MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Turn signal failure

I recently installed an underdash shield in my '53 TD prior to attending a car show. In the process, I had to relocate the turn signal relay to another location under the dash. Got home from the show and removed the shield, which I don't plan to use except for major points events, and realized that I didn't have any turn signals. I discovered that I didn't have a good ground for the relay unit. I made a ground connection but now I only have the left signals, front and back, working. They are flashing at about twice the normal rate as well.
I had a lot of problems getting he flashers to work from the beginning, after doing the body off rebuild, and have a new Moss box and relay which have worked well after getting things sorted out with the help of this forum. Things have been just fine for the last 600 miles.
Nothing has been changed or altered to the wiring recently. I just simply added the underdash shield, loaded the car in the trailer, traveled to the show and discovered that the signals didn't work.

I believe that the key to the mystery could be that the left lights are flashing at twice the normal rate, but I don't know where to go from here.
I checked to make sure that there are no apparent shorts between wires on the box or elsewhere including the indicator switch. I have examined any areas that may have been disturbed by the multiple trial installation and removals of the shield while fitting it to the car and can spot no obvious problems.
There is the normal click in the flasher can when the indicator switch is flipped to the left and nothing in the flasher can when the indicator is flipped to the right side directon. The indicator light on the dash comes on only in the left position. There is also the normal click in the relay itself when the switch is turned in EITHER direction! From that, I can assume that the switch is passing power to the relay unit properly and is most likely okay. It sounds like there is no signal getting to the flasher can from the relay unit to start the flashing process. There just isn't any power apparently being applied to the lights from the flasher. Since the flasher works in one direction, I suppose it would be okay in the other direction since it is the same internal circuit. I can't imagine that the relay unit went south on me by just moving it to another location 2 inches from where it was. There has to be an open ciruit somewhere, but where? And how could that be or where might it be?
Any ideas floating around out there as to what I can do next? I've been unable to find anything in the archives that has helped me on this one.

Mark
Mark Strang

Mark, see http://www.ttalk.info/The53.htm for location of the Direction Indicator Relay Unit from 'the53' that I'm working on. If you can hear the relay actuating when you select either left or right you know that the wiring to, and from, the turn signal switch is okay and that the relay is grounded. If the indicator light works at all, you know that the wiring at the flasher is okay. What's left is the wiring from the relay unit to the lamps. The flasher operates by means of the current going through it to the lamps. Do you have access to the terminals of the relay that would allow you to remove/swap wires? Bud
Bud Krueger (TD10855)

Bud,
I can get to the relay for access to the terminals so I guess that I can swap wires. Are you suggesting that I try to hook the right side wires to the left side terminals to see if the light wiring is okay?

Mark
Mark Strang

Mark,

Sometimes the fittings of the wires going to the relay are not well crimped. Check the continuity of every wire on the relay are good. Check the grounds at every light in the circuit, scrape and apply dielectric grease as needed. Make sure the front lamps are right side up in their sockets as they are straight pin lamps. An upside down lamp on a sensitive flasher could cause it to flash faster as the parking element current requirement is less than the bright flashing element's.

Hope this helps,
dave
Dave Braun

Hi Mark,
The fast flashing could indicate a bad ground at one of the lamp units, or a bad bulb. I think the TD & TF ground arrangement for the lamp assy at the front at least is the same, and relies upon good mounting bolt connections at the lamp assy & the fender to the chassis. I ran separate ground wires in the harness from the front lamps to the chassis in our TF. That doesn't explain the non-flashing side.
A W Parker

I agree with the above....Sounds like a ground problem at one of the lamp housings....
I had a similar problem with one headlight, and ended up having to run a separate ground wire to the frame...Could not get a decent ground connection any other way.
Let us know what you find.
Edward
E.B. Wesson

There are a couple of things that you can readily do, Mark. Referencing the wiring diagram on page N.23 of the WSM -- if you swap the wires 18 (G/R) to 21 (G/W) and 14 (W/P) to 15 (W/B) you should still have the same effect on the opposite side, if the issue is with the wiring of the lamps.
I'm not inclined to suspect a grounding issue if your system had been working fine just before you moved the relay. Dave Braun's idea about continuity is where my thoughts tend to be. Do your stop lights work properly? Those are the same filaments as are used for the rear turn signals. Bud
Bud Krueger (TD10855)

Bud,
The stop lights work fine. The parking lights work fine also. I found the old relay box, pulled the cover, cleaned the contacts, and wired it in with jumpers after removing the old(new) unit. It worked just like the present box-no lights on the right side. I've come to the conclusion that the ground path is okay, especially after you pointed out that the brake lights are on the same filament as the turn signals.
I'm going to go and try to switch the wires that you mentioned. I should say that after putting in the old relay box the ammeter showed a huge drawdown when the switch was turned to the right blinker and, of course, no flashing took place. Almost seems like there is a big short in the system to cause that much draw of current. Still don't smell any burning insulation yet! The left side still had the rapid flashing of the lights.
Will let you know what I find with the trading of wires.

