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I'm adding some aftermarket gauges (tach, oil pressure, temp, etc) and need two sources of power: switched power (i.e. only on when ignition is on) and power that connects to the dash lighting circuit. Is there any way I can do this through the fuse box without splicing wires? I want this to look clean and professional (and safe!). I've seen these add-a-fuse products that I might try. Would I put the add-a-fuse into the fuse slot that my dash lights work from, and another to a switched power source or do I need to use them in otherwise un-used slots? Are there certain auxiliary slots that give me switched power vs. all the time? Wiring is definitely not my strong suit, but I want to get it figured out on my own and avoid taking it in if possible.
One of those little add a fuse links stuck into the fuse panel is fine.
You need to tie into the dash lights after the headlight switch. The fuse panel is constant HOT source only. It does not turn on/off with headlight switch.
You could find a wire going to the lights and use this: scotch lok
to tie into the wire to get power from it. I am not super fond of them for long term use, but under the dash isn't bad. If you are not handy with soldering iron and shrink tubing this will suffice.
After some YouTube research, it looks like some vehicles have certain fuses that are always hot, others that are only hot when the ignition is on (i.e. fuel pump). I think I can do the add-a-fuse thing to fuse 17 & 18 to get dash and switched power respectively. Anybody disagree with that? Ideally, I'd like to figure out how to add a circuit to one of the "unused" spots in the fuse box, but the add-a-fuse is way simpler.
Follow-up questions. I wired up the tachometer last night and had no response when I started the truck. There are 4 wires:
Black = ground
Green = Neg terminal on coil
Red = Switched 12v power
White = dash lighting
I wrapped the black wire around one of the steering column bolts that holds it in place. Green is wrapped with the negative coil wire, which was then wrapped around the negative coil post. Since the truck started, I assume that connection is good. Red wire was added to spot # 18 in the fuse box with an add-a-fuse, and white was spliced onto the actual fuse in spot #17 since I accidentally bought two different size add-a-fuses and only had one that would work.
Is it possible the bolt in the steering column is not providing ground? I don't have light to the bezel or any reading on the tach when then engine runs. The whole gauge seems dead.
The ground would be the first check. You have to watch as there is so much plastic and things that are isolated from true ground on these trucks. Since nothing works(including the light) then I would think the ground is the issue.
Leave the key on, then move the ground to something else and see if the light comes on. That will tell you that it is now working.
I'll give that a try and report back. Now that I've thought about it a little more, I remembered that I had a tough time getting my horn button to ground. I had to run a wire from the center nut down to the firewall. I think we have a good lead on the issue.
I established a good ground connection and the dash lighting works quite nicely. The tach lights up when I turn on the dash lights. Unfortunately, the tach itself does not register any signal from the engine while running. I have a dwell-style tachometer for tune-ups that I connect to the negative coil terminal and a ground, and that works fine. When I hook up my column-mounted tach the same way, I get nothing.
Can anybody explain the difference between a dwell style tach with two wires, and the aftermarket type that requires a power source? Is it possible something crazy has happened like I've reversed positive and negative wires on my coil while sleepwalking?
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