TR6 TR6 wiring help needed

[tdskip]

So the sorting out of the '74 TR6 continues.

She has a wiring fault that is driving me batty - she'll start fine and then next turn of the key she'll not do anything. Totally dead. Sometimes when I disconnect the battery and the re-connect it she'll fire up like usual, next time, dead again.

When she is totally dead, there is no noise at all. No clicking from the starter, just dead air.

Battery is fresh, charged, and has a good ground.

The only thing I changed recently - and she did this <span style="font-weight: bold">before</span> I made any changes as well - was to change the points and condenser.

When she does turn over there is no spark at #1 plug or at the coil to distributor plug wire. The starter spins just fine when the power 'connects'.


This maybe be unrelated, but the reverse indicator switch pictured here is loose - the wiring diagram indicates there is a 'neutral safety switch - but I'm not sure if that would kill the power. I ask because one time when the power was dead I jiggled that switch and made sure the loose wires were not touching metal and she started. Could have been a coincidence...

Help!

 

[TR3driver]

Well, a 74 would have had that weird seatbelt starter lockout module ... what have you done to bypass/eliminate that ?

If your DPO just twisted wires together under the seat, that might be the problem.

 

[tdskip]

Hi Randall - I do not have a good history on the car.

The wiring for those is currently disconnected - so that could easily be the issue. I fonud and labled those wires last night.

Any tips on how to properly bypass or disable those?

 

[tdskip]

NEWS FLASH!

Based on your hunch Randall I found and disconnected one of the seat belt 'sensor' connections (top right in bottom picture) and I have power again.

The engine spins over just fine now BUT I'm still not getting any spark.

 

[mrv8q]

TD, I tackled this problem 2/07/07, and here's a post answer from TRopic6:

Welcome to the world of the '74 TR6, where starting depends on the whims of the dreaded Seatbelt Module (SBM). To meet US regulations, Triumph inserted a Starter Relay between the IGN switch and the starter solenoid. The Starter Relay is controlled by the SBM, which used early 70's technology in electronic logic to decide it should let you start the car, depending on seat and seatbelt sensors.

Open the hood and listen/feel for a click in the starter relay as you try to start (the starter and horn relays are mounted together by the fusebox) If it does not click, the SBM may not be passing 12V to it. Using Don Master's excellent diagram, you'll see the SBM is the 12-pin device at the bottom middle. 12V from the IGN switch goes in at pin 11 on a white/red wire and hopefully out at pin 12 (white orange) and on to the starter relay.

Do not use a short piece of solid copper wire to jumper those two sockets. This would completely bypass this important safety feature (that was changed to a buzzer/light for '75). If the relay does click, check that it's sending 12V to the starter solenoid (big White/Red wire). I kept having problems with the Lucas relay so I replaced it with a headlight relay. I've had no problems since, but then I also rebuilt the starter and dismantled the solenoid and cleaned the contacts. Also, check the connections where the IGN switch connects into the main harness.

Again, I jumpered the 11 and 12 wire, cleaned the starter relay, and completely disassembled and cleaned up the fuse box, and I had ignition. Poke around the posts from 2.7.07, "'74 ignition woes" for more info..... Good luck!

 

[TR3driver]

Do not use a short piece of solid copper wire to jumper those two sockets. This would completely bypass this important safety feature (that was changed to a buzzer/light for '75).

Hopefully, it's obvious to all that that was tongue-in-cheek ... although I agree only to the extent that IMO it's better to splice the white/orange together with the white/red; rather than take a chance on the short piece of wire not making good contact sometime in the future.

No spark at the coil is likely a different issue ... have you checked for juice to the coil ? Then that the point side of the coil switches between ground and 12v as you turn the engine ?

Assembling the points wrong (creating an electrical short such that the coil terminal is always grounded) is a VERY common mistake. The wire goes UNDER the insulator, not on top of it.

 

[tdskip]

Ok guys - found the Seat Belt Module on the wiring diagram. Where on the physical car should the darn thing be located?

 

[tdskip]

Um, so, like I totally grounded the points juts like Randall suggested. I'm blaming it on the 1.5 year old who was helping me.

Went to try it, no power. Disconnected both the + and - battery posts, reconnected them, and she started.

My TR6 manual doesn't have a picture or location of the Seat Belt Module, only references the buzzer, so if anyone has a picture let me know. Thanks!

 

[mrv8q]

The SBM is under the glove box, about the size of a pack of cigarettes, w/a 2 inch round connector sticking out of it.....

When I first got my '74, it started (seemingly) fine at the DPO's home. When I got it home, it wouldn't start 9 out of 10 times. Among the other problems, the switch back was loose; one of the tangs was broken, leading to the intermittent problem. One more thing to check!

 

[TRopic6]

TD,

Just got back from the Arizona Memorial where they rang the ship's bell and had a seminar with 5 Pearl Harbor vets. They told it like it was (and it was rough).

Here's some shots of where the SBM is (passenger footwell, upper left side and what you can do. Jumpering the thing will defeat the neutral-to-start safety feature, so you'll have to use the same care as in your TR4! As Randell points out, a better solution would be to splice them up near the starter relay. This was a quick fix to get the car running after 26 years.

The original owner of this yellow 74.5 said the thing had starting problems from almost Day 1 and the dealer ended up disconnecting all the seat & seatbelt sensors.

 

[tdskip]

Thanks guys - this is a HUGE help. Found the unit.


Kevin - I am guessing that the picture you posted is how it was before you jumped the connection like in the picture immediately above?

With the unit 'jumpered' like above I am assuming you leave it completely disconnected at that point except for the copper between 11 and 12.

Thanks guys!

(FYI - after my dumb bunny move on the points I finished the tune up and she is running great now. Balanced the carbs and adjusted the timing and she starts immediately and is really smooth. Weird, I'm not used to one of my cars behaving like that - lol).

 

[mrv8q]

Kevin - I am guessing that the picture you posted is how it was before you jumped the connection like in the picture immediately above? With the unit 'jumpered' like above I am assuming you leave it completely disconnected at that point except for the copper between 11 and 12.

No, just the opposite, that's how I'm running it now.... as best as I recall, the orange wire runs across the back of the instrument panel, and to a terminal on the starter relay.... going from memory here. I had help from one of the local TR electrical gurus. (And no, not our guru Randall!)

 

[tdskip]

So you jumped the connection and re-installed it into the receptical?

 

[TRopic6]

Aloha tdskip,

I run it with 11 & 12 directly connected and the plug out; crude but effective. The white/red wire from the "start" post of the ignition switch is routed right back to the starter relay via the white/orange wire. There are more elegant ways to do it but that will work while I'm running the bugs out of a car that sat for so long. Unfortunately this eliminates the "gearbox in neutral to start" feature, which is a good thing.

Looking at Don Master's wiring diagram, looks like the '76 TR6 didn't include the SBM in the starting circuit. I guess the idea proved too far in front of the electronic technology of the time!

Jeff
74 & 74.5 TR6

 

[tdskip]

Aloha Jeff - and thank you for your help (and for making the effort to pay your respects at Pearl Harbor. Hearing from those Vets must have been something).

Crude but effective sounds fine to me at this point!

 

[mrv8q]

So you jumped the connection and re-installed it into the receptical?

Yep! Good luck!

 

[tdskip]

Success! Jumped the wires as shown and she starts on command now.

Guys - I <span style="font-weight: bold">really</span> appreciate the help and info.

I'll add this latest round to the 'beers owed' tally.

Thanks!