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MG TD TF 1500 - Nitty details--TF wiring harness routing

I'm finally attaching the wiring harness (loom) to the dash, and I think I've figured out which wire is connected to which. Actually, I've had to fabricate a few jumpers and a new harness for the map lights and the instrument illumination lights, and I will probably make a grounding harness.

The wiring I pulled out was a rat's nest, and the harness looked to be a combination of homemade parts and salvaged stuff with some real bodges, like a cheap toggle switch for the windshield wipers. The PO had also replaced the little indicators with larger generic lights, and drilled nasty big holes in the dash to install them. I welded plugs into the holes, and cut holes of the correct size. It actually looks pretty good.

Unfortunately, the new wiring also looks pretty messy right now. I'd like to neaten it up by trimming the lengths of the wires, but I need to be pretty sure of how to route the harness before I do that. I have pretty good records of how the wiring is routed on the frame, but I'm not sure of how it is routed inside the tub. BTW, the car is right-hand drive, but I don't think this makes much difference, since all of the instruments are central on the dash. There is a 'branch' that goes to the turn signals/horn switch, but that looks like that can be easily be flipped from left to right.

OK, after that VERY long-winded introduction, does anyone know how to route the wiring under the scuttle? Where it is clamped? Does the pigtail to the turn signal switch go over or under the glovebox?

One thing I haven't figured out is how the wiper switch is wired in. The wiring diagram in the workshop manual shows the motor hooked to the green (hot when ignition is on) wire, but seems to omit the switch. I assume the switch goes in the circuit between the fuse and the motor. I can probably figure it out with a multimeter. I have repaired the switch and it works correctly ...
Mark Barrington

Mark,

Had the same problem and took digital photos of the underside of the dashes of about a dozen TDs at the recent MG Silverstone event. Will look them out and e-m to you.


Jan T
Jan Targosz

Thanks Jan. Somehow, I forgot to mention that the car is a '55 TF 1500. I expect the TD wiring will be routed similarly. Except for that 'two gloveboxes' thing. I look forward to seeing the pictures.

There are also some good pictures at 'The Original mgtf midget' site ( http://www.mgcars.org.uk/mgtf/ ), in the unrestored examples area http://www.mgcars.org.uk/mgtf/Pictures/Unrestored/Thumbnails/mgtf_gallery_unrestored.htm . This site, which is maintained by Chris Couper and a few others, is very useful. I see they've been working hard on it, and the content keeps improving.

The original examples depicted on TOMGTFM site seem to indicate that the original wiring behind the dash came from the factory pretty much as a rat's nest, so maybe I shouldn't worry too much about making it neat under there, but I hope to at least make it a little better-organized, by ganging wires with cable ties and routing wires in bunches as needed.

MB

Mark B.

in the TF:
1) the wiper switch is in the ground side of the circuit. The motor is always "HOT". The ignition switched hot wire (green) comes to the motor. then a wire goes to the switch. The wire from the other side of the switch comes back and is fasened via an eylet to the lower cover screw on the motor (assuming the frame of the motor to be grounded. the two wires to and from the switch are paired in a black cloth cover. They are now both black on my car.
The pigtail to the turn switch goes over the appropriate glove box.

My car has been rewired so I can't tell the original routing of the main harness as mine all goes thru a fuse box with all individual circuits fused.
Don Harmer

So if I understand you correctly, Don, I will have to fabricate a little two wire pigtail from the motor to the switch. I'll try to figure it out tonight. I don't understand where the return from the motor to the sw is hooked, and why the return from the sw has to go all the way back to the motor. This design seems excessively complicated. But it is an MG after all.

There are four green bullet connectors that come out of the harness somewhere near where the switch is located. From the wiring diagram, it looks like these get all ganged up with a 4-way connector, instead of one of them going to the wiper switch, like I was thinking.

Anyway, I broke one of the little plastic things the lights shine through last night (the blue one). I think these are called 'gems'. I have a spare, since I got two complete sets with the two sockets I bought from Moss. By the time the grounding connector and the bakelite insulator is in place, the socket only has a few threads to grab onto the gem. Probably the repair I did to the dash also made it effectively thicker, too.

Unfortunately, finding a tiny part like the extra blue gem is frustrating, to say the least. I think I will devote a few hours to organizing my workspace. Not that any of this is of interest to those of you reading the board. I just had to vent a bit.

BTW, I wanted to thank the BBS readers that sent me pictures and advice. It's been very helpful.
Mark B.

Mark,

First of all we have to get over the bad practice of putting the switch on the ground side of the motor!

