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TR4/4A 1965 TR4 Headlight Isssue

Hoppy_H

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I have a 1965 TR4 that's sits idle most of the time. I turned on the headlights and they came on very dim. I also noticed that the amp gauge went to full discharge. I looked at a wiring diagram and all I see is a "Lighting Switch" with three wires attached to it.I don't see anything like a relay. Does anyone think the lighting switch could be the issue? Where is it located? Under the hood or under the dash.

Thanks,
Hoppy
 

TR3driver

Great Pumpkin - R.I.P
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That's right, no relay originally (although some folks add them). The main headlight switch is behind the knob you pulled to turn them on; on a TR4 the dipper (aka dimmer) switch is near the driver's left foot.

Obviously, you have a short to ground somewhere. Could be at one of the switches (ISTR there is an unused tab on the main switch that is apt to short to the dash), but could also be anywhere else in the wiring to the headlights. When my TR3A suffered from that disease, I eventually found that a strand of wire had escaped from one of the bullet sleeves and was touching the body underneath.

One test you can try is to step on the dipper switch, to select the other pair of filaments and try the main switch again. If you still get the ammeter to full discharge, the short is somewhere between (or at) the two switches. If it goes away, then it is somewhere between the dipper switch and the headlights. Obviously you don't want to leave the switch on for more than a second or two; otherwise the smoke will start to leak out and you'll have an even worse mess.

Good Luck!
 

Geo Hahn

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At least the smoke might pinpoint the location of the short (just kidding).

I added relays to the lights on my TR4 when I happened to touch the backside of the switch body after a long night drive -- it was hot. I opened, cleaned and reassembled the switch but adding the relays seemed like the best solution. Headlights (esp if you have upgraded to something with a higher draw) are too much current for that switch to comfortably handle.
 

trrdster2000

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All, just a bit of information to help those who undertake a weak light problem. I worked on a TR4A a while back with yellow head lights. Changed to Halogen with only marginal improvement. Next the alternator conversion, some help there, on to the relay wiring kit from Vicky Brit, not your best option, but effective, (you need to cut wires to get them into the head light bucket. Remember to soldier them back together). A big help, but all may have been for little gain. Next was the strip mounted near all the ground connectors, under the grill, running across the front, using a idea from one of the forum members. One large ground wire to the clean and sanded frame attached to the strip and the bullet connectors cut off and wired to the strip. Now we have bright head lights.
The relay is a good idea to keep the heat away from the switch but I'm not sure if fixing the grounds may have done the trick to start with.

Wayne
 

TR3driver

Great Pumpkin - R.I.P
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Could it be as simple as dirty connections causing greater resistance, which would result in the high amp gauge reading and the dim lights?
Dim lights yes, high current no. More resistance means less current. The basic relationship is that current (amps) equals voltage divided by resistance (ohms).

Headlights can act a little weird sometimes because their resistance goes up when they are lit, but not in this case. The high ammeter is also why I don't believe it is a bad ground in this case.
 

Geo Hahn

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Checking grounds is always the best place to start. Are there 65 TR4s?

I believe a few 4s were built in January 1965 and in any case many 64 builds were registered as 65s. Mine was one of those but I got the MVD to make into a 64 when I titled it in Arizona. Reason was that Arizona permits year-of-manufacture plates and there was no AZ plate for 1965, just 64 plates with a sticker.
 
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Hoppy_H

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Thanks Guys. I'll get in the garage and see what I can find.

Hoppy
 
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Hoppy_H

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Update - I was going to try to eliminate this problem today and the lights are working properly now. I guess I will wait until they malfunction again to worry about it. Sure hope it's not while I'm on the road at night. I'll probably drive the car during the day with the lights on and test them.

Thanks for the help guys.
 

mrv8q

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Update - I was going to try to eliminate this problem today and the lights are working properly now. Sure hope it's not while I'm on the road at night.

In the far corner of Hoppy's garage, tucked back into the shadows, a deep, low voice rumbles, "MWHAHAHA".
 

TR3driver

Great Pumpkin - R.I.P
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Update - I was going to try to eliminate this problem today and the lights are working properly now. I guess I will wait until they malfunction again to worry about it. Sure hope it's not while I'm on the road at night.
Just a thought, you might want to try wiggling the wiring harness in various places, to see if you can get the problem to come back while you're looking for it, instead of while you're driving.
 
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