Brown wire fix routing

[V12StealthHunter]

After lots of troubleshooting I've somewhat narrowed down the starting issue I have to the brown wire.

The voltage on the battery is 12.32v and the voltage on the thick black wire going to 30/1 on the ignition switch is also exactly 12.32v - so no drop from the battery. But the brown wire read 11.66v. That's almost a 1v drop. This reduced voltage seems to be insufficient to actuate the starter solenoid. The solenoid needs at least 12v. Given that the black wire and brown wire physically attach themselves together with the +ve Battery connection on the starter stud I can only assume the 1v drop is between the starter and the ignition switch. But according to the wiring diagrams there is nothing between those two points for the brown wire. So I don't understand why there is a 1v drop on the brown wire when the black wire it shares the loom with has a 0v drop (I've obviously cleaned all the terminals with a metal file till they were all nice and shiny).

In any case I decided its probably time to run a clean 10 gauge wire to the ignition switch from the starter, i.e. the "brown wire fix". I followed the existing wire and found that it goes into the firewall just under the two brake fluid reservoirs. There is simply no space for an extra wire through that grommet. So I googled to see how people routed it but didn't find anything. Most posts were about taking a wire from the trunk (I'm assuming later cars had a battery in the trunk?). So that was no help.

More googling and I found that someone else also noted that there was no space for an extra wire; http://archive.mirafiori.com/show.php?fid=2&msg=144957

Today I wanted to finish my brown wire fix. Went to look for a opening in the
firewall to feed the new wire. Wow these Fiat's are sealed well. The existing
wiring harness routes are packed.

That chap eventually drilled a new hole. I absolutely hate making modifications like that. Any suggestions on how to route the new wire on a 1971 car?

thanks.

[paintdudeluke]

If you want it to look factory, enlarge the original hole and use a bigger grommet.

[aj81spider]

A quick look at the wiring diagram seems to show that the black wire actually ties to the alternator and the brown ties to the starter stud. The black appears to go directly to the ingnition switch without going through any connectors (on the 71 wiring diagram I have), and the brown goes through one connector. My guess is that the connector is the source of your voltage drop.

That doesn't answer your question (how to route the wire), but it may give an alternative to putting a wire in.

I'm not familiar with a 71, but on my 74 there are several penetrations of the firewall. Were I to route a wire I would just pick a different one to come through. Drilling a hole isn't the end of the world, but make sure you use a grommet if you do. Otherwise the vibrations will eventually cut the insulation and you will short the wire to ground. There's a lot of current and no fuse on that wire so very bad things will happen.

[TStark]

I concur
My 75 had a 4 pole quick disconnect about 12" from the starter, that looked factory.
I
So basically the entire car was powered though a a spade terminal.
I suspect that is where your drop is.
Also the starter solenoid wire was in the cluster, another unnecessary spade terminal pair.

Also, how I read the factory schematics, the brown wire will only power the headlamp circuit, but through the key switch. The rest of the car appears powered through the black wire, on a different pole of the key switch.

[Kevin1]

Just a suggestion, but it may be better in the long run to add a relay to supply voltage to the solenoid, taking the load off of your ignition switch. Also eliminates the need to run a wire through the grommet.

[V12StealthHunter]

A quick look at the wiring diagram seems to show that the black wire actually ties to the alternator and the brown ties to the starter stud. The black appears to go directly to the ingnition switch without going through any connectors (on the 71 wiring diagram I have), and the brown goes through one connector. My guess is that the connector is the source of your voltage drop..

Which wiring diagram are you using? I've looked at the big paper fold out wiring diagram that came with the user manual and it doesn't show any connectors in brown wire's path. But now I seem to recall there might be a big 3 cable white plug next to the carburettor that connects the Red, Brown and Black from #50 and #30 on the Starter to the wiring harness. I'll need to go check that today.

The way I've interpreted the wiring diagram is as follows;
- Black wire goes from +ve Battery to Alternator to Starter (#30) to Ignition Switch (#30/1)
- Brown wire goes from Starter (#30) to Ignition Switch (#30)

Electrically the two should be the same

I have noticed there is another hole in the firewall with a rubber spigot in it. If I were to guess, I think that has something to do with the HVAC system. Some sort of drain? Its next the the carburettor.

[aj81spider]

I have a wiring diagram set that Brad Artigue put together. It's a PDF, so PM me your email and I'll send it over.

[majicwrench]

"somewhat narrowed down starting issue" is kinda vague. What starting issue?? If you dislike modifying, figure out problem (not just "somewhat") before adding new wires or drilling holes. My 72 starts runs lights work well without any infamous brown wire fix.
And 12.32 volts at battery is NOT a fully charged battery, which should be 12.6 volts. Start w a charged battery.

When checking volt drop, you will not see a drop till the circuit is loaded. Any wire has resistance, if circuit was loaded (key things on) dang near impossible for yo to have 12.32 at battery AND at ign switch. Proper testing will prevent all sort of unneccessary repairs (like adding more wires)

Again, what sort of starting problem?? This is a very simple car and electrical system.
Keith

[V12StealthHunter]

Again, what sort of starting problem?? This is a very simple car and electrical system.

Exactly. This is why its puzzling. I don't know what the problem is, that's why I'm here. But I know what the symptoms/side effects are, which is the no start due to lack of power to starter solenoid. The 11.6v from the brown wire is not enough to actuate the starter solenoid. If I simply swap the brown wire with the black wire (12.3v), i.e have the black wire feed the starter solenoid and use the brown wire for fuse #9 plus ignition coil, the car starts up instantly and runs fine - "fully charged" battery or not.

I plan to move everything neatly onto relays one day but not immediately. For now I just want to determine whats causing the voltage drop on the brown wire and fix that or find a good location in the firewall to run a second brown wire.

[majicwrench]

Nice to know what the car in doing, not cranking due to lack of power at brown wire at starter. That is much better description than "starting issue", thank you
Finding a volt drop is simply a matter of working your way along the wires/connections/switches w circuit loaded till you find the drop. Arrange some sort of bungie cord/vise grips contraption to hold key in crank position. Car will not crank, correct?? But circuit is now loaded, current is trying to energize soleniod. Now start checking voltage. If voltage at battery is 12.4 v (just for example) and voltage at key switch is 11.8, you have a problem tween the two. If volt is 12.3 (lets say) going into ign switch, and 11.8 coming out, you have a problem in switch. Which sounds like the case here. Any wire, switch, connection will have some volt drop, but it should be very slight, not .5 volts.

[V12StealthHunter]

In the clarity of day light I found a perfect route for the brown wire. On my car, just beside the main loop grommet there was a rubber blank over a hole. It looks factory because the rubber has deteriorated badly. I just put the wire through it and routed it exactly like the old brown wire.

I've just disconnected the old brown wire altogether. I don't understand what's wrong with it (voltage drop) so I've left it unplugged until I have time to look at it again. For now the new 10 gauge wire seems to be doing the trick just fine.