Dash light, brake light issues

[CarpBlazer]

Hi All. Newbie here, just purchased a slightly(very) neglected 1971 K5 and am currently trying to get it back to acceptable working order, as in, drive-able with no cops pulling me over..

Having some issues with:

1) No rear passenger brake light (tail lights work, back up light works, left brake works, new bulb, cleaned connections, new turn signal switch)

2) When ignition is in 'on' position (or when truck is driving) turn signal indicators in dash stay lit solid, dash lights stay on and high beam-blue light is lit. When ignition is turned to ACC all is normal and turn signals light up only when they are engaged, no dash lights unless headlights are turned on, etc.

Could the ignition switch be bad? (just replaced it, but this seems odd as it's sending power to lights in dash cluster that shouldn't be lit and only when in 'on' position)

Will indicator lights in dash stay solid if there's a bad ground in rear brake light?
Thinking also that dash lights staying on and blue hi-beam indicator lit while in 'on' position could be bad light switch?? (have just replaced dimmer switch)

Next step is to get voltmeter and check volts at brake light. I'll update post to what I've found.

Thanks for any insight.