran lovely ever since.
But since last year I have been chasing an intermittant fault which causes her to run like a bag of bolts from time to time. When she comes up to temp and is ran for some time I can measure the voltage to the coil dropping from 13.8 v down to 10.5 and below. Once the voltage drops to 10.5 the engine struggles. And will not restart when hot.
I have replaced the ignition switch which has fixed the hot start issue but not the main cause. Looking at the electrical schematics I see that the only thing left is the ballast wire (if still in place) or maybe bad connection if it was once removed.

Alternatively I am now just temped to run a new switched live feed to the coil and be done with it once and for all.....

Or is there any way that the alternator could be an issue? Although it gives a full 13.8v to the battery.

[Velocita Rosso]

Quoted from markcro

Or is there any way that the alternator could be an issue? Although it gives a full 13.8v to the battery.

Should be 14.45v or there abouts....any less and there is a problem

[markcro]

Hmmm, so maybe the alternator then? I would say that it is original and untouched from new, so may be getting tired.....

But the thing is that when I measure the voltage to the coil dropping down to 10.5, the voltage to the battery remains as 13.8v....
And the voltage drop to the coil is a slow drop down: 13.45v....13.3...13.2....etc. I can see it slowly drop all the way down. Switching on electrical items makes it worse but yet the voltage to the battery remains at 13.8v.

[piman]

Hello Marcro,

are you measuring the coil voltage with the car running or just with the ignition on? Unless the circuit is under load you will not get an accurate voltage reading. Assuming the former, it's strange for the voltage to slowly sag? If your car should have a ballast resistor wire (white/pink from memory?) and to run a 12 volt coil then it must have been by passed so that is the first check. What colour is the wire at the distributor +ve and can you trace it back to it's feed and so check the termination?
Te other thing that occurred is that the coil is slowly breaking down and that's what dragging the voltage down, but it would then be very hot and also I wouldn't expect it to last very long. I.E. it would not recover once switched off.

Alec

[drofgum]

Markcro,
The progressive decrease in voltage looks like a bad connection getting progressively hotter and worse. Since the battery charge voltage stays steady the problem seems to be somewhere other than the alternator circuit.  As a guess a bad splice where the ballast wire has been bypassed could be the cause.
                                                                                              Best of luck,
                                                                                              Paul

[Nick Jones]

Quoted from drofgum

Markcro,
The progressive decrease in voltage looks like a bad connection getting progressively hotter and worse. Since the battery charge voltage stays steady the problem seems to be somewhere other than the alternator circuit.  As a guess a bad splice where the ballast wire has been bypassed could be the cause.
                                                                                              Best of luck,
                                                                                              Paul

^^^^^ I agree with Paul

Nick

[markcro]

Thanks guys for your replies. I will answer your questions all in this one reply.

- Yes I was measuring the coil voltage with the engine running.
- The +ve to the coil is a single white/yellow wire. I note that the loom under the coil has a join sticking out which is shrink wrapped. The join is two white/yellow wires joining to a white/pink wire. Also I see a similar shrink wrapped join near the fuse box- a white/pink wire joining to a white wire. To chase these back to their feed I presume there is no easy way but to cut open the loom and follow the wire back that way?
- Can you measure the voltage at the alternator while the engine is running?  :Where do I take the measurement on the alternator from? Is this not the same as from the battery +ve terminal?
- Can you measure the voltage between the coil + terminal and the battery +ve terminal with the engine running? Should be sub 1 volt ish.  : I'm off to Barcelona in the morning so won't be back to take measurements until next weekend... but also

Just one other thing to add; the last time when I was taking measurements and I had a full electrical load on the engine (main beams, fans etc. on), the coil voltage dropped to 10.4 v (battery +ve voltage was 13.5v) and the engine was really struggling to idle and not cut out. So as a test I connected a cable directly from the battery +ve to the coil +ve and she instantly ran sweet.........

Cheers all, I appreciate the input.

[Velocita Rosso]

Quoted from markcro

Thanks guys for your replies. I will answer your questions all in this one reply.

- Yes I was measuring the coil voltage with the engine running.
- The +ve to the coil is a single white/yellow wire. I note that the loom under the coil has a join sticking out which is shrink wrapped. The join is two white/yellow wires joining to a white/pink wire. Also I see a similar shrink wrapped join near the fuse box- a white/pink wire joining to a white wire. To chase these back to their feed I presume there is no easy way but to cut open the loom and follow the wire back that way?
- Can you measure the voltage at the alternator while the engine is running?  :Where do I take the measurement on the alternator from? Is this not the same as from the battery +ve terminal?
- Can you measure the voltage between the coil + terminal and the battery +ve terminal with the engine running? Should be sub 1 volt ish.  : I'm off to Barcelona in the morning so won't be back to take measurements until next weekend... but also

Just one other thing to add; the last time when I was taking measurements and I had a full electrical load on the engine (main beams, fans etc. on), the coil voltage dropped to 10.4 v (battery +ve voltage was 13.5v) and the engine was really struggling to idle and not cut out. So as a test I connected a cable directly from the battery +ve to the coil +ve and she instantly ran sweet.........

