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MG TD TF 1500 - Moss turn signal relay box

Hi Gang;
What is the collective experience with the Moss turn signal relay box? I have gone through my second one in the last few years, the second one being the new improved one. The right turn side always works for both of the boxes. My failures seems to be associated with the left turn side. When the switch is engaged the box clicks, the flasher clicks and an audio beeper I have connected beeps, however, the left side lights do not flash. Disconnecting leads 2 and 3 from the box and powering them separately with 12 volts results in both lights operating properly, eliminating the usual questions about wiring or grounds.

Removing the cover of the second relay box is fruitless because, unlike the older box, the protective covers over the two relays are not removable. This prevents any attempt to adjust the points as I used to do with the older box. As these things are substantially over priced I do not want to purchase another potential problem without getting smarter about the problems. On the other hand I do not relish driving on US 1 in south Florida during tourist season without it, especially when we use a gas tank as a rear bumper.

Thanks

Dick McCutcheon (20102/20455)
Stuart, Fl

Safety Fast
Richard McCutcheon

Dick, one of the forum's Daves (DuBois?) has a set of plans for a DIY directionls relay system that is great. I'll try find it for you. Hopefully, the Dave will jump in. Bud
Bud Krueger

Dick, try
http://www.mg-tabc.org/techn-up/turn_signal_relay/turnsignalrelay.html Bud
Bud Krueger

Dick, I make a relay box, but don't have a set of instructions on the process. The link that Bud provided does have a set of instructions. The new Moss relay box is basically the same as the one in the link - just with a circuit card for the relay mounting and connections. You should be able to use a meter to check each lead coming out of the box for the proper voltage/connections through the internal relays. Following the diagram in the link that Bud supplied should show what to expect at each point. Cheers - Dave
David DuBois

it is possible to have two bad boxes...each exhibiting the exact same failure mode...OR...one bad car circuit. just sayin'. regards, tom
tom peterson

Hi Gang

It seems to me that the diagrams noted are for single element bulbs and I am running dual element bulbs, front and rear. I made the change over when I restored the car 15 years ago and the turn signal system was installed then when I put in a new wiring harness.

It worked for several years with the original box and then I started to have problems from time to time which I repaired(?) by adjusting and cleaning the relay points. Two years ago I broke down and purchased a new improved box which lasted until about three weeks ago. When I pulled the box cover I found that the relays points were not accessible for adjustment. Before I jump off the cliff into the overpriced waters again I just thought I would survey the population regarding the subject.

Thanks

Dick (20102/20455)
Stuart, Fl

Safety Fast
Richard McCutcheon

Boy, I must have lucked out. When I restored my TD, 12 Years ago I must have gotten one of the last real relay types from Moss. Paid a rediculus price, but it works OK.

My guess is that the left side of your car somehow has an inductor on the output side that is causing the arcing at the contacts in the relay. That is in turn causing the left side to fail. The problem could be that some wires in the harness are not quite the correct color and have caused the the relay coil to be connected to the output of the left side.

Look at the relays, they are probably marked on the top with the relay makers name and model number. Then go to Digikey or other electronics supplier and get a replacement relay. Local Radio Amateurs will have the expertise to un-solder the original relay and solder in the new one.

It will take a good bit of detective work to find the problem of why the relays fail. Good luck finding it.
Cheers,
Bob
Bob Jeffers

Mate

I dont know how accessible the construction of this device is as I am not familiar with the product. If you can locate the wiring to the relay coils I suggest the following;

Ascertain if their is a diode wired across the connections to the relay coils, if there is not solder some low current diodes across these connections so they are in reverse polarity to the coils energisation voltage. This process completely removes the induced voltages created by the coils inductance interfering with other circuit functions.

If these diodes are not installed circuits of this type often malfunction because of this phenomena.

If you are struggling with what I am communicating contact me and I can provide additional advice.
G Evans

Go to http://mgaguru.com/mgtech/electric/ts202.htm. It might work for you. Marvin
Marvin Stuart

FYI, a bit more: http://www.ttalk.info/Directionals.htm Bud
Bud Krueger

Dick - I really don't believe that the relays are the problem. The relays in the original box would handle enough current to use the headlights for turn signals and the newer relays will handle almost as much current. Both relay boxes work with double filament bulbs, so that is not the problem. I suspect that both boxes may have some connection problems rather than the relays themselves. One test you can do it to step on the brakes and, keeping you foot on the brake turn the signal switch to the right, the brake light on that side should start blinking. Now do the same thing for the left side and see if the brake light goes out on that side - if it doesn't, then the relay is not being activated by the turn signal switch. I don't know where Moss has their relay boxes manufactured, but it it is off shore, you could well have some bad solder joints for the individual relays. If you will send me the relay box that isn't being used, I will put it on a test stand and check it out. If it is in fact bad, I will see if I can repair it such that it will stay repaired and send it back to you. You can then send me the other box and I'll do the same for it. E-mail me at SUfuelpumps@donobi.net and I'll send you my postal address. Cheers - Dave
David DuBois

Hi gang;

The turn signals work on both sides this morning, although I don't know why. To clarify the situation, the brake light circuit bypasses the turn signal relay box completely and is powered separately. The separate 12v powers a Ron Francis brake pressure switch which in turn powers a separate single relay for the standard and third brake light dual element bulbs. This configuration leaves the turn signal relay box allocated to the turn signals only.

I was fooling around this morning and decided to disconnect the wire from the flasher to the relay box and replace it with 12v from the battery. This allows circuit checks without the annoying flasher interruptions. When I selected right turn (the working side) I got steady right side lights until the selector switch shut off. When I selected the left side there was nothing, indicating to me that the left side relay was bad. I reattached the flasher connection and checked operation with no change. At that point I realized that there was still a wire attached to contact five on the box even though there has not been any brake light function there for years. I checked the wire for voltage and there was none, ignition switch on or off. I tied the wire back and checked the turn signal operation again. The turn signals now operate properly for both sides. I think I will get a beer and go sit in the corner! Don't you just love electronics?

Thanks for your inputs
Dick
Stuart, Fl

Safety Fast
Richard McCutcheon

"Don't you just love electronics" yup sure do, made a pretty good living working with them since 1949.
Cheers,
Bob
Bob Jeffers

This thread was discussed between 18/11/2011 and 19/11/2011

MG TD TF 1500 index

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