| Author | Message | ||||
     David Geach New User Username: davidgee Post Number: 3 Registered: 02-2022 |
Hi All, I am reinstalling the magneto on my 20/25 GGA60. It was not working when I purchased the car, so it appears to be missing a lead from the Switch Box. The lead is shown as Black on the Electric Wiring Diagram. The lead from the magneto to the HT Distributor is installed. I have refurbished and rewired the switch box, and I don't remember the black wire being there. What does the black wire connect to inside the switch box, is it 12V or earth. Also is it permanently connected to either of these or is connected/disconnected when the ignition switch is turned on. David
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| Jim Walters Frequent User Username: jim_walters Post Number: 373 Registered: 01-2014 |
The black wire from the mag goes to ground when the switchbox is turned off or to battery. The points in the mag are grounded when the switchbox is in those positions which prevents mag operation. When the switchbox is turned to mag, the circuit is open which allows the points to function allowing the mag to fire. So whichever terminal on the switchbox corresponds to those parameters is where that wire connects to. SRH8505 SRC18015 SRE22493 NAC-05370 www.bristolmotors.com | ||||
| David Geach New User Username: davidgee Post Number: 4 Registered: 02-2022 |
Hi Jim, Many thanks for your kind response. So by my reading of your email, by earthing the black wire stops the magneto from providing a spark to the distributor and thus stopping the engine. I also read by Earthing the black wire I assume this does not cause any damage to the magneto. I just did not want to damage the magneto, especially as I've paid alot of money to have it checked over. Unfortunately I have just rewired the switch and fuse boxes, but I missed off this lead, as it was not there when I started the job. Removing the switch box is a fiddly job due to lack of room. But at least I now know what to do. Many thanks again. | ||||
| Jim Walters Frequent User Username: jim_walters Post Number: 374 Registered: 01-2014 |
You are correct, earthing this wire stops the magneto from working. It is designed to work this way and will not damage the mag. SRH8505 SRC18015 SRE22493 NAC-05370 www.bristolmotors.com | ||||
| David Geach New User Username: davidgee Post Number: 5 Registered: 02-2022 |
Hi Jim. Many thanks for your help, it is appreciated. I will now have a go at installing the mag. Great website/forum. David | ||||
| David Geach New User Username: davidgee Post Number: 6 Registered: 02-2022 |
Hi Jim, I have now reinstalled the magneto, and set up the timing as best I can. Unfortunately I'm not getting a spark at the spark plugs. The timing may be out, but I don't think this is the cause of the problem. I get a spark at the spark plug when it is connected directed to the high voltage lead from the magneto, ie., without the distributor in the circuit. However, I'm not getting a spark from the spark plugs when I connect the magneto high voltage lead to the distributor. Connecting a spark plug tester, of the type where you can alter the spark gap, I notice the spark strength is considerably less from the magneto than that compared to the spark via the coil. I suspect the magneto voltage is just strong enough to jump the spark plug gap, but not across both the distributor arm gap and the spark plug gap. Why is the magneto voltage so low? The magneto has been overhauled by a specialist (unfortunately he has now retired), so I am not sure what I doing wrong. Any help will be appreciated. David |
Wiring Diagram