Fuse Box Wiring Query

Technical questions and Maintenance advice post in here please
Post Reply
Paulc
Posts: 1842
Joined: Mon Apr 14, 2008 5:58 pm
Location: London

Fuse Box Wiring Query

Post by Paulc »

New wiring loom in place and I have 4 green wires going to the A4 fuse (I didn't install the loom), but the wiring diagrams show 3 green wires to A4. The horn and fuel gauge don't work............could the additional wire be the clue? All the other connections to the fuse box are correct.
User avatar
gazza82
Site Admin
Posts: 5585
Joined: Sun Nov 24, 2013 3:39 pm
Committee Role: WebEditor
Location: Buckinghamshire
x 2
x 17
Contact:

Re: Fuse Box Wiring Query

Post by gazza82 »

I have the live side of the horn to A2 on my diagram (A35) (permanent live) - brown with green trace.

A4 (switched live) feeds flasher can (pole B), stop light switch and fuel gauge (B) - all green wires.
"If you're driving on the edge ... you're leaving too much room!"

Club WebEditor.

Cars: "Project 757" '59 A35 2-door bought in 1971 & Subaru BRZ SE LUX Auto plus "family fleet": Alfa MiTo, Peugeot 206, (Ex '98 Alfa Romeo 156 2.0 TS)
User avatar
Neil Evans
Posts: 12179
Joined: Tue Apr 15, 2008 1:06 am
Committee Role: Technical Officer
Location: Boston, Lincolnshire
x 11
x 25

Re: Fuse Box Wiring Query

Post by Neil Evans »

The horn and fuel gauge are fused from different sides of the fuse box so it's likely you have two faults...

The horn is easy to sort. It has a live feed (brown) direct to the horn from the fuse box that should be permanently live. The second wire goes to the steering column and eventually earths through the horn button.

Take a test light to 'brown' side of the fuse box and earth and it should light.

Take a test light from the brown wire on the horn terminals to earth and it should light.

Take a jump wire from the other horn terminal to earth, the horn should sound. If it doesn't the horn is faulty.

If it sounds, remove the steering wheel centre and short the link wire to earth, the horn should sound.

If it sounds, the fault is in the horn button. These often suffer corrosion on the terminals if not used regularly but the switch can be dismantled and the contacts cleaned.

If it doesn't, remove the steering wheel and short the sprung terminal on top of the light switch to earth, the horn should sound.

If it sounds the fault is in the slip ring on the steering wheel, or the short link wire. I've known the steering wheels be painted and the slip ring get a nice covering as well..

If it doesn't, there's a connection block where the switch wires join the main loom. Find the corresponding wire here and short that to earth. Could be a bad connection here...
Club Technical Information Officer
A30/A35 Club Member A191 (since 1972)

Father of the club's only love child
User avatar
Neil Evans
Posts: 12179
Joined: Tue Apr 15, 2008 1:06 am
Committee Role: Technical Officer
Location: Boston, Lincolnshire
x 11
x 25

Re: Fuse Box Wiring Query

Post by Neil Evans »

Fuel Gauge...

Remove the wire from the tank unit and short it to earth on the top of the tank unit. With the ignition on it should read 'full'.

If it doesn't, short the wire to the car body. If it now goes to 'full' it's that the tank is too well painted/undersealed and is not making contact with the body. Sometimes it's necessary to run a short earth lead from the body to the sender unit.

If it now reads full the sender unit is faulty.

If if the above doesn't get the gauge to read 'full' you'll need to pull the speedo out, then...

First check that the gauge is wired up correctly. There should be three or four green wires going to the terminal marked 'B' (battery) and a single green/purple to the 'T' terminal.

The multiple green wires should light a test lamp when the ignition is on. If the heater, wipers etc work it's almost certain this will be live as the feeds to these other components are the additional wires here.

Short the 'T' terminal to earth and the gauge should show 'full'. If it does, the fault is somewhere in the wiring to the rear. If it doesn't you have a faulty gauge...
Club Technical Information Officer
A30/A35 Club Member A191 (since 1972)

Father of the club's only love child
Paulc
Posts: 1842
Joined: Mon Apr 14, 2008 5:58 pm
Location: London

Re: Fuse Box Wiring Query

Post by Paulc »

Thanks all, off to the garage with your top tips.
Paulc
Posts: 1842
Joined: Mon Apr 14, 2008 5:58 pm
Location: London

Re: Fuse Box Wiring Query

Post by Paulc »

Well I tracked down the problem with the horn and it was a build up of paint on the slip ring (as Neil said). There is a problem with the windtone horn though, and even after cleaning the contacts it still doesn't work. I know it isn't the wiring as I tried an A30 horn and that worked. The fuel gauge still doesn't budge and I'll take the speedo out and try another.
Post Reply