Cheers all, I appreciate the input.

The alternator output is checked by putting meter lead on large spade of alternator and earth...should be just over 14v. This large spade wire goes to the starter solenoid and in turn back into battery
In theory putting the meter lead onto solenoid or  + battery post then they should be the same
You can get `green` on the alternator/solenoid terminals if the terminals are over heating
This in turn allows less charge to flow.....
.....ask me how I know

[drofgum]

Markcro,
The connections you describe for the coil +ve are correct for a ballast wire to supply a 6V coil. The pink with white wire is the ballast wire. A 12V coil will produce weak spark when installed on that circuit. At higher revs misfires can be expected.
                                                                                          Cheers,
                                                                                          Paul

[Pete Lewis]

and the white yellow is the feed from the starter solenoid so you give the 6v coils a 12v boost when cranking   and must be on the starter  feed side terminal of the solenoid

if the ignition feed is still on the white /pink then its def ballasted and you must run a 1.5ohm primery coil.  

if you bypass the lot then you need a 3 ohm coil  

mix and match problems
some ballasted  6v coils are marked as 12v just to make  more  confusion

but a ballasted  system running a 12v coil  @3 ohm will give you nearly half the HT you need and misfires


a 6v 1.5 ohm coil on 12volts will nearly double the HT blow rotors and burn points as the current is now doubled


Pete

[markcro]

Okay after been away for 2 weeks and then other things happening, I just got back to this today. I decided to completely bypass the resistor wire and wired in a new switched 12v wire directly from the battery +ve. I fitted a 3 way small fuse board with switched 12v feed a few months back for an electric fuel pump, so it was quick and easy to run a new feed to the coil.
She then started on the button and purred like a kitten. Now a good drive will be the real test but when up to temp now I am reading a full 14.6v to the coil, rather than the previous 10.5v and dropping. So hopefully this is the end of this problem that I have been chasing on and off for the past 3 years!
Oh and the coil is definitely a 12v and has a healthy 3 Ohms.

I did notice that with full electrical load on the voltage dropped to around 12.4v. 2.2v drop. Does that mean that the alternator is getting tired or is that normal? (Original alternator at tick over).

[GT6 M]

Ballast ona GT3 should be next to coil ont block.
see pics,its an oblong thingy wid 2 connectors,and wite looking

https://www.google.co.uk/searc.....;biw=984&bih=595

M

[system6]

Hi....(sorry to ask a question on Markcro's thread)....
     I've fitted a ballast resistor (gt6 mk3)...one wire to the coil and another to the ignition switch....car runs great!!...the only problem i have is the spark plugs are getting very hot and the core is very white indicating over-heating... could this be caused by the ballast resistor  in-correctly wired ?.. , also...  i'm not sure what voltage the coil is on the car 6 volt or 12 volt , ...any advice geatly appreciated...but please keep it simple as i'm not to good with electrics....

                                                                                     Thanks

[markcro]

Quoted from GT6 M

Ballast ona GT3 should be next to coil ont block.
see pics,its an oblong thingy wid 2 connectors,and wite looking

https://www.google.co.uk/searc.....;biw=984&bih=595

M

Thanks for that! That is the first time I got a clear indication of where to look and what one actually looks like. My car is a late Mk.3 which from the above were fitted with a ballast wire rather than a resistor. And this was the start of my problems as when I bought the car I couldn't find the ballast resistor so assumed it had none. I didn't know about a ballast wire. Anyway the whole lot is bypassed now so I'll see how she runs now.

- System6, I can't answer the heating question, but the best way to find out what coil that you have fitted is to disconnect the connections and measure it's resistance with an Ohm meter. Roughly 3 Ohms is a 12v coil. And roughly 1.5 Ohms is a 6v coil.

Then with the car running measure the voltage to the coil. I'm seeing the full 14.6v (coil terminal to battery -ve) and so I need to use at 12v coil. With the ballast wire in place I was seeing 10.4v but I am not sure if that is normal, but a 6v coil should have been used.

[GT6 M]

Im fairly sure, that even late GTs had it next to coil ont block.
if it did,nt, then some bod,e  es been modding

M

[nang]

On the bottom of a Lucas coil will be a number, ending with either 6 or 12. This will determine which you have.
Tony.

[markcro]

Quoted from GT6 M

Im fairly sure, that even late GTs had it next to coil ont block.
if it did,nt, then some bod,e  es been modding

M

I am not sure to be honest, I'm just going with the advise of drofgum above after I described the shrink wrapped wires near the coil. But then again if someone removed the ballast resistor they may have just shrink wrapped the two wires together. But something in that circuit is dropping the voltage. But doesn't matter now as I've ran a new direct cable for full voltage.

[RobPearce]

Quoted from GT6 M

Im fairly sure, that even late GTs had it next to coil ont block.
if it did,nt, then some bod,e  es been modding

I was under the impression that they did change to a wire in the harness, but it was very late - certainly after the change to swing-spring.