I have tried splicing from the fuse box using a fuse tapper on the engine fuse but they aren't getting enough power.

 

You should be using the fuse box signal as trigger only, the power for the gauges should be coming from the battery via a relay trigger by a switched 12V.

 

I don't know much about relays and things, is there a guide or another thread that explains what I need and how to wire it?

 

I suggest Google some simple relay diagram, they are pretty simple device, but you should have full understanding on how it works before trying to wire one up.

 

something along these lines then? I have basic understanding of wiring so I can manage this.

 

Yup, 86 85 pair is the trigger, while 30 87 is the load.

 

Is that why my volt meter bounces to the radio and turn signals?

 

awesome thanks, also though, if I got a 5 prong relay with an 87 and 87a can I run 2 gauges off of it?

 

might be, the reason I started this thread is because my gauges were reading lower than usual when ever I put on the brakes or headlights. They werent getting enough power from the fuse box.

 

Hard to tell unless I know how everything is wired in your car.

They are opposite, 87 is normally open (on when 12V trigger is active) and 87a is normally closed (on when 12V trigger is NOT active).

 

Ok I see. Well then can I run both gauges from the one wire out of the relay or could I get a different kind of relay with 2 outputs?

 

Most of these automotive relay are rated at 20-40A, so that output is more than enough to feed all your gauges, just run them all in parallel. I run a Painless wiring fuse block that has a 20A relay, and that feed all the add-on electronic like gauges, EBC, WI and WB controller.

 

I have everything set up and I tested all the wiring and at the end of the wire coming from the relay (87) to the gauge it gets ~12.3v, and turning on the headlights drops that to ~12.1v and the brake lights on top of that drop it to ~12v. The problem is that my glowshift oil pressure gauge is showing a drop in oil pressure when ever either head or brake lights (or both) are on. I may not know much about electrical stuff but a .3v drop shouldn't take make the gauge go from reading 20psi down to 0psi at idle or from 60psi to 56psi at high rpm, yet it does. I also have a glowshift water temp gauge which ran from the same power source and doesn't have that problem, or atleast it is so minor that I can't see the difference so I am just hoping its the oil gauge that is faulty, because I don't know what to do to fix the issue if it isn't...

 

That’s with the car on? Your battery source should be between 13.5V-14.4V when the car is running.

 

that is what it reads with just the ignition on. with the car on and running it puts ~14.1v to that wire and with both the head and brake lights on it still drops by about .2v. But again, I may be wrong but I don't think that should cause any difference on the gauge...

 

Yeah voltage drop is normal with load, but as long as your voltage is above 12V there shouldn’t be any difference in your gauge read out. Even if you drop below 12V, a well designed gauge will still read the same as the regulator that drive the reference voltage should accept 9-15V.

 

Im getting a replacement tomorrow and see if thats the case. I hope so because if its not that then it might be the battery but that would be really annoying (I replaced it the same day I started having problems).

 

~14V is fine, I don’t think it’s your battery/alternator. Where are the gauges ground to?

 

On a screw that holds a metal line or something onto the drivers side firewall. They are both ground through that wire but like I said before the temp gauge seems to work just fine off that ground.

 

Seems like a gauge issue to me, you can measure the input voltage at the pressure transducer to see if it changes as your 12V source to the gauge drop. It should remain at 5V, but if it changes then your gauge is sensitive to voltage fluctuation.

 

A replacement gauge is arriving today so I will find out then. I really hope it is because this has been bugging the crap out of me all week.

 

Well, now I have news. The new gauge did not fix the issue and unless I just happened to get a buggered one straight out the box, that is not the problem. It also isnt the supplied cable as I replaced that with the new one and it did nothing.

The big thing though: I also noticed that when ever I turn or the headlights or press the brakes, my rpm goes down and all the other original gauges drop a little. It seems like something is sucking the power. I also tried a different battery and it didn't change anything. I'm going to try replacing all the fuses since they all look old and that's the easiest next fix. Otherwise I have no clue what the problem is.

 

If everything drop together then you are chasing a bigger problem, first check your alternator, make sure it is pumping out enough juice to handle everything.

 

It is, sadly... lol. I am starting to think my main battery ground or some other grounds are losing connection. I noticed a few weeks ago while driving that all my gauges were reading lower than usual especially whenever the headlights were on. Like my voltage was lower with headlights on (dropped from 14 down to under 12 volts) and my oil pressure gauge would consistently read lower at idle, when usually it always read 30. So that got me into a rabbit hole about gauges and their accuracy which lead me to getting the aftermarket gauges so I could atleast be certain of how my car was doing. Initially I had been told it could be a grounding issue but then decided to go with the inaccurate gauges idea because that seemed easier and (at the time) more likely. But now with these problems after getting a new battery, checking with a different more powerful battery, and rewiring almost my entire circuit, I can't think of anything else. Also, I am 95% sure it is the stock wiring harness, even though the engine was replaced with a crate 13b. It has all the corrosion and dirt and brittleness of 34 year old wire, plus on the receipt for the installation, it said nothing about the installation or purchase of a new wiring harness. So I am going to try cleaning the shock tower ground and possibly the starter ground tomorrow, and if all else fails I will remove everything I did and take it to a trustworthy shop I know of nearby that should be able to find and fix the problem for me. I really hate not fixing and working on the car myself but I have to admit defeat sometimes...

 

I'm afraid you have to chase down the main issue first, start with the alternator.