Mark
Mark Strang

Mark,
I had the same exact problem. John Scagg gave me the solution. One of my front lights had a fixture that took the type of bulb where the two little studs on the side of the base were directly opposite each other, not staggered one deep and one shallow. As a result you could put the bulb in, in two ways each 180º away. There is an electrical difference in the filaments to cause this problem. All I had to do was reverse the position of the bulb and the problem was solved. Check closely and see if this pertains to you.
I spent several days of trouble shooting including grounding the heck out of everything I could find. The solution was especially embarrassing because stamped on the base of the bulb was "TOP". Duh!
Mort
Mort TD 1851

Bud,
Went out and changed the leads that you mentioned. Now I get no lights on either side but the dash light comes on and I get the rapid flashing of the dash indicator light. I'm at a loss. The only other thing I can guess at is that the flasher can is bad. I just can't tie that in to the right side lights not working, however. Seems to me that if the can works in one direction, it'll work in the other direction also.
A summary of findings seems to indicate that the ground path is solid since all lights work and the brake lights function properly. The same conditions are evident after changing the relay box to operate the opposite lights except the lights now don't work at all. A second relay box (the old box) with cleaned up contacts has yielded the same results, suggesting that the box is functioning correctly. Contact seems to be solid in the relay box from visual exam while turning the lever in either direction. There appears to be a short in the flasher system somewhere to cause such a major draw of current in the right hand position. The bulb filament can't draw the ammeter needle all the way to the left by itself. Don't know where to look for a short since everything checks out okay. Would have to be in the turn signal circuit proper I suppose. Perhaps a front side marker light since the brake lights work?

Mark
Mark Strang

Bud/Mort,

I think that Lucas struck me. I removed each parking light bulb, checked it out to make sure it was in correctly and reinstalled them. Then I tried the flashers. They worked! I came in and saw Mort's note. Mine were in correctly with "top" in the top postition when I removed them so I guess they were in properly from the start. Thanks for your help although I still don't know why they didn't function properly after moving the relay box 2 inches!
Now I'll check out the "new" relay box and if it functions correctly, I'll install it.
I hope that I don't have to live a life of little things that don't make sense while owning this car. It sure is a fun car though.
Thanks again,

Mark
Mark Strang

Puzzling. There is nothing in the directional circuit to lead to a high current draw. I have a drawer full of flashers that I went through to find the right one to use in Lazarus. One of the things that I would try, before swapping the flasher, is to unground the flasher. Its circuit should be totally floating.
I'd suggest that you make up a test probe that has an automotive fuse holder between two lengths of wire with clip leads on the ends. A 5 amp fuse should be fine for testing virtually any circuit in the car. If there's a short circuit -- the fuse will blow before any damage can be done to your wiring.

You could then connect one end of the probe to a source of 12 volts (polarity doesn't matter). The inspection sockets on the dash panel are handy.

You can prove out the relay/wiring end of the system by connecting 12 volts to terminal 1 of the relay and the touching 12 volts to terminal 4 to see the left side light up and terminal 8 to see the right side. If the appropriate lamps light up you'll know for certain that the problem is flasher related. Bud
Bud Krueger (TD10855)

Bud/Mort,

I can't stop thinking about this recent problem. There has to be cause. In thinking about it, I can't believe that the underdash shield was the problem. A path has to be in place for the turn signals to work. I think that the bulb on the right side must have not been tightly in the socket, therefore the circuit was not complete and the system effectively saw an open path. It was just coincidence that the turn signals failed. At least I can rationalize the failure this way and not blame Lucas. I can blame myself for not inserting the bulb properly. I'm letting Lucas off the hook on this one.

Mark
Mark Strang

Bud,

I'm confused too regarding the high current draw. It is odd that when I removed and reinstalled the bulbs that everything was okay. I had the flasher can hanging from the wires so it was not grounded. Could the wiring in the side lamp housing been touching ground so that when the indicator was activated the circuit was going directly to ground instead of the filament and when I removed the bulb, the slight movement of the bulb base came away from the short/ground? If that is the case I better have look at the connections in the lamp assembly. It's a tight fit to get everything in the housing and then get the bolt lined up and attached to the lamp base but it might be worth it.
Mark
Mark Strang

Make sure the harness isn't chaffed through where it enters the hole in the fender or housing, or where the retainer clip holds it up underneath. Could there be a sliver of wire that missed the spring clip/hole thing that is touching the socket/bulb or housing? Just random possible thoughts for causing a short.
George Butz

