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Re: TR7 No Cranking Problem

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William Smith

Re: TR7 No Cranking Problem
« on: October 08, 2017, 03:58:43 PM »
Thanks to everyone who responded. I received a number of great suggestions - some about checking things that I didn't even know existed. I'll keep you posted on how I make out.
Thanks again,
Bill Smith


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"Jim Altman"

Re: Re: TR7 No Cranking Problem
« Reply #1 on: October 08, 2017, 04:23:43 PM »
I have had two starter relays go bad in the last six months, so it'scertainly something to check.  It was one of the contacts, so I could hearthe relay click, but nothing happened.  The relay inside the fuse area, soyou may not hear it unless you have glovebox open.  Sometimes turning thekey to start repeatedly would make it make contact and the car fired rightup.Jim Altmanjaltman636@gmail.com

Dave

Re: Re: TR7 No Cranking Problem
« Reply #2 on: October 08, 2017, 04:54:31 PM »
And of all the relays on this car this is the one that is not your standard form C relay where you can get any old replacement from your FLAPS.  This one looks the same, has the same number of terminals but it works a little differently.  Instead of having a Normally Open, a Normally Closed and  Common contact it has two Normally Open and a Common contact.  When energized it connects all three together and when de-enegized all three terminals are disconnected from each other.This one has a different color than the others.  Dave Massey

Ira

Re: Re: TR7 No Cranking Problem
« Reply #3 on: October 08, 2017, 05:01:41 PM »
Hello Dave,



Sunday, October 8, 2017, 1:53:46 PM, you wrote:

dave1massey

Re: Re: TR7 No Cranking Problem
« Reply #4 on: October 08, 2017, 05:07:59 PM »
True.B  If you have some wire, terminals and crimpers.B  I got all that but not everyone does.









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"Jim Altman"

Re: Re: TR7 No Cranking Problem
« Reply #5 on: October 08, 2017, 10:33:54 PM »
Looking at the schematics, that second terminal on the relay where all three

are connected together is only in use on the FI cars (as to TR8's, didn't

check TR7 schematics), so it should work with a "normal" relay for the

carb'ed cars.





Jim Altman

jaltman636@gmail.com

Dave

Re: Re: TR7 No Cranking Problem
« Reply #6 on: October 09, 2017, 07:25:37 AM »
I noticed that, too.  However, when I pulled my TR7 manual and looked there both are used.  One contact is for the starter solenoid and the other is used to light up the brake warning lights.  The TR8 key switch has a special contact used expressly for the latter and the other contact goes unused.



What is not clear on the diagram is which contact is used for the starter.  If it is the contact in the same position as the NO contact on the standard Form C relay they you can use one of those but if it is the other contact you can't.  For that reason I cannot recommend using the standard Form C relay without further investigation.  And that is for the TR8.  The TR7 REQUIRES the special relay.



 



 



Dave Massey

Greg Gall

Re: Re: TR7 No Cranking Problem
« Reply #7 on: October 09, 2017, 11:08:27 AM »
I can confirm that the TR7 requires the special starter relay...







Years ago I bought a dead 1977 TR7 and it had no power to the ignition system. I found that the beureka wireb (resistive wire) which acted as a ballast wire to power the coil was fried. The moment I patched it and turned the ignition to ON (not START), the car started turning over and the eureka wire started smoking!







Turns out that the previous owner had replaced the starter relay with a normal Bosch relay and now the coil positive was electrically connected to the starter solenoid!







So I recall that the TR7 starter relay also functioned to bypass the eureka wire (ballast resistor) only when the key was in the START position (hotter spark during starting the car). Using a regular relay forced power to flow from the positive side of the coil to the starter solenoid, which activated the starter as soon as the ignition was ON and fried the eureka wire within probably a minute! Since the eureka wire runs through the dash wiring harness, you would have to pull the dash to repair it and there is a high probability that other wires will be damaged as well.







So the moral of the story is DO NOT replace the starter relay with a standard one, at least on a TR7!







Incidentally, I have owned a couple TR7bs (besides this b77) with failing starter relays. As Dave says, there is a big inductive load that tends to arc across the contacts. One car I carefully opened the relay and cleaned the contacts (they were rather burnt looking) and the other I just kept a screwdriver in the glove box and would hit it the relay with the handle any time it acted up... :)







Greg



Calgary







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