The MGA With An Attitude
Intermittent Wipers Tech -- ET-210 - Pg 5 of 9

Here are pictures of the only wiring change I made in the engine bay. The green wire supplying power directly from the switched fuse to the wiper motor has to be disconnected, and the new control unit will be wired in series with this circuit. Rather than running two (or more) of the wires from the control unit through the bulkhead and connecting them at the fuse block, I chose to run the wiper power wire through the bulkhead and make all of the new electrical connections hidden under the dash.
MGA intermittent wiper control unit
The first order of business here is to determine which of the four green wires connects to the wiper motor. You can do this in just two steps. Disconnect any two green wires from the fuse block. Switch on ignition and wipers and see if they run. If it doesn't run, one of these wires is the wiper motor supply. If it does run, you have two of the wrong wires, and you can reconnect them and work on the other two wires. When you have it narrowed down to only two wires, disconnect one and leave the other one connected. If it does not run, you have disconnected the right wire. If it does run, just reconnect the loose wire and disconnect the only one left.
MGA intermittent wiper control unit
Then the green wiper supply wire has to be connected to one of the blue wires on the new control unit. I chose to make all of the connections inside the car, so I had to pass the green wire through the bulkhead cable grommet. This pass-through grommet is located on the bulkhead well down behind the heater box where it's rather tough access for human hands. To make the job easy I used a stiff wire (in this case a gas welding rod) with a small hook formed on the end, shoved it through the grommet next to the harness cable from inside the car, ran the green wire into the hook, and then pulled the wire back through the grommet. Quick and simple, and no damage to the rubber grommet. This green wiper supply wire is easily long enough to pass a few inches through through the firewall.
MGA intermittent wiper control unit
And here is the final result. This is the only visible wiring change in the engine compartment, and this is back low behind the heater box (except for the one green wire being missing from the fuse block).

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