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TR6 1976 TR6 Ignition warning light

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BillyZ

BillyZ

Freshman Member
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Hello all you TR6 owners - I'm hoping someone out there can share their solution to the ignition warning light. I replaced the alternator yesterday as the old one was only putting out approx 13 volts. The new alternator has a charge rate of 14.3 volts. All was good until that ignition light refused to go out and happily glows at all rpm ranges.The car is my original 76 which got a frame off restoration by yours truely. None of the fuses are blown and battery cables are clean and tight - belts are new and have the proper tension. Any thoughts would be greatly appreciated - Regards BZ
 
Is your battery also new? Might have a dead cell.

Check all your connections behind the dash as well.

Bill
 
Is your figure of 14.3v a measurement you took "after" the charge light decided to stay on or "before"?
 
If that light is on, chances are extremely high that there's a fault in the alternator.
It could be lit because of some wiring or battery fault but I doubt it./ubbthreads/images/graemlins/cryin.gif
Assuming you just bought it either new or reconditioned, I would take it back from whence it come, and have them bench test it./ubbthreads/images/graemlins/hammer.gif
Let us know how you get on.
 
Yesterday installed rebuilt Alt from Roadster factory - no change, Today @6pm installed rebuilt Alt from Moss no change. No fuses are blown - have pulled all fuses to isolate circuits with no luck - all gauges work, exterior / interior lights ok. battery is less than a year old and I gave it a full charge before reinstalling. If there is a wire falut somewhere I can not seem to find it. Regards BZ
 
Re: 1976 TR6 Ignition warning light

14.3v is good. Succinctly, the charge light is in series from the ignition switch to the field coils on the alternator. The current flowing through the lamp energizes the field coils until the alternator gets up to speed and starts making electricity. Once the alternator is up to speed the charge light wire connection on the alternator goes to the same voltage that the alternator is putting out... so both sides of the lamp should be at 14.3v (in your case). If you hadn't said you had 14.3V AND that you've tried other alternators... I'd suspect the diode trio in the alternator.

Have you done anything "funky" wiring up the charge light or is it a stock Lucas configuration? Somehow the lamp is still getting a path to ground. Use a volt meter and hook one of its terminals to chassis ground, then use the other probe to measure the voltage on the charge light wire (small wire) connection on the alternator. As mentioned in the last paragraph, this should read 14.3v just like you measured at the battery. Post back with the measurement.
 
Re: 1976 TR6 Ignition warning light

Doug, the wiring harness is stock replacement 8 years ago during restoration never had any problems until now. However today I took a good look around the engine bay and discovered two of the small wires from the harness to the solenoid had been subjected to some extreme heat enough to burn the plastic covers on the metal female connectors. If the starter relay is bad would that create the problem I'm encountering with the ignition light staying on? Regards BZ
 
Re: 1976 TR6 Ignition warning light

The starter wiring should be pretty far removed from the charging circuit... but never discount Lucas gremlins.

The first thing I'll suggest is something you may have already done. Take the alternator off the car and to a parts store like Advance or AutoZone where they can bench test it for free.

While the alternator is out of the car, try ohming out the charge indicator light wiring... looking for a ground connection. There shouldn't be one with the alternator removed. IF somehow the overheated wires in your harness have fused together, it could be that the charge light circuit has found another path to ground. It may be a path through something like a wiper motor, headlamp... who knows. If (with the alternator removed) you measure anything other than INFINITE (open circuit) ohms between the disconnected charge light wire at the alternator and chassis ground... there's a short somewhere.
 
Re: 1976 TR6 Ignition warning light

Today - charging voltage from the alternator to the battery = 14.3 Volts @ 1000 RPM - voltage @ the harness for the ignition bulb @ 1000 RPM = 14.07 volts .23 volts difference? BZ
 
Re: 1976 TR6 Ignition warning light

Is that 14.07v with the lamp disconnected from the ignition switch? Regardless, the lamp should be "OFF" with that voltage as the difference (as you pointed out) is only 0.23v which isn't enough to light up the lamp.

If you turn off the car and the ignition, you should be able to safely unplug the alternator from the harness. If you connect one side of your ohm-meter to ground and probe the small female lug in the alternator plug... you should get nearly infinite ohms (No connection to ground). Have you tried this yet? Have you had a chance to take the alternator to a parts store for bench testing?
 
Re: 1976 TR6 Ignition warning light

Alternator off to the shop for bench check - I did the ohms test you recommended. Ignition off - battery cables connected - probed the small brass connector[ wire "Brown & Yellow"] on the plastic alternator connector went to ground got a reading of 9.3 Ohms?? BZ
 
Re: 1976 TR6 Ignition warning light

It sounds like you've measured what I was talking about (brown/yellow wire to ground with the connector unplugged from the alternator).

From memory, in Lucas wiring, the brown/yellow goes from the alternator to one side of the charge indicator lamp. The other side of the lamp has a white wire that goes to the ignition switch. I think the same switch connection has the white wire that goes to the coil. SO, if your points are closed and you measure the brown/yellow to ground, you could be measuring the resistance of your coil and the lamp in series.

I'll check my car tonight and tell you how it compares to your 9.3 ohms.
 
Re: 1976 TR6 Ignition warning light

Well, I measured the brown/yellow wire on my car as I instructed you to do and came up with something close to 7.5 ohms with the points "closed". If I open the points things start to change but the readings aren't stable. Looking over the wiring, the white wire from the ignition switch that feeds the warning light also feeds the coil and my electric fuel pump. All these things "being there" change the readings. However, since neither of us measured a dead short, I'd say your warning light wiring is intact. Based on that suspect the problem is inside your alternator.

One additional check. with the plug removed from the alternator, switch on the ignition. The red lamp should be "off". If, with the ignition on, you ground the brown/yellow wire the warning light should turn "on". If this happens, the problem must be internal to the alternator.
 
Re: 1976 TR6 Ignition warning light

Got the alternator back from our local generator repair shop Alt checks out OK. Reinstalled Alt back into car hooked up all elec connections - started car ign light NOW OUT when running?? However I took another voltage reading from the battery = 14.04 volts which is closer to the 14.07 volts I measured at the Ign light. I'm at a loss to explain why or what happened here? BZ
 
Re: 1976 TR6 Ignition warning light

I can't begin to guess what's going on. However, the two readings should be close together like you now have measured. I hope this is the end of the problem for you. All I can suggest is that somehow you had some interesting ground problems... but those should have kept the light "off" not on. Let us know what happens.
 
Re: 1976 TR6 Ignition warning light

Thanks Doug and eveyone else for their input to this problem. Took the car for a ride yesterday and so far so good. I just wish I new what caused the problem in the first place. Thanks again - BZ
 
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