remote wire relay fuse

I have decided to install a SPDT Bosch relay to turn on additional devices with the remote wire from my head unit. I've looked at the relay diagram in the "calculators, charts, diagrams" section, and I plan on connecting 4 devices to the 30 pin relay output. Subwoofer amplifier, Microbypass for parking brake, power antenna, & the factory amplifier (will probably eventually switch to second aftermarket amp to power speakers instead of factory amp). Which wires do I need to fuse? Should I wire a 500ma fuse on the remote wire between the headunit and relay? Can I tap into the constant 12volt source from the stereo to power pin 87 on the relay, or do I need to run a dedicated wire to the fuse box? I don't have the sub amp yet, but the stereo is going to be a Pioneer avh-x4700bs in a 2001 Chevrolet Suburban. I would appreciate any info I could get. Thanks

I have a similar setup for my HU. Battery +12V via FUSE to HU Constant and relay 87. 30 to the HU's Switched input. 85 to GND and 86 to the HU's Remote output. (Okay, that's thru a diode because I have diode-connected on inputs from IGN & a manually switched +12V, but that's irrelevant.) So the HU when ON places +12V on its Remote output to turn on the relay. In my case that's to keep the HU on even after IGN is turned off. But in your case you'd connect #30 to your 4 targets. Your batt +12V to #87 cable needs to handle your max load/Amperage. The as close to the battery as practicable fuse is selected to protect downstream distribution - eg 30A if a 30A relay, else less if the cable has lesser rating - eg, 20A or 25A for a 25A cable. It should also protect the smallest wire from #30 to all (4) loads, but rather than use the same gauge cable (as the fuse to #87 cable) to all loads, short thinner cables from #30 to the next fuse may be short enough and physically protected enough to negate else minimise the risk of shorts & disasters. Keep in mind, if one is on, they are ALL on. I presume the "Microbypass for parking brake" is related to the other audio functions unless its fine to have all co-occurring with Remote on. A Remote on fuse else protection should be added to prevent its damage - ie, fuse Amperage equal to or less than the Remote on's rated Amperage. I think most Remotes are intended for hefty Remote relays and most seem to be rated for a minimum of 2A (check its specs!!), hence maybe a 1A fuse which should be ample for typical automotive relays.

So are you saying I should power #87 directly from the battery? The four loads that will be on the #30 output are all remote turn on wires, so the amperage coming from all 4 loads probably won't even equal 1 amp total. And if it is only 1 amp, couldn't I just tap into the 12v+ constant source coming from the headunit that is fused at 15 amps from the fuse box? The remote wire's rated amperage is only 300ma. Do they make fuses that small for vehicles? I have seen some agc fuses that low, but they all say 250 volts on them.

Nah - don't fuse it - if it blows, it blows. Use a relay with a coil current under 300mA and IMO add a 1N4004 or 4007 spike protection diode. Most automotive relays are 60 Ohms or higher - ie, <250mA. But I assumed ONE remote was to supply +12V to other loads. If you are powering other Remote ONs the relay need not be a high current relay. A transistor is another option.

So I shouldn't try and fuse the remote wire between the headunit and the relay? The relay I have has a coil current of 133mA What about the 12v+ source. Would I be fine tapping into the constant 12v+ wire of the head unit? Would I need to add a separate fuse? Thanks.

I wouldn't bother - IMO the chance of it protecting anything isn't worth the trouble - but otherwise a 200-250mA fuse. Being such low current, the HU's const +12V should be fine. If the existing fuse protects the wiring to the remotes, no additional fusing is necessary.

Ok. Thank you so much for your help.

Are you using the super tiny wire that came in a power wire kit? As long as your remote wire is larger in size than the wire you tapped for power you will not need a fuse. If your remote wire is smaller than the wire you tapped, and you value your vehicle, I would fuse it. The fuse is to protect your vehicle from an accidental short to ground.

So if I used a 14 gauge cable from my remote to relay, and an 18 gauge cable to tap into the constant, I should be fine? If I did decide to fuse the constant wire, how large should the fuse be. The 4 items coming off the #30 output won't even equal an 1 amp. Thanks

If any part of the wire you are adding is smaller in size than the wire you tapped for power, you need to put a fuse at the point that you tapped off the OEM wire. 1 amp 2 amp fuse is fine. You are not trying to protect the circuitry inside the amplifiers, you are trying to protect your vehicle against the wire getting pinched under a seat mount or the trim sills.