Bad BCM?

[Guest wayne2reattas]

I have a 88 Reatta. I have had trouble with the wire that connects to the switch module burning/melting.It is melting the harness clip and the back of the switch.

I pulled both headlights and found frayed wires caused from headlight doors opening and closing. I repaired all of those wires. Then put in a new hi beam and low beam relay. The lights come on but after a couple minutes the yellow wire and the top of the switch module get extremely hot.

Has anyone gone through this before? I would really appreciate any advice... Thanks

[Guest Greg Ross]

Wayne,

If the headlights go on and off, and the headlight doors open and close on cue then the BCM is lilely fine.

Heat is a a bi-product of high resistance, either the terminal pins/ sockets in the connector are bad or the switch module itself has poor or dirty/ carboned up contacts.

I would pick up a replacement Headlight switch module and try that. Having to splice on a replacement harness plug end would not be very pleasant!

ps I recall replacing a headlight switch module that was starting to exhibit the heat effect symptoms. I can almost date that experience, it was in the hotel parking lot in Buffalo, NY in July, 2001? before departing the BCA to head back to the east coast.

[Guest wayne2reattas]

Greg,

Thanks for the info BUT this is the third switch module I have had to splice in. After finding the frayed wiring at the headlights , then repairing that I spliced in another switch module. Then that one burned, So I replaced the relays both hi and lo. The lights do come on and off as they are supposed to but then the yellow wire gets very hot and starts to melt the harness and switch.

If you have any other thoughts about what I can check I would REALLY appreciate it. Thanks again....

[Guest wayne2reattas]

Sorry I meant that I had to splice in two harness plugs not switch modules!

[Ronnie]

I would isolate the circuit that is causing the problem. Start by disconnecting circuits going to the headlight switch, headlight, tail lights, interior lights, anything powered by the headlight switch, until the yellow wire stops overheating. Then troubleshoot the circuit that causes the wire to overheat.

I suspect you have a wire somewhere partly grounded OR possibly a bad ground that is using another circuit as a ground (back feeding through the headlight switch).

[Guest wayne2reattas]

How do I go about isolating the circuits? Would I pull fuses or breakers for particular circuits? Thanks for the response. Makes ALOT of sense to do it this way. Thanks.

[Guest wayne2reattas]

A few weeks before this problem started I replaced the regular headlamps with Sylvania Silver Star high performance halogens. Could that be causing this problem?

[Ronnie]

Start out by disconnecting the new headlamps, one at a time. Did the wire stop overheating when either one was disconnected? Next disconnect the headlight motors. Did the overheating go away?

[Reatta45]

Get a DVM with a DC amp clamp, (around $75.00, but will last you a lifetime)… much easier to see exactly what the amp flow is, than interpolating from wire temp. KennyV.

[Guest wayne2reattas]

The wire gets very hot as soon as I put the Hi Beams on. With just regular headlights on the wire doesn't get hot.

[Ronnie]

Unplug the left headlight bulb. Put the hi beams on and see if the wire gets hot.

[Barney Eaton]

After reading your post several times and looking at the service manual, I would check the following......

(1) try the high beams BUT unplug one bulb at a time. See if one headlight bulb is causing more heat buildup than the other.

(2) I would also feel the green wire (high beam) at the headlight to see if there is any heat there.

The above test are to eliminate things.....

(3) I feel like you have a bad headlight switch and while it turns on the lights, it is a bad connection and the heat is building there and transferring to the yellow wire.

[Guest Drake]

I installed Sylvania Silver Stars about seven months ago, to date, no problems.

[Ronnie]

Looks like this might be another one of those threads that ends without anyone knowing what resolved the problem. That makes it really frustrating for anyone who is searching for help on a similar problem in the future and arrives here at a dead end. It would benefit everyone if people seeking and getting help would please report back here what actually corrected their problem.

[D-a-n-i-e-l]

OK guys this is not too hard of a problem and should not end in a no answer found!

It is not the head light type causing the issue. Ir un the silverstar lights and have no problem.

