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MG TD TF 1500 - Turn signal gremlins.

I'm finally ready to hit the road with TD 4834. I have a new Moss early model TD harness w/ embedded turn signals (not the add on harness), a new Moss relay box, a new electronic flasher ( I have LEDs in the tail lights) and a NOS Lucas pneumatic indicator switch in TD 4834

I'm having a problem that I can't seem to find the solution to and hoping someone with more experience and a possible answer. With the key off all lights work except the turn signals. With the key on all lights work but the turn signals flash as emergency lights on all four corners. Doesn't matter is lights are off, markers only or headlidlight. The turns signals flash as 4 ways. Flipping the indicator lever left or right has no effect, all continue to flash. The indicator switch is wired as per the WSM.

Any ideas as where to look? I am at my wits end with this. I am not an electrician and the diagrams are difficult for me to follow


I also have a single black wire that comes out of the harness with the white coil wire. It has a small eye terminal on it but I don't know where it goes. Picture shows the wire on my finger tip.

Thanks.

Bill Chasser
TD 4834

W. A. Chasserq

Bill, you don't mention a hazard switch that should switch the emergency lights on/off. It seems the hazard switch is linked to igniton+ for some reason, which would be wrong. Hazard lighs must work w/o ignitiin on.
When hazard lights are on, the indicator switch has no role, so that bevavior is correct.
Rgds Mike
Mike Fritsch

Mike there is no hazard switch installed.
W. A. Chasserq

The black wires on a TD are earth or ground Bill however I'm not aware of a ground in that vicinity. There is a single black wire that earths the distributor body but I don't think that could be it as it's too far from the dizzy. Could it possibly be an earth for the turn switch? I do know there were problems with the ignition switches that Moss were selling a couple of years ago as they were apparently incorrectly wired internally, some actually causing fires. Is your ignition/light switch new, reconditioned or or an original? Cheers
Peter TD 5801
P Hehir

Hi Peter. The switches are originals that dad and I overhauled prior to his passing. The turn switch is NOS. We sent you pics of the switches as we were working on them before you did yours. I looked at TD24060 and it has the same wire grounded to the firewall at a hole below the coil bracket. TD4834 doesn't have this hole however. I'll extend it to a suitable placement without punching more holes. I will likely be pulling this harness for the td/c and buying another harness for this one as the harness loom tracer wire is the wrong color. Harness came with the car when I bought it.

Cheers Mate

Bill Chasser
TD-4834
W. A. Chasserq

Rhode Island Wiring does great work on harnesses so if you are thinking of a replacement I'd recommend them. I got my battery cables there & their work is first rate. Cheers Bill.
Peter TD 5801
P Hehir

My TD 10835 uses one of the coil mounting bolts for the black ground wire (the one you are pointing to). I recall that I had to change the terminal, as it was a small one like in your picture. If you are worried about the "tracer" in the covering, it would be easy to dye black. Most common turn signal problem: faulty grounds. You have at least one ground (the one in your picture) not connected- that alone could be the fault. The relay box itself must also be grounded. David DuBois (I think) somewhere has a great article on grounds- using a special tool to remove paint around bolt holes, using a copper coat material to prevent corrosion, etc. Bolting the relay box to a freshly painted bulkhead will likely be totally insulated. You have proved the flasher works, so that is not it. If fixing grounds does not work, the start checking terminal/wire color connections. It is very easy to mis-wire at the relay box. See if you can find some of the color coded wiring diagrams that were around a few years ago, vastly easier to read. Two separate circuits: the head/tail/side/ tag lamps are all fed through the brown wire from the hot side of the starter switch to the headlamp/ignition and dimmer switches (unfused!). Turns and brake lights have a different path, being energized through the same feed to the switch but the out controlled through the key, then to the fuse box, and then to the brake/turn signal stuff, etc. BTW, it was the horn/dipper switches that were mis-wired. George
George Butz

George I'm personally aware of two TD owners here in Sydney who purchased the faulty Moss ignition switches & subsequently had to replace them. I wasn't aware that there were also problems with the Moss horn/dipper switches. I'll chase up the Dave DuBois article on effecting a good earth to the painted tub as this has always been of concern to me. Paint is an effective insulator with metal to metal being the ideal conductor, but also the most prone to rust. Cheers
Peter TD 5801
P Hehir

Bill, attached is a generic wiring diagram for the flasher and relay unit that someone from this forum had produced some time ago.
In principle, if all 4 flashers are on with ignition, that means

a) ignition turns on the power to the flasher relay (via the wire with the red 3). This is correct.

b) The relay (on the left side of the picture) in normal state connects the rear lights to the brake light switch (pin 5) and opens the contact to the front flashers.
When either pin 4 or pin 8 get positive voltage, the respective indicators are connected to the flasher output that comes in at pin 1.
All 4 flashers are on when BOTH pin 8 and pin 4 have positive voltage.

