I have an early 99 where I'm going to add power and heated seats on both sides. I need a 15A source that comes on when the key turns on. Do I tap into a 15A wire at the cab junction box under the steering wheel for it, or wire it some other way ? I've read some that mention using a relay, but I'm not that familiar with how a relay works. I also need a 30A constant hot power source. Does that come directly from the battery with a 30A inline fuse ? Thanks.

 

I'm not much good on electrical either, but I would use a empty space in one of the fuse boxes, wire from there with new fuses installed. Someone should pop in soon with other ideas I'm sure.

Chet

 

The accessories you want to add require a relatively large amount of current. I would take power from the stud that supplies 12V to the under hood power distribution box (fuse box). Conenct a weatherproof in-line fuse holder with a 30A fuse for the source that needs to be hot all the time.

For the switched source you will need to use a relay. A relay is nothing more than a switch that closes when you apply power to it. A coil of wire inside the relay becomes a magnet when a small current is applied, and the magnetism pulls a larger set of switch contacts together. The idea is that you can switch a large current by supplying a small current to the relay coil.

For your application you will need to supply power to one side of the relay contacts through an in-line fuse holder, just like you used for your hot source (except fuse it at 15A). The load will be supplied by the other side of the relay contacts. The relay coil will need to be connected to a circuit that goes hot when the key is turned on. The beauty of using a relay is that you don't have to worry about overloading the circuit you tap, because the relay coil draws very little current. I would use a non-critical circuit such as the radio, and tap it at the fuse. The other end of the relay coil will need to be conected to ground.

All of the wiring, relays, fuse holders and connectors are available at most auto parts stores. A standard 30A 12V automotive relay (like the larger ford factory relays) will work fine.

Chris

 

Thanks Chris, that's a great help. I would attach a diagram that I've been looking at so I can pick your brain more, but the forum says I can't do that, so hopefully the link I attached will work. It's a diagram I'm using to wire some back-up lights soon, and seems it could apply, so I'm using it as an example. I'm also doing it so I can understand this relay issue. I take it most relays have the same 30/85/86/87 pin configurations. The diagram I'm looking at came from Susquehanna Motorsports.

Looking at the link (assuming it works) and based on what you described, the 30 pin would hold the wire with the 15A weatherproof in-line fuse coming from the battery. The 85 pin would go to the ground you said would be needed. The 86 pin would be the pin that the switched on power wire would be connected from/to. The 87 pin would be the wire that goes to the connector on the seat that needs that source. Do I have that right ?

How To Wire Your Auxiliary Lamps

For the junction box under the dash, there are various fuses that aren't used and/or come on with the key. Fuse 8 is the radio at 5A, 9 and 10 are not used, 16 is the instrument cluster at 15A, and 17, 18, and 21 are also empty. Assuming fuse 16 for the instruments would work, how would I tap into that, as in which side of the fuse pin ? Thanks.

 

Good find Lucca.

Chet

 

You have the wiring 100% correct. The numbers that your link refers to are pin numbers used by Bosch and have carried over to other companies that make compatible replacement relays. Some relays will have a fifth contact labeled 87a which you don't need to use.

There are a number of ways to tap into the circuit. The best way is to use a fuse tap that has a separate dual fuse holder and attached wire pigtail. They use 2 fuses, one to protect the factory equipment and one for the aftermarket stuff (your relay). You can find them here:

http://order.waytekwire.com/productd...CIRCUIT%20TAP/.

When you install the fuse tap, make sure that the aftermarket equipment is supplied by the hot side of the factory fuse contact. You can tell which side is hot by pulling the factory fuse, turning on the ignition, and checking the contact for each leg with a volt meter or test light. The reason for connecting to the hot side is so that the current drawn by the additional equipment isn't added to the factory fuse, but instead is carried by the new fuse. You won't need more than an a 3A fuse going to the relay coil.

The same website above has all of the wiring components you will need to complete the job. Keep the length of wire between the +12V stud and the in-line fuse holders as short as possible. Install the relay where it won't get hot or wet.

