- My model of MX-5 is: 1990 Eunos
- I’m based near: Suffolk
- I’m looking for technical help or recommendations on: rear lights cutting out
Hello all, in my 1990 Eunos sometimes when I put the headlights on, the dash doesn’t illuminate, my rear lights don’t come on, and my front small driving lights are off too. The headlights and high beam both work. Sometimes this happens after the lights have been on for a while for no apparent reason. I’ll be driving along at night with the lights up, then suddenly the dash goes dark and the people behind me lose sight of me.
To get everything to work again, I usually have to flick between high and low beam several times, or turn the lights off and on again a few times. Not ideal when on the motorway at night!
Does anyone know what might be causing this to happen? And what can I do to resolve it? Many thanks.
Is there anything aftermarket fitted, have you checked for a dodgy fuse? sounds like an earth fault.
M-m
First check the inside fuse box; there will be 2 10A fuses covering the rear and meter lighting. Its obviously no blown, but its it fitted properly; pull the fuse and check the board for any signs of damage due to arcing (burnt plastic etc). Some Japanese aftermarket accessories also use dodgy looking connectors going into the fuse positions.
Translation of the Japanese fuse cover (or if its missing, which is often the case)
As its a Eunos Roadster, check the wiring for the rear fog light switch. To the right of the steering wheel, you will have a row of mostly switch blanks. You might have a factory or aftermarket switch here for the foglight. Ignore that for the moment, but check the blanks; you are looking for a blank with a small blue connector block running into it; this is for an optional dash dimmer switch. If the connector isn’t fitted properly into the “blank” which is actually a jumper, the rear lights/gauges fail. This wiring is often tapped into for the rear fog light. Check its all sound; if you jiggle the wires, does that affect the function.
Then check the TNS relay. This is located under the front passenger wing, towards the back of the engine bay. There should be a cover I think, then you find 3 relays.
Pull the relay, check for obvious damage, refit, does jiggling or tapping affect function (many years ago, I had an unrelated issue related to a Roadster randomly cutting out during driving. In the end I got an auto sparks in, and even then, he only accidently diagnosed it while he was fiddling around with the main fusebox, and replicated the issue when he screwdriver fell on a relay. The relay in question controlled fuel injection, and upon further inspection, was marked “Ford”. The part number on it was for a Ford Probe. Took the relay apart, and it was rusted inside. New relay needed.).
If all that checks out, then either the main headlight switch, or, as the previous poster suggests, the rather tedious process of checking the earthing points, starting with areas that someone has made some changes to.
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Thanks both, I’ll do some investigating over the weekend.
I had a look at that blank switch yesterday while changing a fog light switch, coincidentally. I will check it again to see that it is connected properly. I was wondering what that blank switch was for, I wasn’t expecting anything to actually be running to it. If I buy the dimmer switch and plug that in, will the dimmer just work or is any additional wiring required?
I was planning on using the blank for when I eventually wire in a rear screen heater, but if it is a plug-and-play job for the dimmer I may as well use it.
A Mazda dimmer will work. I think while the NA was wired up for a dimmer, it was never used in most markets, only the US. NBs have a dimmer, and I think the switch will work perfectly (except in very late NAs. It did in my older NAs, but not in my newer NA). NB dimmer switches have a matt finish. A lot of the so-called NA dimmer switches came out of old popup headlight 323Fs in scrapyards. I suspect they are mostly gone now.
Checked TNS LA10 relay, checked fuses in interior fuse box, checked wiring to the aftermarket foglight and the dimmer switch. All ok, none of it affects the lights when they’re off or on when they’re jiggled and prodded, so they all seem ok.
The only thing left I think is the main combination switch on the light stalk. Jiggling the stalk between low and high beam is how I get the lights to come back on, so presumably it’s a bad connection in that switch somewhere?
Haven’t checked earths yet, but as everything else electrical is ok I assume they’re fine. I’ll order a new combo switch probably and see if that does it.
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Hi Toby. Did you manage to solve this as I’m having the same issue? Thanks.
