JohnCalvin

Bought a tach from summit and i don't know which side of the coil the green wire goes on... I've done some research and found people saying both negative and positive side.... I have an electric ignition set up, msd 6al, blaster coil 2... etc... so... put it on the negative side or positive side? If i try it on the negative side first and i'm wrong will anything blow up on me?

LCC

Negative side of the coil. All tachs use a pulsed to ground signal.

JohnCalvin

ok thanks... I have it on the negative... and i spliced the 12v wire into what i thought was 12v source under the dash but when i start the car the tach doesn't do a thing.... any advice? Anyone know a 12v wire i could use for sure? Just frusterating... spent all day on the thing... this is why i stay away from wiring!

JohnCalvin

ok.... i've got the 12v on the back on the ignition switch... but still nothing happens! Black to a ground, green to the negative on the msd blaster 2 and the red to the back of the ignition!!! Thoughts, ideas, comments????

JohnCalvin

Sooo... just to recap: in the last month i have:

Built a roller 302
Removed and tore down the old 289
Dropped in the new 302 and tuned it
New stainless steel 3/8 fuel line
620 mustang plus front suspension (springs, shocks, sway bar, etc.)
New 1 piece export brace

all done by me in my garage... and the thing that is going to do me in and be forced to drive to a shop and pay them 90 an hour to do is a stupid tach?!?!?! Guess i can't hook up 3 wires correctly! UGH Nevermind my rant....

JamesW

Tell use exactly where you have all 4wires connected....

this is typical:

Tachometer Wiring:
Red to 12-volt "switched" power supply
Black to ground
Green to trigger (negative side of coil, or tach output terminal if using an aftermarket ignition control)
White (or yellow) to light circuit

JohnCalvin

Green wire is connected to the negative side of my msd blaster 2 coil
Black wire is grounded to the same ground as my alarm
Red wire is connected to the threading on the back of the ignition... which i was told was a 12v source... I also tried splicing that into several other places with out any success...
White wire is not connected to anything... i figured i'd try to get it working before i worried about the light. I did ground it out though just incase that not being connected would make a difference.... it didn't... :-(

gothand

Try hooking your green wire to the tach output on the MSD box. It will probably not work as most do not. If it doesn't work then you need an MSD 8920 tach adaptor (assuming you are using a magnetic pickup dizzy). It will work for both current and voltage triggered tachs.

http://store.summitracing.com/partde...p;autoview=sku

If you don't want to deal with the tach adaptor you can get a nice Autometer gauge which will work off of the tach terminal on the 6AL.

Good luck!
Jeff

adr3naline

I have a similar question about which wires to connect too. I'm attaching my wiring diagram for a 70. In my chilton manual, I'm guessing I need to connect to the wires that I have highlighted. At the light switch, it would be the red/yellow wire. At the ignition, it would be the pink wire (in the Chilton, it says Pink or Red/Green).

I'm attaching my diagrams with highlighted wires, so you can either confirm the wires I have selected, or help me figure out which ones I should connect too. I really appreciate your help!

bluovalguy

On your fuse box, there is a fuse marked ACCY. Splice the red wire onto this wire. That will give it power only when the car is started. I bought a Summit tach and that is the wire I used, no problems at all. As for the white wire to control the lights, just splice it into one of the dash light wires. Then it will only have power when you turn on your dash lights.