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MG MGB Technical - Timing Light connection, MGB.

So my dear wife bought me a snazzy timing light for Christmas. After 40 years, she seems to just know.
For the power supply to the light, the instructions include "Connect red clip to battery positive terminal; connect black clip to battery negative terminal or chassis ground". In the case of the BGT (1973), I'm thinking to avoid stringing cables to the battery it will be logical to attach the positive alligator clip to a brown wire feed: examples include starter motor at the solenoid, or fusebox at # 7 or 8. The grounding will be to chassis. Anyone any thoughts on the positive feed?
Thanks all, and very best wishes to all on this BBS for the New Year.
John.



J P Hall

I always do it to the fusebox, white connection i.e. second one up front, and somewhere on the alternator.
paulh4

Thanks Paul - is "somewhere on the alternator" your grounding wire? I originally thought I should use an "always live" source, but I can see it doesn't matter if it's ignition fed.
Also, since I have Lumenition electronic ignition, not the moving points, is there any point (sorry) in looking for dwell angle?
John.
J P Hall

I normally connect to the solenoid, but I have the separate solenoid for an inertia starter.

In the absence of that, I would opt for the fusebox.
Dave O'Neill 2

We use a spare battery to make life easier. Lots of folk have a jump pack they could use too.
Peter Burgess Tuning

Ah - so Peter you've soothed another uncertainty I had - whether once the motor was running, the car's battery had any relevance at all in the timing exercise, or whether an outside power source could feed the timing light. Excellent. Dwell angle relevant when there are no points?
John.
J P Hall

JP - yes for the earth/ground connection.

Years ago I found using the inductive pickup type for diagnosis on a non-runner it didn't flash and thought it would need an external battery, but that may have been down to the battery on the car at the time as it was flashing OK just now.

I also wondered if one would need to link the car and external battery earths to 'complete a circuit', but again just now using my lithium pack it flashed without.

Dwell angle should give a reading with electronic ignition, but will vary greatly depending on whether it is fixed dwell like points or variable dwell which will give a much lower reading at low revs, increasing as the revs rise.
paulh4

I use the bottom connection on the fuse box and a cylinder head nut for earth.
Paul Hollingworth

If you have a volt function on the timing light then using an external power source reads the power source not the car.
We also use our external power pack/battery to power up the coil if we are trouble tracing. We also have a spare points distributor we can easily fit and power up independently of the car wiring so we can test for wiring/ignition problems. Same as having spare fuel pump pulling fuel from a petrol can if needed.
Peter Burgess Tuning

Great information from guys with way more experience than me - thank you gentlemen. I look forward to having a play. Incidentally Paul 1, I benefited hugely from your photos of choke linkage/lever settings in Hammer & Spanner, correcting everything with good results. Just waiting for new floats to better adjust my fuel levels (recent discussion), and it'll be "job done".
Hope this is of interest to others. John.
J P Hall

I've been carrying a spare distributor and fuel pump on long trips for more than 30 years and 160k, used the pump once so far when rapping didn't work.

JP: Thanks for the kind words, glad to be of help.
paulh4

This thread was discussed between 01/01/2024 and 02/01/2024

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