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In-line fuse/fuse block question.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by heavy4x4, Jan 4, 2003.

  1. heavy4x4

    heavy4x4 1/2 ton status

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    Well, I just installed an Autogage tachometer...and it's working great. My question is, the directions say to use a 12V power source from the fuse block, or use an inline fuse. I didn't do either...yet. I was going to go into the fuse block because that seems like a good idea, but I don't have any of the odd shaped plugs that fit into the openings. Where can I get them? Do autoparts stores carry them? I probably won't go back and re-do it all, but I do want to install an in-line fuse. (I tapped into a 12V, ~18 gauge, wire off of the alternator) But, the directions don't say what amp to use. I bought 30's. Will those be good? Too high? Too low?
    Thanks for any help.
     
  2. Skigirl

    Skigirl 1/2 ton status

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    Just guessing here, but 30 is probably too high. If you call the manufacturer, they will give you how many amps it pulls. But definitely put an inline fuse in there right away. I never run anything that I don't fuse (or circuit break). Too much chance of fire without it. I like running inline because it gives you a clear path to look if you run into electrical problems down the road, as opposed to going thru the fuse panel. Personal preference I guess.
     
  3. HarryH3

    HarryH3 1 ton status Author

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    Yep, an 18 gauge wire will melt before a 30 amp fuse will. /forums/images/graemlins/shocked.gif The problem with that is that the entire wire will get red hot, like the heating element in an electric heater. /forums/images/graemlins/eek.gif I'd guess that a 2 or 3 amp fuse would be plenty for a tach. I also wouldn't tap into the control circuit for the alternator. A problem in the tach circuit could make the alternator stop working. /forums/images/graemlins/frown.gif

    Look closely at your fuse panel. There are usually a couple of available accessory taps. I think that some trucks even had a tap near the top of the fuse panel that the optional factory tach plugged into for power. It's been a long time, but I seem to recall that the factory tach on my '77 got it's power that way. /forums/images/graemlins/confused.gif
     
  4. heavy4x4

    heavy4x4 1/2 ton status

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    Thanks for the reply...I really wasn't sure what amp to use, so I bought 30's because I've blown those before when connecting my reverse lights to the battery. I guess I'll return them and buy some 3's or 5's. I also e-mailed autometer to see what they recommend.

    I was looking at my fuse panel for a place to plug in...and there are plenty. It looks like a really convienient thing...areas for ignition, 12 volt sources, etc. But my problem is, there are no un-used plugs (plugs, not places to put them) to attach the wires to. (Does that make sense?) They are a really wierd shaped connector that I don't have any of. Any idea where to get these?
     
  5. HarryH3

    HarryH3 1 ton status Author

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    I've always found junkyards to be a great place to find unusual plugs. I just snip off a few when I'm in a yard and add them to the junk box at home. /forums/images/graemlins/shocked.gif I've also seen adapters that plug into the fuse box with one of the existing fuses and provide a standard spade lug connection for the circuit.
     
  6. heavy4x4

    heavy4x4 1/2 ton status

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    I just put a 3 amp fuse in-line to the gauge, and all is well. Thanks.
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    You sure it say's to go to a "12V power source" and not to go to "12V SWITCHED power source"?
    Tach should not need power when the key is off. It might cause a battery drain if it power with the key off.
    As to where to connect. There are doezens of spade connections in the top of the fuse box. There is a colum Marked BATT, ACC, IGN. I can't remeber if they are male or female spades that you need. I want to say Female.
    Tachs do not need much power. 5 amp fuse should be plenty.
     
  8. heavy4x4

    heavy4x4 1/2 ton status

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    You bring up a good point. It does say 12V switched power...but the one I chose doesn't do anything until the key is turned to the on position. I also don't think (key word: think) that it's draining the battery. I've got both the gauge light and gauge power coming from the same source...and the light isn't on when my truck is off. So, does this mean my power source is okay? Not going to drain battery? The one thing that does kind of worry me...is that my gauge doesn't return to zero when the truck is off. When it came to me in the box...it was at 1100 rpm, and that's where it goes everytime I turn off my engine. (It does read proper rpm though when driving...it's not 1100rpm off)
    About the fuse box...when I looked at it...it didn't look like it had any common spade terminal "outlets." Maybe I'll look again, but I think all it has is the really weird shaped plug openings. (Man, they stuff that fuse box up under the dash...I can hardly see all of it...let alone get my hand up there /forums/images/graemlins/frown.gif)
     
  9. HarryH3

    HarryH3 1 ton status Author

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    Sounds like you have it connected to switched power. That means that the tach will only get 12 volts when the key is on. /forums/images/graemlins/cool.gif

    I would wire the tach light wire into the feed for the dash lights. This does two things. The tach light will only be on when the dash lights are on and it will dim with the dash light control. /forums/images/graemlins/thumb.gif
     
  10. heavy4x4

    heavy4x4 1/2 ton status

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    Good to hear.

