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MG MGA - HELP! New Electrical Install Problems

I have a brand new harness for a '58 Coupe. The initial installation seemed to go perfectly. I have also upgraded to an altenator instead of a generator and have made the necessary wiring changes to the volt regulator (per the altenator instructions). I have also grounded the dash guages according to the eletrical plan provided in my manual. I am testing my connections using a 14 volt battery from a hilti cordless drill alligator clipped to the battery cables. So far the following components work:
Lamp Switch
Head Lamps
Parking Lamps
Tail Lamps
Brights/Dimmer switch
Ignition Switch
Ignition Indicator Light
Gas Pump
Ignition Coil

The following components do not appear to be receiving power:
Turn Signal
Heater Motor
Dash Lights

If I attach the power source directly to the heater motor wire under the dash I can make the motor work. However I do not get power to that wire otherwise. Also according to the manual there is a green wire that should be connected to the 'B' terminal of the fuel guage and run to the Turn Signal Switch and the Heater Motor Switch.

I'm afraid to use a car battery to test these connections.

Can anyone help me trouble shoot my problem?
gerard hutchinson

Sounds like you have two different problems, one of which could be a bad fuse or a bad connection at the fuse block. The fused items are the turn signals, the heater motor, the wipers, the brake lights, and the fuel gauge. The other fuse is only for the horn.

The panel light problem is most likely the red wire to the light switch. There are a lot of red wires going to that one terminal and it is hard to get them all in there.

Jeff Schultz

A circuit breaker temporarily installed between the brown wire and the starter switch allows you to test all the circuits with no fear of letting the smoke out of the wires. Once all works properly it can be hooked up properly.
R J Brown

Start here: http://mgaguru.com/mgtech/electric/circ_f2.htm
The fuel gauge gets power via a green wire from the fuse block. The same terminal on the fuel gauge then supplies power to the heater switch and turn signal switch (on the 1500). If no power to the fuel gauge, check the green wires at the fuse block.

For your dash light problem, start here: http://mgaguru.com/mgtech/electric/circ_d.htm
Read carefully the last paragraph on the page. Notice four red wires on lighting switch S1 terminal. One of those runs to the fog lamp switch. These FIVE red wire ends emerge from the harness at the same place, but two of them are opposite ends of the same wire. One of those ends must connect to the fog lamp switch. If you get this wrong TWO devices will not work (like no dash lights and no fog light power).

This can be a real head scratcher until you figure out which two wire ends are the common wire. When in doubt you can disconnect all five red wires and use an ohm meter or continuity tester to find the two ends of the same wire.

I have no idea how the factory workers handled this issue on the production line. If I was in that seat "back in the day", I probably would have filed a request to the drawing department to relocate one of the common wire ends to emerge from a slightly different location on the harness.
Barney Gaylord

This thread was discussed between 01/03/2008 and 02/03/2008

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