OK what does the yellow wire go to and what is its function?

I will cheack tomarrow after my weekly hair cut, if no one ansewrs me.

next I did not see any mention of a blown fuse. Only two things cause a blown fuse. 1) short to ground. 2) ading too much poopoo to the circuit.

And for the record adding resistance will not burn out a wire or fuse. Although adding arcing will. (remember E=IR or volts=resistance x current). So increased resitance= less watts, wich watts = volts x amps/current so E= amps X 2 x resistance = less E/volts x I/amps= less watts. confused yet?

Any way I will lok at the system tomarow and see what the yellow (burning) wire is, for I am sure it is not as difficult as we would like to make it seem.

[D-a-n-i-e-l]

wyane were are you at?

[D-a-n-i-e-l]

OK here it goes.

Disconnect the head light switch, the headlight door switch, pull the high/low relay, disconnect the headlight door module (found under the relay center) and BCM

1)Mesure resistance of the yellow wire from in back of the switch to the yellow wire on BCM, then to the yellow wire on the headlight door module, and to the yellow wire on the high/low relay.(all should be close to 0 ohms)

2) mesure yellow wire at the headlight switch to yellow with black stripe at the headlight door switch. Measure this in both directions: ie swith your multimeter leads for this is a diode and wire check. (should measure high risistance/ohms or almost open in one direction and low or almost no resistance in the other)

3) Measure the yellow wire at the headlight switch to ground. (it should measure infinate ohms or open)

If every thing thus far is checking out you have no wiring issues.

4) Reconnect the head light switch. Press the high and low buttons, nothing should happen and the yellow wire should not get hot. (if not your switch is bad)

5)connet the BCM and turn on and off the hi and low lights. the ICP should show hallogen lighs on along with high low beam off annd on. If the yellow wire heats up your BCM is bad.

6)Reconnect headlight door module. Turn high/low lights on and off. If the yellow wire heats up the problem is likely the module, but that is not the only option and we will go over that later if the issue is in this part of the cicuit.

7)reconnect the hi/low relay, turn high/low lights on. If the yellow wire heats up your have a bad relay.

8)Reconnect the headlight door switch and turn on lights. If the yellow wire heats up there is an issue with the switch or wire prior to the headlight door switch.

9) Replace found deffective part and go on your marry way.

Let me know what the issue was and if you find it.

[Guest wayne2reattas]

First of all I would like to thank everyone for all the feedback! I did everything mentioned with NO luck! So , I called around to a few automotive electrical repair garages.

The first was eager for me business UNTIL I said it was a Reatta. He then told me he wasn't interested. I called another garage which was recommended to me. He was willing to give me any info I needed but did not want to work on the car. It ended up being the dimmer switch causing all the problems. Wiring only got hot after the high beams were on for a couple minutes. I just put the dimmer switch in this afternoon-so far things appear to be fine.

Once again thanks for all the feedback! It was GREATLY appreciated.

[D-a-n-i-e-l]

That makes sense the BCM grounds the relay throught the dimmer switch, but I di not think it was seperate from the headlight switch. Glad to hear it is fixed.

[Guest wayne2reattas]

Daniel-

Thanks for all the info. I replaced the dimmer switch and things seem to be o.k. If not I am going to go through your list step by step!

I live in Pittsburgh , Pa.

Thanks again for doing the research! I do appreciate all the help I can get!

I have a 88 which I have spent the last 6 months getting right. A couple weeks ago I bought a 89. So I guess I will go through all the issues again. Shouldn't be as bad the second time around. Especially with the help here and Jim Finn an e-mail away for the parts I need.

[Guest Drake]

Wayne, is the dimmer switch you replaced part of the turn signal lever assembly?

[Guest wayne2reattas]

Drake , Not sure if it was or not. I am out of town right now. My son did it the other night. Will let you know as soon as I can find out.

[Guest wayne2reattas]

Drake,

He said it was down on the steering column.

[Guest Drake]

Wayne, thank you!