ultra strange electrical problem

I have a 1992 Pathfinder SE...I have had it since October last year, the issue is that the headlights dont work properly, daylight running lights only and one high beam ( Im in Canada - daylight running lights ). it was worse before I changed the daylight running module..before the headlights would jump from one ability to another or no lights at all. now at least it has stabilized to what I describe above. just two days ago I had an alarm system installed..Immobilizer, sound alarm. I went to disarm the alarm and opened the door and the alarm went off and fiddled with it to get it to stop and reset. but during that process my headlights went to full function status including both highbeams for about an hour, then back to what it was before. my dashboard lights even came on as they did not work before either. the alarm install guy replaced a bad fuse to even get my stereo to work which also did not work...is it just fuses?

so how is the above scenario ( apart from the bad fuse for the stereo )  possible?

everything in my vehicle works but there is something that is preventing what doesnt work to stay that way...like a fade in electrical power...is that possible? what would it be?

my mechanic who is an all round expert said he would install a relay system to bypass whatever was bad in the vehicle ( possibly the module in the steering column that controls the commands to the headlights - apparently an expensive part ) to get juice directly from the battery and have the entire range of functions for my headlights work properly. he wants $300 for time and parts. fair? can I do it myself?

From what google returned, it seems the Pathy doesn't use relay, it's a plain column switch that is often problematic but fixed by cleaning. (No relays? At least they scrapped Datsun's ground switching!) And I found nothing about any module etc that sends commands. I doubt a replacement switch would cost anywhere near $300. If it did, I'd get secondhand. Some suggest fine grit sandpaper or emery for contact cleaning, I presume therefore that the contacts get black and pitted. If they still appeared clean, I'd suggest contact cleaner, else maybe some Coke (A Cola - but wash it off afterwards), or a wipe with an abrasive rag. Maybe steel wool - I often use the remaining (green) strip on a long defunct sponge-type scourer pad. Also check that the contacts make and break properly. But I'd look at fitting relays in any case. I find it hard to believe they aren't fitted as standard - any high-current switch will eventually fail (my 1965 vintage switches only last 30 years), but using relays will extend their life until mechanical (rather than electrical/contact) failure. Plus the improved lighting that results - especially with halogens. And the relays can be an "all-front" job. That involves intercepting the plug behind the headlights and using them to energise the relay/s (86 with GND to 85), and you run a new power wire from the battery with a near-battey fuse to relay pin 30 with 86 to the respective bulb. There may even be kits online for the job. I use self-resetting circuit breakers for my lighting circuits (kinda obvious why isn't it?), but I also separate the hi from low feeds - ie, 2 separately fused/breakered power wires.   (Actually I use one breaker and relay per filament, but I may revert to one for each - 4 or 6 relays is excessive for normal use when 2 or 3 will do.) The DRLs complicate things depending on how they are achieved. If the DRLs are the normal main bulbs/filaments in series, then a different relay arrangement will be required, so check BEFORE fitting relays. But I'll wait for feedback regarding that. BTW - another issue may simply be bad contacts. I suggest rotating all same-sized fuses (though rare with newer "blade" fuses, I have known of some to intermittently go open circuit), and disconnect & reconnect plugs etc. That's usually enough to remake a good contact (which solves the majority of electrical problems), and it moves troublesome fuses to another circuit.