2 tach questions

OonDeanisS · Mar 30, 2005

sorry the first is long, but i didnt want to leave anything out. thanks

1. My tach used to work before i took off the dash and now only the light comes on, no RPM. Its autometer. I know the black should be going to ground, but instead it was linked to a blue wire that is now not attached to anything, but i think it was going to the ignition switch, which i do not know where that is... The red wire that SHOULD be going to the ignition switch is linked to a black wire going to the battery ground. I know it worked before, so maybe i just need to find the ignition switch and link the blue(black) wire to it.... or should i link the original black to the ground and get the red wire to the ignition switch?

2. the tach backlight now only goes on with the headlights and stays off with the parking lights... where should i link the wire to fix this?

HISSIN50 · Mar 30, 2005

brown wire under the dash is the parking light wire. im not sure of the color of that wire on the back of the headlight switch. i might tap into the dimmer circuit (if you are sure the wiring is sound). you can do this at fuse 13, the back of the headlight switch, etc. if using the switch, put a test light on the parking-light hot wires. one will dim (the test light) with the rotation of the dimmer switch. that is the right wire, if you want to have the backlight dim.

i would hook the tach up the way it is supposed to be hooked up, myself. i did not know the air core components could take absolute values/ reverse the signal.
good luck.

OonDeanisS · Mar 30, 2005

not sure what you mean but thanks

HISSIN50 · Mar 30, 2005

OonDeanisS said:
not sure what you mean but thanks

That's ok, I did not understand why things were wired up backwards on your car.

What don't you understand in my post? I would hook the tach up properly and use the dimmer circuit for the lighting. I posted different ways to do things since you did not provide information on where you tapped power for the lighting.

good luck.

OonDeanisS · Mar 31, 2005

i didnt understand why the previous owner would do that either... but it worked.

After reading your post again i get what you're saying... I wish i had a test light lol

HISSIN50 · Apr 1, 2005

OonDeanisS said:
i didnt understand why the previous owner would do that either... but it worked.

After reading your post again i get what you're saying... I wish i had a test light lol

cool - I just re-read my previous post; I think it came off as rude. my apologies (I do like for people to post when they dont understand my ramblings, but I need to know which part was not understood. I am posting to try and help and if my post was not clear, it helps to know what was not understood so i can be [ or try to be] more articulate).

it sounds like someone wired the gauge up just wrong or they wired it as if they had a reverse ground system (a la some old Brit cars).

so simply said, i would start over: grab key-on 12 volts somewhere that is close to your gauge. one can use a key-on hot fuse in the fusebox if one does not want to tap into another circuit.

for lighting, i would just grab power from fuse 13. there are dirty ways to tap power from a fuse, but parts stores sell fuse taps, which are a plug-and-play means to add a circuit to a fuse. you could use one for the lighting and for the 12 volt feed for the gauge.

a test light is a MUST HAVE for any one who is hands on. Harbor Freight puts them on sale for 99 cents a piece. i keep 5-10 on hand (i keep one in every car's trunk for roadside diagnostics). you can also get a 4 dollar DMM on sale there - another must have. i keep several of those around for when i break one. so for 5 bucks, you can have one of each and be ready to go!

good luck with it.

OonDeanisS · Apr 1, 2005

how do i know which wires are 12 volts Key on?

HISSIN50 · Apr 1, 2005

OonDeanisS said:
how do i know which wires are 12 volts Key on?

with a test light: connect one side of the test light to ground and the other to various power sources. some sources will not illuminate the test light until the key is turned on (e.g. fuse 9). here is a list (note that Tom's schematic is based on an 88 so your model *might* be different. just check real quick to make sure). here is a run down on fuses:

http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

good luck.

OonDeanisS · Apr 5, 2005

ok i connected the black wire to the ground, and i tried the red wire with every single fuse and even the lighting wires and no RPM signal still... i dont understand whats going on (or what isnt)

HISSIN50 · Apr 6, 2005

OonDeanisS said:
ok i connected the black wire to the ground, and i tried the red wire with every single fuse and even the lighting wires and no RPM signal still... i dont understand whats going on (or what isnt)

is the neg (often green) wire connected to the negative side of the coil?

OonDeanisS · Apr 6, 2005

no i have an MSD and the green wire goes to the side of the box... should i try putting it to the neg of the coil?

HISSIN50 · Apr 6, 2005

OonDeanisS said:
no i have an MSD and the green wire goes to the side of the box... should i try putting it to the neg of the coil?

oops, my bad. I missed the box. i would not try wiring the tach off the coil - one is not supposed to, as i recall.
i do know of one guy who does that, but just because he pulled it off does not mean that i would try it, nor would i suggest others trying it.

good luck.

OonDeanisS · Apr 6, 2005

thanks hissin for all your help... but i still cant figure this one out. I wish you werent the only one who would give my post the time of day, but i guess it is kind of a stumper.

HISSIN50 · Apr 7, 2005

OonDeanisS said:
thanks hissin for all your help... but i still cant figure this one out. I wish you werent the only one who would give my post the time of day, but i guess it is kind of a stumper.

yeah, i know how you feel. i have had some threads not get much help, so when i see one not doing too hot, i will post on it even though i have no great ideas (just so you dont know it was not ignored and to bump the original poster).

but this sounds like one of those things where if I or any of the number of knowledgable stangers was there in person, we could make something happen. when stuff is done strangely, it can be hard to sort out from a keyboard.

so if the gauge is dead, how was the wire that goes from the tach to the coil looking? check the connection of it at the coil. i know with mine, i did not want to booger up the wires, so i was creative with inserting a wireless terminal connector which could come loose at some point. if you test the tach signal wire at the coil itself and then again at the end of the wire (near the gauge), it should be lookin the same. if not, you have found a bad wire or connection. now i dont know if this is even the issue, but am just posting what i would do with the info given.

the good thing is that the wiring is so simply on a tach, it should not be too hard to figure out. good luck bud.

OonDeanisS · Jun 21, 2005

The wire looks fine, but it goes to the MSD box and not the coil.

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