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Home > Help Needed / General Tech Chat > Ignition Relay

Turbocod

8 Posts
Member #: 11807
Junior Member

Hi, just fired up my project for the first time, supercharged 998.
Running megajolt and edis system, so did a test by cranking it over with no fuse in the megajolt so it fires in limp mode with edis, fired up pretty much straight away, hooray!
Have used a relay to provide power to the coil pack, edis and megajolt via another fusebox, relay is engaged from the white wire (main ignition) from the ignition switch.
When I turned the key off, the ignition warning lamp glowed, and the engine kept running. Had to pull relay to kill it. When relay is reinserted it doesn't engage again until the ignition is switched back on.
So, is it feedback voltage from the charge light keeping the relay engaged and so keep running (until fuel in carb is gone)?
Has anyone else had a problem like this, and would direct feed instead of relay prevent it?
Thanks in advance


Rod S

User Avatar

5849 Posts
Member #: 2024
Formally Retired

Rural Suffolk

Without seeing your modified wiring in diagram form, I can't be 100% certain but it is very likely to be a backfeed through the charging light circuit especially if the relay you have used has a nice high operating coil resistance (ie, if it only takes a few milli-amps to hold it latched).

It was a very common issue on certain MGB, Triumphs etc around the era of early Lucas electrics and alternators and especially when accessories were added that used relays.

The "standard" fix is to put a diode (something like a 1N4001) in series in that wire to the bulb so it can only be forward fed through the bulb to energise the alternator field and not let anything backfeed.

Schrödinger's cat - so which one am I ???


Turbocod

8 Posts
Member #: 11807
Junior Member

Thanks, pretty sure its feeding back and energised still, will try direct off switch, and if still does it, I'll take dash out and remove bulb which should break circuit and see if problem and if so rectify with a diode.


Turbocod

8 Posts
Member #: 11807
Junior Member

Relay linked out and still runs on, but if alternator unplugged it cuts with key immediately, so ordered up some diodes and will fit along with wiring the rev counter. Cheers

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