Breva 1100 - faulty wiring causing ECU voltage reading?

[manos77]

Hello everyone,
Yesterday I encountered the cold start issue after a long time.

My situation is this:
- Battery is good and charged (12,5V on poles).
- Once a year I clean the ground points and fuse pins
- The relais starter kit is installed since years ago.
- Connecting directly the + battery pole to the started motor it fires up eagerly.


I notice that while the voltage on battery is 12,5V the ECU sees 11,6V, almost 1V less.

In 15 years I have replaced more than one cable of the shitty harness: the cable from ecu to lambda sond, from alternator to battery and a few other cables around the battery. All rotten.

What I suspect is that the cable giving power to the ECU is rotten, causing severe voltage drop.
The ECU gets powered directly from the battery through a 15A fuse in the auxiliary fuse box which is located under the seat.

Could this be the cause or am I out of track?

Any help would be precious

[Kev m]

I could be remembering wrong, but I seem to think that voltage drop was there from new on mine and others at the time.

[Bisbonian]

While probably not your problem, or maybe it is, 12.5 volts is not fully charged.

There are a bunch of different tables that talk about voltages and total state of charge, and it does depend on what type of battery you are using. But it looks like 12.5 volts is somewhere between just less than 90% and just less than 70% of fully charged (depending upon battery type).

Perhaps a good load test of your battery is in order.

[Wayne Orwig]

12.5V may be great if cold. May be low if warm.

As pointed out, a load test is a great start.

[SemperVee]

 The readout on my Norge (Breva with a fairing and more comprehensive dash) is ALWAYS LOWER then actual with voltage meter...

[pehayes]

You are going down a rabbit hole and will be chasing this forever.  You'll have total frustration.
Read all four pages of this link:
https://wildguzzi.com/forum/index.php?topic=117948.0

Now go install a bypass circuit and switch and be done with it.

Patrick Hayes
Fremont CA

[manos77]

Thanks everybody for replying.

Voltage drop has always been there indeed. But always around -0.3V. Never 1V...

I am pretty sure the harness is bunch of rotten hay straws
Last year I replaced the cable from the alternator to the battery. For the first time I got 14+ charging voltage on the battery!

For a start I just took the battery to my battery dealer for health checkup. Will come back for update

[Kev m]

It's been discussed here over the years.

Some have had success addressing the harness and/or grounds:

Dash voltage reading vs. at the battery... https://share.google/3RrFKzbrSLeTIlxEn


Some looked deeper at the circuits powering the dash and any other components that might affect the reading:

GuzziDiag Voltage reading - Norge question https://share.google/v20rM9kQfGv8bmKEk


Others just lived with it.