Ignition warning light problem

[andyf]

I feel that I should know the answer to this but I don`t, so here goes.

I fitted a recon alternator just over 12 months ago when the bearings went in my old one. The issue I have now is that the ignition warning light does not light up when I switch the ignition on, but glows intermittently during running. The voltmeter shows ok volts although it reads quite low (just above red) when the light is glowing but rises when it decides to go out. The car starts fine without issues.

What`s wrong do you auto electrical specialists think?


1980 Persian Aqua DHC

[TR Tony]

Has it done this ever since you changed the alternator Andy, or is this something that has just started?

When you switch on the ignition, 12V is supplied to the warning light from the battery via the ignition switch, the other side of the light connects to the alternator. Before you start the engine the alternator is stationary so not giving any charge - the warning light earths through the voltage regulator in the alternator & lights up. When you start the engine, the alternator also feeds 12V to the warning bulb so the bulb gets 12V from both sides, thus it has no earth & goes out.

Normally if the light does not come on when you turn on the ignition, I would check the bulb first. However, you say it glows when running therefore the bulb itself must be OK. So, either it is not getting the 12V from battery when you turn on, or it is not earthing via the alternator.

You mention that sometimes when running the voltage reads quite low, & the light glows, but then the voltage will rise & the light goes out.

Check all the connections at the alternator are clean & tight. Check the battery connections. If all this is OK then since the warning lamp earths through the voltage regulator in the alternator, I would suspect the regulator may not be working properly, which could also account for the variation that you are seeing in the voltmeter.

Tony

<font size="1">1981 TR7 FHC Cavalry Blue
1980 TR7V8 DHC Jaguar Regency Red - sadly sold!
1977 TR8 FHC EFI Factory development car Inca Yellow</font id="size1">

[Workshop Help]

In my pumpkin patch, all the auto parts stores provide a FREE testing of alternators, starters, batteries, and basic life philosophies. Is it same way where you live? If so, waste no time in meandering over the hill past meadow and farm to your local favorite emporium to have your's tested.

Now, if you'll excuse me, the Mighty TR7 is going out on a couple of work appointments to earn it's keep, which is what it was designed to do.

Mildred Hargis

[andyf]

Thanks for the replies. Tony, I don`t know whether it has done it since it was fitted because I did not drive the car until May of this year due to developing a blood clot in my leg. It has probably been doing it this summer although as I tend to drive with the top down when I can I must be honest and say I haven`t really noticed the light [:I] (although I had noticed the erratic voltmeter).

Mildred, sadly those sort of auto stores are a distant memory around here, ours are generic national chains, where you can buy anything for your car as long as it is a stereo, or random shiny stick-on bits with Ripspeed written on them. I doubt most of the staff would know what an alternator was, let alone how to test it.

Edit: Forgot to mention, I have replaced the connectors on the back of the alternator, checked battery connections and even put a jump lead on the alternator body to battery earth to no avail.


1980 Persian Aqua DHC