That leaves 2 possibilities imho:

1) both pin 8 and pin 4 have positive voltage at the same time constantly --> wrong wiring of the flasher switch or fault in the switch. You can check that with a voltmeter or disconnect both wires at the relay (flashing should stop then) and put + on the contacts with a piece of wire individually.

2) Missing ground connection of the relay causes erratic behaviour. You can check that by connecting the relay ground connector or case to the car chassis with a piece of wire. This is not likely, though, if the behaviour is independent of the flasher switch.

Note when I say "positive or "+" that is based on the car being wired for negative ground.

Rgds, Mike



Mike Fritsch

I had not heard of ignition switch issues, good to get that info out there. The horn/dimmer switches that were pre-wired had the color coded wires placed in the wrong position. I think there was also a recent batch of foot operated dimmer switches that were bad. Definitely bad quality control, or maybe the prince of darkness is still lurking.... Bill, read this article: http://mgaguru.com/mgtech/electric/et105.htm , mostly applicable. George
George Butz

Before you chase any more Bill, put some standard filament bulbs in and see if you still have the problem. I put some LED's in the MGB about a year and a half ago. When I put the supercharger in 6 months later I changed out some gauges ...specifically a boost gauge and a combo oil/temp gauge. When lit, the combo gauge shows just a little light from the center needles that you can see in the day time...something none of the other gauges did or still do. Not long after I installed the blower I noticed that when I stepped on the brake that the dash lights would come on. Huh? I spent several days rechecking my wiring under the dash, under the hood (I installed an A/F gauge as well) and still the issue persisted. When I finally got the the back of the car I removed the LED bulbs and stepped on the brake..... the dash lights did not illuminate. I put the old bulbs back in and no more problem. It didn't make any sense to me as the LED's were back feeding voltage through the parking light circuit...it just din't make sense, but never the less that is what was happening. They were crappy LED's from a local parts store I had bought for the TF but wouldn't work at all with positive ground..not surprising but the counter said they would and there wasn't any mention of polarity on the package. I gave them away to somebody else. Just something that would be easy to check.
L E D LaVerne

Thanks Laverne. I will try your suggestion as well and report back next week. I installed the LEDs because they were much brighter. I switched to negative ground and I did buy the tail bulbs from the local auto store. I also installed LEDs in the dash gauges as well. Those came from Moss. I hope that is not the problem as I wanted the added safety factor and minimal current draw

Cheers

Bill Chasser
TD-4834
W. A. Chasserq

With negative ground, normal LEDs should work fine. Most are bipolar these days, only cheap ones are not (but will work with negative ground anyway).
I have those dual color swithcback LEDs in the front pilots that have yellow and white in one bulb. They work great, much brighter than the dual bulb versions and no relay required (the bulbs do that themselves).

Rgds, Mike
Mike Fritsch

See attachment showing how to either fix a broken relay box or build one from scratch. The two double throw double contact relays are available from Maplin at £3 each and are sealed for life. They will easily fit under the cover of the original Lucas relay box and are rated at 8A.
1) When the stop lamp switch is activated current flows to the rear lamps but is stopped from the front ones by the second sets of relay contacts.
2) Flick the indicator switch and both sets of relay points change over in the appropriate relay.
3) Current now flows from the flasher unit to front and rear lamps at the appropriate side.
4) If the brakes are, or were, applied only the opposite side rear lamp lights.

If anyone wants to know which relay terminal is wired to the terminals on the original Lucas box I do have a schematic diagram. I also have diagrams using conventional automotive relays but you will need four of them and try cost about £5 each

J Targosz

I forgot to add that the relay coils are independent of the flasher circuitry and an electronic flasher unit and compatible LED bulbs will work perfectly.

Jan T
J Targosz

You've almost certainly got something miswired, probably at the relay box. Be sure you have the right wires to the right terminals, and especially make sure you've interpreted the terminal numbering correctly. Beyond that, make sure the wires are hooked up right at the lights and the grounds are good--don't connect them to painted surfaces, or they might not make contact.
S Maas

LaVerne and others,

I design and manufacture LED tail lights, so I think I know of which I speak. So, many of the less expensive LEDs (mine are good, but not expensive), do not have polarity protection. This is usually just a diode which prevents two things: 1) it protects the circuitry from inadvertent reversed polarity. 2) It prevents current feedback when the LEDs are not on.
It could well be that such diodes are not placed in the lesser expensive LEDs for economic reasons. Many of these are manufactured in China and they probably don't drive too many pre-1956 MGs.

