MG Sports Cars

Hello friends. I am ready to start my '78 B this weekend for the first time. LONG. TIME. COMING. I have three questions about wiring and megasquirt.

I am testing the wiring in my car, which I purchased from Advance Auto Wire. So far I am pleased with the product, and almost everything works. Two of my questions:

1) When I engage either turn signal, all of the hazard lights function. I assume this is because of the DPDT switch supplied, and am going to seperate the circuits by wiring a DPST for the hazards into the existing turn signal circuit (similar to [www.how-to-build-hotrods.com] but utilizing the stock column turn signal switch). I want to know if this would be a problem.

2) My windshield wiper motor runs continuously, until I put the column wiper switch into the second speed. Then the fuse blows out. It runs even with the switch unplugged, and I have rebuilt the switch to no avail. I am going to replace my wiper switch since it only has 5 wires coming out of it... no black wire anywhere to be found. Just wanted to double check and see if anybody has experienced similar issues

Finally, I have a megasquirt question. I used an RS Autosport wiring harness which is nice. I am drawing my fused 2amp power for the MS, as well as the 10amp injector power, from the ignition warning light circuit. I wanted to see if this is a reliable enough source of power to run my MS unit.

Thank you, and sorry for writing a novel. I am so eager to get this thing rolling, but want to ensure I don't make any mistakes. As always, your input is appreciated.

Re: #2 - I doubt your column switch is the problem. It's pretty easy to get windshield wiper wires crossed because IMHO the "auto park" feature isn't especially intuitive.

Luckily, I have Rick Astley's book within arms reach. From his write-up... There should be just four leads connecting the column mounted switch to the wiper motor, and the MG color scheme for them is as follows.

Blue-with-Light Green connects from switch terminal #1 to wiper motor terminal #3.
Green or Green-with-Pink connects from switch terminal #2 (via a 3-way splice clip) to wiper motor terminal #4.
Red-with-Light Green connects from switch terminal #4 to wiper motor terminal #5.
Brown-with-Light Green connects from switch terminal #5 to wiper motor terminal #2.
(Note: the only solid-black wire in the wiper circuit is one that connects the motor housing to chassis ground.)

If you want to test the switch with a continuity tester (i.e. Ohm meter):
(a) in "off" position, terminals #4 and #5 should make a connection
(b) in "normal speed" position, terminals #2 and #4 should make a connection
(c) in "high speed" position, terminals #1 and #2 should make a connection

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I don't think I'm fully comprehending your question about MS wiring. I would probably avoid putting either ECM or injectors in series with a lightbulb filament of any type, and also as you probably know the ECM should be completely isolated from the injectors (via a relay) for electrical noise reasons. Does that help?

The IGN warning light should properly be connected to your alternator's voltage regulator so really it is a dedicated circuit. However if you come off the ignition switch prior to the bulb it is workable to switch on the main power relay for the MegaSquirt. Power to the relay should come from a separate fused unswitched circuit in accordance with MS wiring instructions. Hope that helps.

Jim

1) I would definitely NOT use the wiring shown on the how-to-build-hot-rods site - that is the WRONG way to do it. Check your hazard wiring carefully, comparing it to the diagrams in the instruction manual. This design and been tested and shown to work in hundreds of installations. In particular, check your wiring against the pictorial on page 9.

2) The windshield wiper harness supplied with the kit has 5 wires coming out of it:

The black wire goes to ground. There is no corresponding black wire from the wiper switch.
The green wire goes to the green wire from the switch AND a green power wire from the power block.
The other three wires go to their corresponding color wire on the switch.

If you know your wiper motor is good, recheck your wiring against the diagram.

Curtis: Appreciate the breakdown of the wiper switch leads. I went to the trouble of disassembling the switch to understand the contact sequences. Looks like I will need to quadruple check my work. Any reminder about proper MS wiring is definitely helpful!

Jim: Thanks for the heads up. I am indeed looking to tap the power from between the ignition switch and the ignition warning bulb (shown as a W - 14 line in the Advance Auto Wire schematic). It is good to know that will work for my MS relay. I am looking forward to getting into the wonderful details of tuner studio.

Dan: I am slightly confused by the Advance Auto Wire schematic for the MGB V8 (http://www.advanceautowire.com/latebv8.pdf). As I am reading, it shows the Green power feed G - 14 terminating on the wiper switch at both the Green/Pink-Green AND the Black wires with a small bridge in between. I do not know if this would effect the operation of the motor in any way, or if I am just plain misreading your nice diagram. I will definitely heed your warning on the hazard set up and stick with the system. More troubleshooting!

Gentlemen, your prompt advice is so very helpful. I know you do this out of an earnest love for this hobby, and I do appreciate the guidance. I am going out to the garage and will report back on any progress. I must say, I did drink a victory brew after powering on this new set up. Glad to know the little wiring gremlins can be overcome.



Edited 1 time(s). Last edit at 08/20/2014 11:02PM by Johnous.