Wierd headlight problems, need a pro diagnoser

[supralicious]

Ok so I have an 89' Mx-5 which has had this problem since I got it.

Basically, one headlight works, then the other is very dim. If I switch to high beams, the one that's bright gets brighter and the other stops all together. I bought brand new headlights and bulbs and it was exactly the same. I noticed the RHS headlight connection at the rear, was corroded badly so I patched that up as best I could and it made a good connection - same problem.

I opened it up again today because the lights had stopped all together. I re-established the connections on both sides and bam, then the RHS was really bright and the LHS stopped working all together. Went over and jiggled the LHS connection, now the LHS is really bright and the RHS is dim.

So I hope that all makes sense but yeah, it seems almost as if there's not enough power to light both up. /shrug So what do you think the problem is? Replace both plug connection behind the headlights? Relays?

Thanks guys, let me know if you need more info.

[93_Clubman]

Is the above with the engine running or not running?

[supralicious]

Not running... anticipating your next question I'll run out and see what it is with engine running.

[supralicious]

Same with engine off or on.

[Mr Morlock]

it is probably poor connections somewhere and that can either be power or earth wires or both. Connections can be cleaned eg emery paper. Terminals can be cut off and replaced if really necessary though you do need a crimping tool and terminals.You can check connections with a multi/voltmeter or for power leads with a simple circuit tester which lights up if power is transmitted. Keep fingers well clear of pop ups. For checking processes you can check the net for info.

[supralicious]

I think you might be on the right track. General wear and tear on the wires is my best considering the really high kms and age of the car. Might be an auto electrician job. =/

[RawSouth]

To me that sounds like a dodgy earth connection.

[supralicious]

To me that sounds like a dodgy earth connection.

Could you elaborate more on this and how I might check for it?

[RawSouth]

Here is a link to the wiring diagram for a 91 NA...

http://www.mediafire.com/?mn1mzmmbknw

The wiring diagram you are looking for is on page 3. You can try continuity testing the relevant wires using a multimeter.

You can test the resistance of earth connections by measuring the resistance of the joint (measuring between 'before the joint' and the chassis), ideal earth connections should have (almost) zero resistance

[Benny]

If it's a problem with your connectors, you can just cut them off and replace them with simple spade connectors.

My headlights have been connected just using spade connectors fo rthe last couple of years, and they work fine.

However, it does sound like an earth connection problem to me.

[supralicious]

If it's a problem with your connectors, you can just cut them off and replace them with simple spade connectors.

My headlights have been connected just using spade connectors fo rthe last couple of years, and they work fine.

However, it does sound like an earth connection problem to me.

This was pretty much on the money.

Ended up just cutting off the one of the old connectors and replacing it, on each side. Seems like the one on the right (if your looking at it) is prone to shorting out, as it was melting the plastic around it and so-on. Now all is fixed and working fine. Although the high beam light still stays on... /shrug. Still, I'm happy.