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MG MGB Technical - Front and rear sidelights always on

Hi
Can you assist on this please?

Since fitting an Accuspark ignition system to my 77 mgb roadster the front and rear sidelights are on all.

The lights will not turn off.

The other thing is if you actually put the light switch to use the headlights the car cuts out !!

Any ideas?

Thanks so much
Steve
Steve Mitchell

It sounds very much like the accuspark earth lead has been connected to the sidelight circuit, so it is earthing through the sidelights. When you switch on the lights, you are then getting 12v on both sides of the accuspark, thereby stopping the engine.

You need to revisit the way it has been installed and check where it is earthing.
Dave O'Neill 2

Yep--what Dave said
It's interesting though how it could get like that following the hookup instructions, I'd really like to see a pic of what has been done there.
William Revit

As a 77, it would have ballasted ignition. Generic instructions suggest connecting the electronic trigger to the fuse box for 12v. /if connected to either of the top 2 fuses (or if the fuse box is upside down).....Maybe
Michael Beswick

Maybe the earth lead has been connected to the top two fuses in the fusebox i.e. the parking lights. The 12v lead having been connected to the one below that i.e. ignition.

Normally if the fusebox is reversed you can't switch off and the ignition is on all the time.

Be carful about polarity, the Accuspark may be polarity sensitive.
paulh4


I have a '77 with Accuspark just fitted and the tach is acting strange.

It performs normally up to 3500 rpm then just stays stuck there with no movement until I throttle back down.

Everything else functions normally.

Thanks.

Tommy
TF Springfield

Where does the Accuspark pick it's 12v feed from? If from the coil +ve try connecting it to the front of the 2nd fuse up in the fusebox - white/brown wires. Unless the coil and it's wiring has been changed the voltage on the original ballasted-feed coil +ve is continually switching between 12v and 6v. Doesn't always follow but it could be that.

People often mess up the coil type and wiring when they fit electronic ignition as manufacturer info can be confusing if not incorrect.
paulh4

I do have the blue AccuSpark coil which is fed with the ballast lead.

Sadly, the previous owner had attempted to do some major rewiring and I'm having to trace wires in order to find a 12v direct feed from the ignition switch.

Currently the second fuse up from the bottom is fed from the coil which is of course ballasted.

Thanks for your guidance, I'll persist.
TF Springfield

It's the other way round.

The white/brown comes off the ignition relay and feeds that fuse, other unfused ignition circuits like fuel pump and overdrive, and via that fuse most of the fused ignition circuits as well as the ballast resistance and via that to the coil. Or at least it did originally.




paulh4

Just tried connecting the +AccuSpark lead directly to the battery +, same result.

It's almost like there's a physical stop inside the tach that won't let the pointer move past 3500 rpm. I doesn't jump around or anything, just stays stuck until throttle down.
TF Springfield

Could something jamming the movement, try giving the glass a sharp rap with a knuckle.
paulh4

Any suggestions on timing for a 1977 USA car with cat removed and Accuspark ignition?

I'm trying to finish up previous owner's work!

Many thanks in advance.
TF Springfield

Short of a hammer, knuckles haven't worked so far.
TF Springfield

If it's low compression then probably the book strobe figure of 10 degrees at 1500rpm, vacuum advance disconnected and the source plugged. Cat-less and Accuspark shouldn't make any difference.

If it's high compression then it will depend on the grade of fuel being used, advance just short of pinking at any combination of throttle opening, rpm and load. If you try to do that with low compression you can end up stalling the starter before you get pinking.
paulh4

Thanks for the input, too many conflicting opinions out there.

Worked perfectly, engine purrs now.
TF Springfield

Probably on the wrong thread here but what the heck:

'77 USA spec B, exhaust header is not original (cat deleted), Weber conversion installed, only thing holding exhaust header on is two nuts at either end of header. Big washer that holds intake manifold on does not touch the exhaust header flange. Should I add shims to ensure washer contacts both intake and exhaust flange?

Thanks.
TF Springfield

When manifolds are changed you can end up with a step between the two halves on some bolts, stepped washers are used to equalise https://grassrootsmotorsports.com/forum/grm/need-some-stepped-washers/103145/page1/
paulh4

This thread was discussed between 26/10/2023 and 14/12/2023

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