hey guys i am in need of some advise on a problem i have been having... here is some background info

1986 toyota extended cab sr5 w/bobbed bed
reverse lights haven't worked since i got the truck ( not the problem i am addressing, but figured you should know)
the truck came with a trailer harness installed

i replaced the master cylinder a few weeks ago, and noticed that the dash lights/ tail lights stopped working, and now when i turn too many electronic things on(heater, wipers, stereo, headlights, blinker) my car will start to missfire. every time i turn something on i can watch the little voltage meter in my dash go down... so i figured i must have bumped a wire loose when i was under there connecting the master cylinder to the clutch pedal... i have looked multiple times, and cant find anything that looks like it is disconnected...

also i was messing with my stereo around the same time( swapped head units), but I'm pretty sure its from when i did the master cylinder ( could be wrong though )

i have checked/swapped the "tail" fuse, and it doesn't appear to be blown... i also tried jumping the tail light relay, and it just got really hot, so i quickly pulled the jumper wire out of the terminals...

i am running out of things to look for, i was reading that there is an orange illumination wire for the radio that can kill your dash lights if you hook it up wrong to the back of the headunit... but i couldn't find that wire when i installed my deck..

if there are parts that are hard to understand let me know and i will try to figure out a better way to explain what is happening

 

also forgot to say that the battery and alternator both tested good

 

fixed the dash/ tail light problem (dimmer switch pigtail wasn't clicked in all the way)

... but i am still getting voltage drop everytime i turn on my accessories.

 

thinking i might try doing the big 3 grounding mod this weekend, and see if it helps at all

 

I know you listed several accessories, but are there any that you turn on and don't notice the problem? If it happens no mater what you turn on I would look for a more 'centrally located' item thats causing the problem. It is possible for your alternator to be weakening and not be able to keep up with powering everything you want on at the same time but still test good.

 

Did you ever figure out what was causing the problem with the electrical system? I have almost the same issue with my 86 4 runner.Turn on any thing and the engine will start to stall and back fire.
Thanks