Tach hookup question

[KeepOnTruckin390]

So, I got a standard Bosch 4 wire tachometer to mount on the steering column. I have a 1970 F100 which I believe is the only year that they used the circuitry panel for the guage cluster lights. I would like to splice the tach light wire into the guage lights wiring so it dims and brightens with the dimmer sweep on the light switch. I can't really tell very well from the wiring diagram which wire I should splice into or where. From what I have found, there is a blue wire with a red stripe that goes into the pigtail that plugs into the back of the guage cluster and that would be the one. I just wanted to make sure though before I did it and see if anyone had any concrete experience with this that might be able to help a bit. Thanks

Branden

[Ranchero50]

Blue and red is the dim able interior lamps if memory serves. You should be able to find unused plugs for the lamps and power. You will need to drag a coil negative back to the cab.

[KeepOnTruckin390]

Ok thanks. Yeah the green wire on the tach I believe goes to the neg side of coil, then the black and red are power and ground, but the white tach wire is for the light inside the tach and just wanted to make sure I spliced it into the correct wire for dimmable lighting. So, are you saying that I should be able to find an unused wire for the lighting? rather than splicing? Thanks again

[Ranchero50]

Yes, pick one of the bullet connectors for the lamps (heater or radi0 work well) and make a 'T' wire out of your tach light wire. Have one male and one female pullet connector. That way you can just plug the tach lamp wire between the chassis wiring and the heater lamp (for example). Keeps the chassis wiring in better shape vs cutting it up.

[KeepOnTruckin390]

Ok, thats interesting because it raises another question. I don't have any lighting on the heater controls right now. Should I? I also have a random bulb and socket that the PO draped over the glove box but doesn't look like it goes there. I wonder then if that is the heater control light that the PO for whatever reason draped over the glove box opening. Thanks again

Branden

[KeepOnTruckin390]

Well for now, I just stuck the wire in with the 2A fuse for the instrument panel. I will mess with it later when I replace the dash bezel and what not. Still curious about the heater control light though if anyone has any knowledge on that. Thanks

[Ranchero50]

Yep, heater control should have a bulb with a spring clip (looks like a flower) for the base that'll pop into the back or top of the casting. Real PITA to get it in and I think there's supposed to be a little metal clip that keeps the wire out of the control cables way.

[KeepOnTruckin390]

Awesome. Thanks sir. I will bet money that's the one the PO has setting on top the glove box insert because it looks just how you explained it, with "prongs" or whatever that would hold it into a hole, but can't seem to see where it actually belonged. Also explains why I can't see the heater controls at night Oh well, Good to know because I haven't had the truck very long and am going through fixing stupid little things just like that Thanks again

Branden

[KeepOnTruckin390]

Update. The misplaced light was in fact the light that was supposed to go into the heater control. It is now back in it's spot and works. Thanks for helping clear up both of those myteries. i.e. random glovebox bulb and no lights in the heater control