    Ok, so what wire do I tap into. Anybody have a color and location for a dash lighting wire? I'd be happy to do that. (It's just so much easier to connect the light and power wire all into one /forums/images/graemlins/grin.gif /forums/images/graemlins/smirk.gif)
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Typically things are overfused/protected to about double their capacity, however, tapping into existing wiring is doing just that, going over the specified (by GM) rating of the wires that pre-existed. Most of the fuse panel accesory ports are protected via the 30 amp top most circuit breaker (about the center of the fuse panel) this can be changed with a 10 or 20 amp breaker available at almost all chain auto parts stores. If the wire goes to ground, no matter the diameter, it will blow even a 30 amp fuse before anything melts FWIW.

    Sounds tempting to wire into the headlight wiring, I've always found it to be easier/cleaner/more reliable to go to the wrecking yard and just get the right fuse panel plug and solder it to whatever you want to run. Dimming is overrated, enough so that early digital GM radios in Cadillacs weren't setup this way. You don't hear of many people wanting dimmer gauge lighting /forums/images/graemlins/smile.gif
     
  12. HarryH3

    HarryH3 1 ton status Author

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    </font><blockquote><font class="small">In reply to:</font><hr />
    You don't hear of many people wanting dimmer gauge lighting

    [/ QUOTE ] I hardly ever run mine past about half-bright. /forums/images/graemlins/shocked.gif I don't need to light up the interior of the truck, just the gauges. /forums/images/graemlins/wink.gif
     
  13. HarryH3

    HarryH3 1 ton status Author

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    </font><blockquote><font class="small">In reply to:</font><hr />
    If the wire goes to ground, no matter the diameter, it will blow even a 30 amp fuse before anything melts FWIW.

    [/ QUOTE ] If a thin wire is very long, the resistance increase just from heating the wire can be enough to keep the current below the threshold of a 30 amp fuse. It only takes less than a half of an ohm of resistance to keep the current under 30 amps. Meanwhile the insulation is starting to melt from the wire... /forums/images/graemlins/frown.gif

    I've seen this happen in bigger applications as well. At one place I worked, we were installing some new systems that ran on 208v 3-phase power at 100+ amps per leg. Each run was about 60 feet from the breaker panel. One of the phases got shorted directly to the neutral wire, right at the equipment. The neutral wire melted before the 125 amp breaker ever knew anything had happened. /forums/images/graemlins/shocked.gif Luckily the wiring was all inside of conduit, under a raised computer floor, so it didn't set the place on fire. /forums/images/graemlins/blush.gif
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    Can't read any of my gauges at half bright in my car or my truck when its truly dark out, and especially at dusk/dawn. My eyes aren't that great, but they aren't that bad either. /forums/images/graemlins/smile.gif
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    yeah, but in our cases, longest stretch of wire is maybe 20ft, at 12-14v, and the most likely (but not only possibility) problem always seems to be short to ground. (those of you that do wiring on your trucks without disconnecting the battery know what I'm talking about : )

    However, I wouldn't set *MY* truck up like that. If wiring from the fuse panel, since you can get all the way down to 10 amps on the accessory terminals, it's dumb to run a 30 amp fuse or breaker for a wire designed for no more than 10, or perhaps less depending on what accessory you are talking about.

    Fires are certainly one thing that everyone is trying to prevent by protecting circuits, and GM fused them as they are for a reason. Lots of people get away with splicing in stuff, lots of people also have their vehcles burn to the ground.
     
  16. imiceman44

    imiceman44 1 ton status

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    The odd shape you see is just the plastic cover and locking tab for the spade.
    You can use any regular female spade, it will fit.
     
  17. heavy4x4

    heavy4x4 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    You can use any regular female spade

    [/ QUOTE ]

    Really?!?!?! I've got plenty of those laying around...I'll give that a try.

    Anyone know what color wire and location to tap into for dash lighting?
     

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