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I literally just did this exact install yesterday on my 1978 F250 and followed the same basic wiring. I have a 1984 351W in the truck, so I just tapped into the Tach Test wire in the harness. I also found a switched 12V source as well. The one thing that I didn't do right was I tapped into the headlight wiring harness for the light on the tach, except the light only works when I put the lights on and when I switch to high-beams, I lose light. I am going back into the harness to find the instrument panel lights.
I literally just did this exact install yesterday on my 1978 F250 and followed the same basic wiring. I have a 1984 351W in the truck, so I just tapped into the Tach Test wire in the harness. I also found a switched 12V source as well. The one thing that I didn't do right was I tapped into the headlight wiring harness for the light on the tach, except the light only works when I put the lights on and when I switch to high-beams, I lose light. I am going back into the harness to find the instrument panel lights.
Frank
Tie into the wiring for the bulb that is on the left of the dash panel that lights up the display for the lights and windshield wipers. Very easy to find.
x2 on the bulb for behind the windshield wiper/headlight switch for the white wire for the lights.
I don't agree on the red wire though. For that one, there is a yellow harness that hangs in the dash behind the headlight switch. It is a 12v switched, and you can connect to it with a bullet connector on your red wire. Don't mess with the wires that lead to the tumbler if you can help it.
No problem! This is what it looks like. It's the yellow harness with 3 female bullet connectors. It has a black wire with a green stripe going into it. In this picture, my red gauge wire is coming out of it.
Thank you for that picture. I will make sure to tap into that wire. Is this connection just hanging around? Can i use this for more than one 12v source since it looks like it has three outputs?
Last edited by puroford; Jul 13, 2011 at 02:23 PM.
Reason: added words to clear up the statement
Not sure if I understand yer question but on the DSII, a green/white stripe wire goes to the TACH TEST horseshoe connection on the coil.....from the loom. The distributor has a three wire connection - orange, purple and black
Not sure if I understand yer question but on the DSII, a green/white stripe wire goes to the TACH TEST horseshoe connection on the coil.....from the loom. The distributor has a three wire connection - orange, purple and black
I don't know why I said distributor in my last post. I mean the wire that goes to the coil. Wondering is someone has a picture of where this wire splices in?
If you're looking to hook up a tach...(as the thread title suggests)...you can wire the tach to the neg (-) connection on the coil.
If you're looking for where the G/w wire splices into the loom from the coil, give me a few and I'll go look at an old (haha) harness....but I think it runs into the ICM and another 4 prong plug harness....
Can't give you a picture...but - the G/w 16 ga wire from the coil's TACH TEST runs into the loom that houses the oil sending unit wire (and some others)......over to the ICM area. The ICM has a rectangular connection - R/g, R/w, etc and next to that is a circular 4 connection dealie. The 16ga G/w wire connects opposite to a solid, light Green, 18 ga wire.....then runs into the cab. From there.........?