As i hv become a gauge watcher.  I thoight i would hok up a tachomeyer and the little lights on the three gauge unit so i can see at night.

So, i put the green wire to the neg, red to power source, and blck ground.  It worked, so nxt went to those tiny gauge lights,  i put a alligater clip on the instrument fuse for temp test, and grounded, didnt work. So i turned on the car, and the gen light came on and stayed on.  Wtf!    So i unhooked everything i had fooled with.   Started, same result. Gen light on.

Got meter, tested w car on,  14.24 to 14.4 on meter. 

12.7 to 12.8. car off, 12.6 to 12 8 w car on w brights on.

So i cked VR ground, it was tight.  [Its only about year or so old]  I cked alt,  oddly enough, the ground wire wasnot attached, i guess the nut vibrated off because i hvnt touched it since rebuild.  So i reattched, statrred car. Same result, gen light on. 

I then realized that when i turn the key, before ignition, the gen light usually comes on but now, it doesnt until it starts, almost in reverse of usual operation.

Any idea what i hv done to cause this and how to ck and rectify?

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step 1.
replace the instrument fuse you just blew

Hmmm,   glad to know there are those who understand power.   Thanks Mark.

Continuiing this a little,  where should i hook the power wire to the little gauge bulbs?  

i don't like adding wires into the fuse box to power accessories.  
What i would do would be to run a wire from the start with a fuse link at the starter end to feed a relay, so that there would be minimal pull off the existing circuitry and to prevent a burned fuse box. 

Ok,  well, i had to google what a fusible link was, so its basically a lower resistance wire you attach inbetween the fuse box and the accessory you arecadding, so that if it overheats the wire. The link will burn before the overheating of the wire gets to the fuse box, is that correct?

Because its a nighttime option, would i be lookkngbfor dash lights or headlight wires to attach to.  

Correct —to be protecting the fuse box from overheating as Mark indicated 

you should connect to a wire that works when the instrument lights go on at night to light your additional gauge at night 


Splice into one of the dash lights wiring under the dash that goes on at night when you turn on the headlights 

Pull the negative terminal off the battery to do the wiring connections once you  establish the dash light power wire you will be using. not to case an electrical flash as you did before 

A 12 v wire tester will have a sharp point on it to stick into the  a wires coating to find a hot wire  to be testing when the  headlights go on and off  to be sure you have the correct source

The pig tail wire on the tester goes to ground 


Thanks Tony.  Im try8ng to find the wires now.   

if you want them to dim with the dash lights, then you would tap into the dash lights, and you wouldn't be able to do that with a relay without some extra complications, so you'd have to risk overloading the dimming resistor and connections at the h/l switch.  
If your gauges are non dimmable led or if you don't care about dimming them, you can use the parking light wire to close the relay.  If the gauges are led, you must'nt use the dash wire.

They look like regular bulbs.  I dnt care about dimming. Just want them on for night driving.

I did change fuse and all is bk to normal.  Gen turns on when key is switched over, then fades out when engine starts.  Glad it was only a fuse

Any time you cause an electrical flash in the cars electrical system (  a spark of any kind ) there is a   Very good chance  you damaged the electrical systems —Regulator  internally —located on the passenger side on the fire wall in front of the alternator 

Replacing the regulator will correct the Gen Light from being on —after the engine is running 

Very sure that is your problem here 




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