Before anyone asks, my product line is currently limited to pre-1950 MGs and a few others. I will likely be adding TD/TF, MGA (especially the 1600 MK II) and pre-1970 MGBs sometime in the not too distant future.

But if you have a need for the ST38, ST51, or 288 tail lamps, contact me at lew (at) roundaboutmanor (dot) com

Lew Palmer
Lew3

Bill,
The other thing that occurs to me is that with a positive ground car, for example, the positive voltage is fed to the shell of the base and negative voltage to the tip. (Negative ground cars are just the reverse).
If you have any other incandescent bulbs on the same circuit (e.g. license plate light, turn signals at the front, turn signal warning lamp, etc.) which are connected in reverse (with a positive ground car negative voltage to the shell and positive to the tip), this is very likely to cause all manner of gremlins.
A bad ground connection anywhere in the circuit can also cause LEDs to not operate. The incandescent bulb will draw more current than an LED, and since an LED bulb and draw around 80% less current, the resistance due to the bad ground may limit the power available to the LED.

Lew Palmer
Lew3

Hi Lew and others. The LEDS are only in the tail lights and dash gauges. I could nt find any for the front wings or plate. They are functioning and all flash simultainiously with equal brilliance so I don't think it is a ground issue. They simply all flash when the key is on and with the indicator switch in any position i.e. Left, neutral or right.
I haven't had a chance to look further into the problem this last week as I have been at a dog agility competition. Hope to get the car back out of the trailer tomorrow and investigate it further. The switch is wired correctly so it must either be the flasher or the relay box. Neither of which are easy to get to especially with my physical disabilities I will report my findings. Thank you all for the correct trains of thought

Bill Chasser
TD-4834
W. A. Chasserq

Thanks Lew...yes these were some cheap Chinese crap. I found it strange that they would back feed voltage since a diode is a one way directional for the electron flow. One of the days I'll put something brighter in the TF. It just makes sense.
L E D LaVerne

Bill, I think you missed my point. I realize you only have the LEDs in the tail and dash. However, with the LEDs wired in, the polarity is obviously correct on THOSE. But if other lamps are incandescent, you MUST be sure the base of those are also wired to the ground circuit. It is easy to reverse the polarity to the incandescent bulbs, as they are not polarity sensitive. But having the incandescent bulbs wired in reverse, they can play havoc with the LEDs.

Lew Palmer
Lew3

Any news on this one yet?
Rgds, Mike
Mike Fritsch

No progress yet. I have been unable to get to it because of the heat
Will keep you posted

Bill Chasser
TD-4834
W. A. Chasser

"They are functioning and all flash simultaneously with equal brilliance so I don't think it is a ground issue." Bill, I spent hours in my youth tracking down weird boat trailer signal problems and it always ended up being a ground problem. The ungrounded eyelet in your harness and the relay box positively have to be grounded. May or may not be the problem, but needs to be done anyway.
George Butz

Bill
I don't know if it has any relevance.
But I remember reading somewhere that the cover on the relay box can be put on backwards? Which makes all the indicated terminal numbers on the lid incorrect. There is an indication I believe to show which way round it should go on.
It has been too long since I mounted mine to be sure.
Just a thought.
Rod

R D Jones - Ex Pat

See http://www.ttalk.info/Directionals.htm for a note on the orientation. Bud
Bud Krueger

Well I looked into it a bit last week. The indicator switch is wired correctly. The relay box was new from Moss and the cover hadn't been removed that I'm aware of unless it was installed incorrectly during manufacture. The wires are in their correct positions. The flasher relay I haven't gotten to yet as I'll have to remove it from its mounting point to review it. I do note that the left fry wing is dimmer than the right and this seems to have a bad ground. I have a ground wire coming out of the main harness with the hot wart for the ignition coil. I need to change the eye terminal to mount it to the coil mounting bolt to the cowl. So that is next on the list. To try when I get back home.

I'll report back mid week

Bill Chasser

TD-4834
W. A. Chasser

Don't know if this true but it's interesting.
Mike
http://www.ebay.com/gds/LED-Turn-Signal-Bulbs-Flashing-Problems-/10000000176783681/g.html
Mike Hart

Okay. I got under the dash and disconnected the wires from the indicator switch. Relay is still flashing and I have four way indicators without the benefit of a hazard light switch. I have the lt front wing marker that has a a poor ground based on its dimness. I will try to get to the bottom of that first.

Bill Chasser
TD-4834
W. A. Chasser

This thread was discussed between 15/06/2016 and 06/07/2016

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