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6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc

405 ignition problem

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Old 08-09-23, 05:12 PM
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Default 405 ignition problem

The ignition switch on my 405 becomes blisteringly hot - anyone else experienced this?
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Old 08-09-23, 08:07 PM
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You'll have to get this sorted. Heat means resistance, so (best case scenario), you've got some loose connections behind the ignition switch.

But get it inspected, diagnosed and sorted as soon as you can. If it gets so hot that wires melt, you could get a potential short circuit that could go right through the wiring loom back to the alternator/generator/battery and cause a fire.

Luckily, you've noticed this and can get it fixed!
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Old 08-09-23, 10:18 PM
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If the wiring diagram is the same as for the aerodynes all the power goes through that switch. If any of the contacts are not tight the switch will get very hot, especially if you are using 65+ watt qi bulbs in the headlights.

Last edited by peterg; 09-09-23 at 06:29 PM.
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Old 09-09-23, 07:50 AM
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Quick responses much appreciated and have confirmed my fears - will get it over to Mark at Coleman Classic Cars on Monday for an inspection
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Old 09-09-23, 02:57 PM
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I had this exact problem on my 401 many years ago. A previous owner had connected so many things off the ignition switch and the switch can’t handle that much current draw. The worst was the electric radiator fan that had been installed. The car would start and run fine. As it got up to temp, the fan would turn on and the ignition would have problems….. the power to the coil was now too low to run well.
I rewired the system, installing relays, and this took the load off the switch itself. Now the switch only sends a signal to a relay to energize the fan and other accessories.
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Old 09-09-23, 04:05 PM
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Thanks - will report back on diagnosis and cure
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