A small brown wire (about 18 gauge) runs from the motor to the switch, Then a BLACK wire runs back to the gear box cover. If you look at the cover there are 3 hex screws. On above the other in the rearward facing "pointy end" and one at the "front" ( next to the actual motor). The BLACK wire is fastened (via a small eylet) under the lower ( towards the side panel) of the two screws at the rear.

Why not the nearest ground? Only the MOWOG knows!

There is no way you could have figured out this wiring, even if it had been ingluded in the schematic>
Don Harmer

I think I've almost got it, Don. The only thing I don't know is where the pigtail to the switch comes through the bulkhead. I guess it would be least obtrusive to sneak it through the same hole the rest of the wiring exits on that side. Is that correct?

P.S. Thanks for the explanation. The design makes no sense at all, but I've been staring at the problem long enough that your description actually makes sense. I may put a fuse somewhere into this circuit, even though it is already fused with the main green circuit fuse.
Mark B.

Yes, the twin wires come thru the same hole as the other wiring on the right side of the bulkhead.
Don Harmer

<<<snip>>>
First of all we have to get over the bad practice of putting the switch on the ground side of the motor!
<<<snip>>>
It has to be done that way in order to have the wipers self park. If the switch is used to POWER the motor, then the motor would need TWO hot leads.
Bullwinkle

Interesting theory, Bullwinkle, and it has the ring of truth. But to make this work, there has to be another switch that 'senses' the position of the rack (probably in the gearbox, but maybe in a wheelhouse) and keeps the connection closed (by bridging to ground) until the wipers go into the 'parked' position.

The only problem with this on my car is that I've dissassembled the motor and wheelhouses and I haven't encountered the second ('parking') switch. Either I've got the wrong motor, the PO has somehow removed the parking sw, or I dont fully understand how this works. Now I've got to put the whole thing together on a test bench and try to make it work.
Mark B.

The "park" on the TF wiper is manual! You push the knob in, disenguage the clutch (and shut off the motor) and then move the knob to whatever position you want to park the blades and let it back out.
Don Harmer

Mark,

Do you know that the ignition and turn signal warning lights ground to the dash, but the fuel warning light doesn't? The fuel warning light is the only one that should have the insulator (I think the fuel sender completes the ground when the fuel level drops).

At least the other two will thread onto the lens a little easier. I know it is a frustrating experience, being very easy to cross-thread the lenses, and then to have them disappear when you drop them!

Greg
TF 6846 XPEG 797 NEMGTR #12312
TC 6669 XPAG 7170 NEMGTR #3777
Greg Van Hook

Mark:

I thought the TF wiper motor was the same as the MGA motor. Apparently it is not.
Bullwinkle

Greg, I think the fuel light doesn't ground to the frame because the cork gasket which seals the sender to the tank isolates it. Therefore it grounds to the sender casing, which is then to be directly connected to the light. They could have put in a ground wire from the sender to the frame, but didn't, perhaps for safety reasons? AB
Adrian Bennett

Greg,
The ignition warning light does not connect to ground. It connects between the battery circuit and the generator output. That's the same way for a TD or a TF. The fuel level lamp in a TD closes the bulb circuit to gound at the fuel tank when the switch contacts close. The shop manual wiring diagram for the TF (N.29) shows that a separate wire goes from the switch to ground.
Bud Krueger

Thanks for the info guys. I have both the ignition wiring light and the fuel light insulated from the dash with the bakelite insulators. I believe this is correct, as it is that way on the TF wiring diagram in the workshop manual.

It makes sense that current flows through the fuel warning bulb before it flows through the tank sensor for safety reasons. If the fuel warning circuit is shorted out, the bulb acts as a current limiter. A full current short through the fuel tank sensor could be dangerous. I won't get into why the ignition light isn't grounded, because Bud covered it.

I may drill and tap a hole in the side of the light sockets to attach the grounding lugs for these two lights, as this will cut down on the effective thickness of the 'stack' threaded onto the plastic lens in the dash. With everything attached, the socket only grabs about one thread on the plastic lens (the 'gem?') and will snap off the plastic threads when you pull out the bulb holder, unless you are VERY gentle.
Mark B.

Oops, sorry for the mis-information. I do recall on the TC, which I just rewired this past spring and actually still have brain cell recognition, the ignition light was definitely NOT grounded on the instrument panel. Again, I apologize.

Greg
Greg Van Hook

This thread was discussed between 13/08/2003 and 21/08/2003

MG TD TF 1500 index

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