Wiring the MGA... help

Wiring is certainly not a strong point for me.. I put juice (12 volts at 10 amps from a battery charger..per Mr. Gaylord suggestion) to the harness tonight for the first time, and the only thing that seems to work right is the fuel pump, the starter and the horns, everything else is nada. I assume this has something to do with the mess of red wires that go into the light switch..but the wipers don't work either. Should the starter crank with the key off?

David,

First, the starter should crank with the key off.

The horns effectively work direct from the battery via fuse and push switch.

However, the fuel pump is powered through the ignition switch. You should also have 12v at the coil and ignition warning light should light.

Now you need to check if you are getting 12v through the brown and blue wire to the light switch.

Pretty much everything else is powered from the green wires out of the fusebox so check that fuse! (the fuel pump is powered through the unfused side of the same)

Now check through the system carefully with the wiring diagram and a test lamp paying particular attention to connectors and earth points.

Please report back as you go!

David,

Is the wiring loom in your A the original or have you re-wired?

I have recently done a frame off on my MGA 1500 that included a complete re-wire with a harness purchased from Moss.... It has worked out well with a few minor problems that I was able to correct with a little patience and perseverence...



The re-wiring is pretty straight forward as long as you have a wiring diagram. The web-site http://www.mgaguru.com/ has a very good selection of color coded specific area diagrams that may help you figure out what is going on regardless of new or old wiring.

Hi Ron,

new harness from British Wiring... putting in the head liner tonight... woo whoo

See here: http://mgaguru.com/mgtech/electric/circ_a.htm

If the fuel pump works there is power to the ignition switch, as the fuel pump is on the white wire circuit along with the ignition coil.

For all of the lights (except turn signals and brakes), check for proper hookup of the lighting switch. For everything else not working, check around the green wire fuse.

I am installing the wiring harness in my A also. I check every circuit as I go. I printed out everything Barney has in the electrical section and have it in a 3 ring binder which I refer to as I go. The binder lives in the car. I have also read every page twice. Thanks Barney! The wiring harness is to expensive and time consuming to reinstall to let the smoke out.

A bit of an update..finally have all the lights working, combination of a bad switch and shoddy wiring by me. Now I am trying to figure out the turn signals, it is a 1500. I have tested the dash switch and it is working fine, and I have 12 volts at the relay box on the green and yellow wire, don't recall if this is L or R. Anyway.. I can probably assume that the relay is not working, as so far nothing original to this car has worked as it should. Question.. should the map light only work when the light switch is on? BTW.. I am using Barney's suggestion of the 10 amp battery charger for this trouble shooting..

On the map light question..Barny's site sez.. "This includes a power supply wire for the fog lamp switch, the dash lamp dimmer switch, and the map light switch, so those lamps will go off when the parking lights are switched off." Still battling the turn signals..

Also..hard to believe but the rheostat for the dash lights does not work... I currently have the red and red and while wires on the same connector screw..defeating the switch, seems to be working ok.. anyone have reservations about this? Like the MGB I can't ever imagine wanting to "dim" the dash lights!

I can't see any reason to not gang them together if the dimmer pot isn't working. Mine works, the gauges are almost readable at night. The dimmer is a different construction than the later style on the MGB, a shot of circuit cleaner into it might get it working again.

I think my map light function is the same. It sort of makes sense in a way; wired to the park lights you are less likely to leave it on and drain the battery.

I've long advocated using a small charger to do a new wiring system checkout. Saved me from slagging a new harness in my B.

David,
I agree about the dimmer switch, mine works but I could not ever imagine using anything but its brightest setting.