George,

I went back at it and decided to install the new box and button the whole thing up after I had inspected the side lamp which seemed okay. Hooked up the new box and it wouldn't work on the right side. Hooked up the old box and all worked well. Tried it again and had the high current problem take place again. Disassmbled the side light again and no problem. Everything worked well as before. I got curious because the lamp worked great without a ground on it just sitting on the fender on top of a rag. I then added a temp wire to the socket wire (green w/white) and got the high current draw to occur when touching ground. So, if the switch is moved to the right the current draw is high because the amperage is being fed directly to ground thru the system instead of the bulb and the bulb doesn't light up. That explains why I get a high current draw on occasion. Now I just have to figure out how this all relates to the ground. It would seem as if sometimes the hot wire goes to ground. Also where is the ground for the side light actually being made? To your point, it could just be sliver of wire somewhere touching ground once in a while. The area where the wires go thru the fender are solid with no fraying, etc. I've had it for the day. Time to get this off my mind for awhile.

Mark
Mark Strang

Mark, if your lamp worked great "without a ground", it was actually finding its return path through other bulbs in the lighting circuit. I suspect that, if you remove the lens from the lamp socket, you'll see that the side lamp filament is lit. You may even notice that your tail lamps are glowing. The current path is from your G/W (21) wire, through the socket base into the side lamp filament, out through the Red (41) wire and from there through all of the lamps connected to the Red (41) wires, i.e., the running lamps, tail lamps, number plate lamp. It sure sounds like a wiring problem at your right fender lamp. Good luck. Bud
Bud Krueger (TD10855)

Is the socket new or old? There could be an internal short? If you remove the lamp and socket, you should have no current draw- this would rule out a short somewhere in the harness. Check the socket assembly for damage/cracks, etc. as well. Take a meter ( or test light or something), and make sure no continuity between the hot teminals and the base. The base should be the only ground- through the bolt to the fender (see David DuBois's great article on grounding). Bud may be on to something as well- check that socket/area out as well. One more easy test: remove the light/socket. Take a known good bulb, rig up a groud wire, hold it on the brass outside baase, then touch the ts wire (G/W ?) to the terminal and try it. If it flashes and works fine, then you know the socket is somehow shorted. I think. George
George Butz

Bud/George,

I replaced the socket with a spare new socket. Still had the problem. Removed the 41 wire and the light didn't go on. Put a jumper to the base of the socket and the light went on and flashes as it should.(I'm doing this work with the light assembly just resting on the fender so there is no bolted ground. Makes for easy easy testing.) Now it appears as if the problem, whatever it is, is not in the 21 wire. It tests good with no problems.
I then disconnected the 41 wire at the back of the car from the tail lights thinking that perhaps this wire was causing the problem. The problem still was there. My guess now is that the problem is somewhere from the 41 wire at the socket thru the side and headlamp switch, since removal of the circuit beyond that has no effect on the system. Does this sound reasonable and if so, what do I look for?
This sounding like one of Ed Haskel's posts that just keeps going on!
After pondering this note I just looked at the diagram again and noticed that the 41 wire goes to the right marker light also. I'm going to examine that socket as well and see what it looks like.
Mark Strang

Hi Guys,

Well, I just removed the left marker light and have determined that it too functions exactly like the right side. In other words, the directional signals on either side need no fender ground to operate correctly! The ground is being provided for both of the lights from the 41 wire. By the same token, the parking lights are being grounded by the directional lights. I'm a mechanical type, not an electrical. Don't understand electrons, and especially grounds, but I do understand hand signals. Think that I'll just button it up and write this one off to Lucas.
Mark
Mark Strang

There is a great Lucas trouble shooting guide- go to www.fromtheframeup.com , click on the "Lucas Technical" tab, click on Section 8, go to pg. 57. George
George Butz

Mark
I think we all feel your pain...been there, done that!
The Prince of Darkness can be an unforgiving foe.
Edward
E.B. Wesson

I won the battle with the Prince of Darkness! It turns out that I had a bad new relay box and a bad fender socket and no grounds on the fender lights on top of just being dumb. Cleaned up the contacts on the old relay box, made solid grounds, replaced the marginal socket, and the turn signals worked fine. I took out all of the light bulbs in the back and pulled the snap connector apart at the rear for the 41 wire. No ground. Stupid me forgot that the bulbs have to have a path for the electrons to go thru. The bulbs provide that path!

Relocation of the relay box for the installation of the underdash shield must have caused the box to have a problem. Glad that it showed up now. I learned a lot and got a couple of potential problem areas addressed now instead of later.

Thanks for all of the input.

Mark
Mark Strang

Hooray!!! Good for you, Mark. Bud
Bud Krueger (TD10855)

This thread was discussed between 10/05/2011 and 13/05/2011

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.