Brown Wire Mod on my 1978...

zonker

zonker

Just Another FIAT Freak
I've been reading and researching many of the posts here regarding BWM, but for some reason I am having to fill in the gaps a great deal in order to apply the offered up knowledge to my 1978.

My confusion and condundrum lies with the fuse 10 and fuse 12 locations always being referred to. According to my original owners manual (and to the fuse box markings), fuse 10 ( letter L) is a long 16 amp fuse for the radiator fan and the horn. Fuse 12 is a short 3 amp fuse protecting the headlight raising relay.

Here is a breakdown of my fuses, and the panel cover's markings that mimics the owners manual:

A - 1: (12v switched, 8A) brake lamps, turn signals, oil light, temp gauge, fuel gauge, brake indicator lamp, back up lights, seat belt light/buzzer, rear defroster, heater fan, winshield wipers, winshield washer, tach, voltmeter, and factory radio.
B - 2: (12V direct, 8A) headlight motors, remove key buzzer, carb fan, dome light
C - 3: (12V switched, 8A) left hi beam, hi beam indicator
D - 4: (12V switched, 8A) right hi beam
E - 5: (12V switched, 8A) left low beam
F - 6: (12V switched, 8A) right low beam
G - 7: (12V switched, 8A) frt left / right rear side markers, park/tail lamp indicators, right tail lamp, left lic. lamp, ideogram fiber optic bulb, front left park lamp, cigar lighter light, heater ideogram illumination
H - 8: (12V direct, 8A) front rt parking lamp, left rear tail lamp, front right and left rear side marker lights, right lic. plate lamp
I - 9: (12V direct, 16A) hazard lights and indicator, cigar lighter, rear defogger
L - 10: (12V direct, 16A) radiator fan and relay, horn and relay
M - 11: (12V direct, 3A) headlight conceal relay
N - 12: (12V direct, 3A) headlight raise relay

So... according to what I have listed above, which 12V direct line do I tap into, and how will that actually help the voltage load of the switched accessories? I'm getting the feeling that the early pre '79 X1/9 fuse locations do not match the later models..

UPDATE:
After studying the wiring harness manual, it appears that on my '78, fuses #10 and #12 are not the ones that need the BWM, but rather fuses #10 and #2.
In addition, to cut down on ignition switch loads, I'll be adding a bosch 30A relay to power fuse #1 by using the existing power wire as the relay trigger on terminal 85, and new wires from battery to terminal 30, and terminal 51 to #1 on the fuse panel. Last but not least, terminal 86 will be grounded.

Sound like a good plan?
 
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In addition, the owners manual actually cites what the current draw is on the most power thirsty of the accessories. Here they are in order of current draw:

Starter: 800 watts
Headlights: 110 watts
Radiator Fan Motor: 55 watts (each)
Carburetor Fan Motor: 50 watts
Windshield Wiper Motor: 25 watts
HVAC blower motor: 20 watts
 
zonker said:
In addition, the owners manual actually cites what the current draw is on the most power thirsty of the accessories. Here they are in order of current draw:

Starter: 800 watts
Headlights: 110 watts
Radiator Fan Motor: 55 watts (each)
Carburetor Fan Motor: 50 watts
Windshield Wiper Motor: 25 watts
HVAC blower motor: 20 watts
Click to expand...

Regardless of the BWM, I would make sure those are ALL on a relay (except starter). I am pretty sure Radiator fan is, but I know headlights are not and neither are wiper motor. Don't know about HVAC or carb fan motor.
 
Thanks... I will do that eventually. Right now it's all about parts with reduced loads and the BWM first.

For my 800 watt starter condundrum, I bought the new gear reduction unit that Allison sells. I believe it has a lower amp draw than the oem starter. It surely is lighter and spins the car over faster.

The headlight bulbs have been replaced with LED units and the draw on them is around 2 x 7W total. I think I need brighter bulbs though, so this is not the final answer yet. Looking at the 2 x 15W units.

As for the BWM, I chose to add the new wire to terminal 10, which supplies direct current to both fuses 9 and 10. From there, I re-routed terminal 10's original black and white wire combo to terminal 2, because of the larger gauge black wire would offer up less resistance than the skinny white wire connected on terminal 2.

That left me terminal 2's double white wires disconnected, and a great source for tapping current to feed my new spare tire mount subwoofer. I put a male spade terminal on the power lead from the sub and connected it there. Man, did that make a difference on the sound quality of my stereo!
 
Some more revelations and observations...

On my X, there was a black wire going to the power side of terminal 9 on the fuse box. According to the wiring diagrams in the factory book, terminal 9 is linked to terminal 10 so all it is is a power tap for another circuit if need be.

To confirm this, I checked the black wire individually for power and there was none, telling me this was drawing from the #10 power side hot wire. Figuring it was a factory install, it had to be for the A/C system, which is now defunct.

So last night, before buttoning it all up, I disconnected the black wire and went about my merry way. Tonight I did a little research and found this mystery black wire is the main power feed for the second radiator fan! I guess I need to hook the wire back up to make the second rad fan operable. Oops lol.

This tells me that after reconnecting the mystery black wire, my new BWM wire is exclusively feeding current to the following accessories:
Rad Fan 1
Rad fan 2
Horn
Hazards
Cigar Lighter
Rear Defogger

Now the items listed above carry their current thru 2 16A fuses and an 8A fuse, totalling 40 amps. I put a 25A ATO fuse on my new BWM wire. It has not blown a 25A fuse yet, but then again I have not added that second radiator fan to the mix.

My question is this... Did I put too light a fuse om my BWM wire? I'm gonna reconnect the black wire and see if I start blowing 25A fuses. I know it's an easy thing to check because when the fuse blows, the horn stops working :)
 
zonker said:
I put a 25A ATO fuse on my new BWM wire
Click to expand...

The "conventional" BWM does not use a fuse. Most implementations of the BWM is supplementing the existing (unfused) feed from the battery to the fuse box with an additional feed wire to reduce resistance (and thus voltage drop). Your setup could be different.
 
To me the fuse is a failsafe for my modification. I'm addition, its a nice way to gauge how much current i have diverted from the brown wire. For example, i had a 15 ammo fuse connected to it originally and i blew that one when i attempted to use all circuits attached to it, so i upped it to 20 and it did not blow. So for a margin of error i added a 25 and put spares in the glove box :)
If i start to blow that one after i reconnect the second cooling fan them ill up it to 30A. If I blow a 30, then i need to redistribute some of the power off my new wire, or think about adding lower draw cooling fans.

Rob
 
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