Chris

 

Looking at that fuse tap with the 2 fuses, I assume the instructions would show which fuse is for the factory part, and which fuse is for the aftermarket ? The other thing, in looking at that Waytek fuse tap, is what if there is no room to insert that tap ? In looking at it, the 2 fuses are at 90 degress to the pins that will be inserted into the fuse box, and if the angle won't allow me to slide the base fuse pins into it, how could I get around that (I'm assuming I would go into my #16 slot, which is the instrument cluster fuse location) ? Could I try the empty fuse slots and test them like you mention ?

If none of that works, what about sliding this (Motormite/Blade fuse taps (85606) | Fuse and Accessories | AutoZone.com) over one of the pins at the #16 fuse ?

 

The 2-fuse tap should be labeled, but if not it should be pretty obvious by the position of the wire pigtail which fuse does what. If there isn't room, the blade fuse taps will work too, but they tend to spread the contacts in the fuse box and require an additional in-line fuse to the relay coil. If you use the blade type fuse tap be sure to still connect it to the hot side of the factory fuse.

You can definitely use the empty fuse positions if you like. Test them to make sure one side goes hot when the key is turned on and use a narrow flat tab crimp connector to make the connection. You will need to use an in-line fuse to in this configuration as well.

Chris

 

Let me describe something else I just thought about. Here is the wiring set for the drivers seat:

white/red stripe (upper left) - power/hot
brown/light blue stripe - seat belt indicator
green - power/hot
black - ground
red/black stripe (lower left) - heat voltage thru 30A fuse
light blue/red stripe - heat in run with 15A fuse

The red/black stripe we talked about coming from the battery using the 30A in-line fuse. The light blue/red stripe we talked about using the fuse tap (I've since found one, but haven't tested the fuses yet for a switched on source).

The other issue I hadn't thought about was the passenger side seat that will need power, but only has these 3 wires:

black with white tracer - power
black - ground
white/red stripe - hot all the time

I think the black/white tracer is a 30A power requirements, which I could do from the battery using another in-line fuse (?). The black is the ground, which is easy. But the part I just thought about is the white/red stripe wire. That wire exists with both the drivers side seat and the passenger side seat. Is it doable to have another relay for that seat (it will have it's own wiring anyway at least for the 30A power), and have the dual 87 pins (87 and 87a), where one of the 87 pins goes to the drivers side seat and the 87a going to the passenger side ? I've seen where that would need a 20A fuse, so it seems it would be the 20A in-line fuse close to the battery and connected to the 30 pin, the 85 pin to ground, the 86 pin wouldn't be used (?), and the 87 and 87a would go to both seats ?

 

If the white/red wire is powered all the time (as your list says) then you don't need a relay. Just add another in-line fuse holder at your power source and use it to supply the white/red wire. You only need a relay to energize the circuits that need power when the ignition is turned on.

Don't use pin 87a in place of pin 87. 87a is the other side of a single pole double throw relay contact, which means that it will operate opposite to 87. In other words, pin 87 gets power when the relay is energized and pin 87a loses power when it is energized.

Chris

 

Can the in-line fuse be split into 2 lines ?

 

Yes it can, but the single fuse will then be supplying both seats, and you will need a fuse with twice the required current rating. This offers less protection than using two individual fuses, one for each seat.

 

In looking at some of my notes, I have a hunch the white/red tracer wire I'm asking about now might be a switched on power source. If that's the case, I would need a relay for that as well as the 15A we already discussed. Or 2 relays, one for each wire for each seat and keep them separate ? It's getting crowded under the hood finding spots to put relays !

The other thing is I did some testing of the fuses last night to try and find a switched-on power source. The only fuses there are it seems are the max fuses in the power distribution box under the hood as well as some mini fuses in one area, and those ATM mini fuses. And the fuses that aren't used at the box inside the cab don't have the wires going into them to test. I think I found one inside the cab I can tap into for the first 15A we talked about, but now if I do those dual 20A's, what's a way to do that ? And I was having a hard time finding one of those taps you mentioned above 10A.

 

The relays you are using are good for 30A, so you only need to add one if the two additional 15A loads need to be switched with the ignition. Put a 30A fuse between the power stud and relay pin 30 and then two 15A fuses coming from pin 87 to your loads. You only need to find one switched power point in the fuse box, it can be used to power multiple relay coils.

Chris

 

Chris, I'm sending you an e-mail thru the website.