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MG MGB Technical - yet another stupid question

OK, here's a good one. One engine came out...another engine went in, now brake lights don't work. I found a wiring harness with 2 wires coming into it that match the colours of those that are supposed to be for the brake light switch. The harness is over by the brake MC, and on the back of the MC there are 2 wires of the same colour going into it. Both of these wires and the ones from the mystery harness disappear into the taped-up wiring system. I have hypothesized that this "mystery harness" is responsible for my brake lights not working (yes i tested the bulbs and they work, and no I didn't break out the multimeter because it spontaniously decided not to work, and I lost the little electrode dealies for it). I have searched throughout the engine bay and cannot find a place for it to plug into, and I don't rmember anything going through the firewall, and I certainly don't remember pulling anything back out through the firewall.

My question has two parts:
1) Am I likely well based in making this hypothesis?

2) Where does this "mystery harness" go?
Dave

Replacing the engine shouldn't have altered the brake-light wiring at all, so even if you disconnected it to swap the engine it should just be a matter of replacing everything as you found it. You do mean the brake lights and not the reverse lights (which *will* be affected by an engine swap if the gearbox came out too), I presume?

The master cylinder may have brake failure test and warning circuit wiring (both wires are black/white) but not brake-light wiring, which has green on one side of the switch and green/purple on the other.

The brake-light switch should either be on the pedal box (later cars) or brake hydraulic line on earlier cars. With the ignition on short-out the brake-light switch. If the lights come on the switch is faulty. If they don't, with them still shorted, check for 12v on the two wires. If you see it there is a broken or bad connection in the green/purple to the lights. If not there is a broken or bad connection in the green to the fuse-box.
Paul Hunt

Paul,

The new harness I found has a green wire and a green with purple. I just can't figure out if it is supposed to be hooked up, o if it's an old inactive bit that was replaced but not entirely removed. I'll check for more wires coming out of the pedal box and see if a connection is missing its partner. I know swapping the engine shouldn't have done anything, but I thought I should consider it as a possibility, as one of the guys who helped was a bit too eager(he's not allowed within 25 feet of the B now) and may not have known what was and wasn't necessary to disconnect, but claimed to. I do mean the stop lights, I left the gearbox where it was throughout the swap. Good thing too, as the crane I used was too big to fit its legs under the front Xmember and we had it tipped up on end just pulling the engine.

Thanks for the reply, I'll see what I can find now.
Dave

Green and green/purple certainly is brake lights. If it is just a two-wire harness with bullets on one end then it sounds like it should come from the switch and plug into the mass of 2- and 4-way connectors that are by the RHS inner-wing/firewall. Have you found the switch? Does it have those colour wires on it? Are they connected to anything?
Paul Hunt

This thread was discussed between 13/01/2002 and 14/01/2002

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