My guess is that you have a connector or two common to these circuits that is dirty or partially oxidized so that it's not making 100% contact at all times. It is probably on the low-amperage side ahead of the relay box. Trace back from the relays, disassemble the connectors, inspect and clean with silicone spray then reassemble.
Owner of Loud Pedal Performance in Mocksville, NC, specializing in automotive restoration and customization.
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