High beams on - radio goes off

[JD Cross]

I done several searches but can't find a thread on this.

I recently replaced my original 91 head unit with one from a 95.
On a recent road trip I noticed when I flicked my high beams on, the head unit shut down.
High beams off, head unit comes back on.

Warrenw thinks it may be a sign of weak capacitors in the 95 head unit.
Has anyone else had this problem?

 

[docjohn]

........no but my old alfa would blow a fuse if the wipers were used simultaneously with the aftermarket behr ac....

 

[DocL]

Sounds like you have Lucas electrics in your car with those sort of Gremlins. You may have a very rare NSX.

 

[Old Guy]

Since you are the original owner, I assume that there have been no weirdo electrical repairs or modifications made to the car?

Does the radio only cut out when you flick the high beams for passing or does it also cut out if you switch the high beams on permanently (there are two sort of separate circuits)? Also, when the radio switches off, it is completely switching off or just the lighting that is switching off, or just the audio?

My take is that all of the NSX radios are the same over the production run; but, I don't know that for sure. I have a pin out for the 1991; but, the service manual / wiring diagram for my 2000 is in the trunk of the car which is now in storage so I can't compare the pin outs. I am pretty sure the plug is the same; but, if you can, check the pin out for the 1995 radio to make sure that the wiring arrangement did not change. I don't think that is the problem; but, best to eliminate it as a possibility.

Both the radio and the high beam lighting control are tied into the security control unit. I think; but, am not sure, because the service manual does not provide details, that the security control unit gives a +12v signal to the radio when everything is good. If the radio loses that signal, then it shuts off. Your operation of the high beam may be causing the security unit to do something to the signal to the radio. (Edit - On further checking, I am a little uncertain about this last bit. The service manual says that the wire between the head unit and the SCC is supposed to test out at ground potential. So, I am not clear as to whether the connection causes the SCC to go into alarm when the radio is disconnected or whether the radio needs a permissive from the SCC to operate. Unfortunately, the test procedure has no discussion of the SCC / Head Unit interaction and doesn't list the head unit as one of the alarm triggers.)

In the absence of some more definitive symptoms, I am really doing a lot of guessing! With some more details, I may be able to suggest some simple tests. I don't think that it is a capacitor issue if the head unit operates normally when you are not busy flicking your high beams!

 

[JD Cross]

Since you are the original owner, I assume that there have been no weirdo electrical repairs or modifications made to the car?

Does the radio only cut out when you flick the high beams for passing or does it also cut out if you switch the high beams on permanently (there are two sort of separate circuits)? Also, when the radio switches off, it is completely switching off or just the lighting that is switching off, or just the audio?

My take is that all of the NSX radios are the same over the production run; but, I don't know that for sure. I have a pin out for the 1991; but, the service manual / wiring diagram for my 2000 is in the trunk of the car which is now in storage so I can't compare the pin outs. I am pretty sure the plug is the same; but, if you can, check the pin out for the 1995 radio to make sure that the wiring arrangement did not change. I don't think that is the problem; but, best to eliminate it as a possibility.

Both the radio and the high beam lighting control are tied into the security control unit. I think; but, am not sure, because the service manual does not provide details, that the security control unit gives a +12v signal to the radio when everything is good. If the radio loses that signal, then it shuts off. Your operation of the high beam may be causing the security unit to do something to the signal to the radio. (Edit - On further checking, I am a little uncertain about this last bit. The service manual says that the wire between the head unit and the SCC is supposed to test out at ground potential. So, I am not clear as to whether the connection causes the SCC to go into alarm when the radio is disconnected or whether the radio needs a permissive from the SCC to operate. Unfortunately, the test procedure has no discussion of the SCC / Head Unit interaction and doesn't list the head unit as one of the alarm triggers.)

In the absence of some more definitive symptoms, I am really doing a lot of guessing! With some more details, I may be able to suggest some simple tests. I don't think that it is a capacitor issue if the head unit operates normally when you are not busy flicking your high beams!

Thanks for the guidance.
I'll test the radio/high beam flicking vs high beam on operation today.
I've also just started on doing TSB 93-007 to repair my pass side door lock switch which has been setting the alarm off when it's unlocked.
You may have found a connection here.
I'll be back.

 

[JD Cross]

The radio operates normally on low beam or high beam driving.
It is only interrupted when flicking the high beam lights on.
However of interest is that the display on the head unit changes when flicking the high beams depending on whether the doors are locked or unlocked.
This is suggesting a link between the head unit, high beams, door locks and security unit as mentioned by Old Guy.

First I'm going to repair my door lock switches , then we'll see if the symptom remains or not.

 

[Old Guy]

The radio operates normally on low beam or high beam driving.
It is only interrupted when flicking the high beam lights on.
However of interest is that the display on the head unit changes when flicking the high beams depending on whether the doors are locked or unlocked.
This is suggesting a link between the head unit, high beams, door locks and security unit as mentioned by Old Guy.

First I'm going to repair my door lock switches , then we'll see if the symptom remains or not.

Definitely do the fix as per the TSB. Are you going to try for the out of warranty 'good will':smile: ?

If that doesn't provide the fix, then I agree that checking the operation of the SCU would be a good next step.

 

[JD Cross]

Definitely do the fix as per the TSB. Are you going to try for the out of warranty 'good will':smile: ?

If that doesn't provide the fix, then I agree that checking the operation of the SCU would be a good next step.

I could try for a goodwill fix but I after 24 years I think I might be out of luck. :frown:
I'll report back once I've taken both doors apart and tried to repair the existing switches.

 

[Speedmaster]

Jim - didn't you just replace the head unit with a used one? could that be the culprit here?

 

[JD Cross]

Reporting back after fixing the problem.
Both of my connectors from the switch to the door locks were clogged with some type of grease/sealer from the factory.
It was applied to the topside of two connectors apparently to seal the connectors from any water/moisture coming down from the window etc.
Over time it had melted and seeped inside the connectors and interrupted electrical flow.
I cleaned everything up, resealed the topside of the connectors with silicone seal and zip tied the connector parts together to make sure they were tight.

In any event the car alarm doesn't go off when I unlock the passenger door any more and the radio is fine.
I have no idea why but clean tight connectors seemed to fix it all.

 

[Old Guy]

JD

Just for future use - silicone seal uses acetic acid as the curing agent which is not kind to electrical connections. The silicone seal is probably not going to be a problem; but, there are other sealers and grease like sealing agents that may be a better choice - in the future.

 

[JD Cross]

JD

Just for future use - silicone seal uses acetic acid as the curing agent which is not kind to electrical connections. The silicone seal is probably not going to be a problem; but, there are other sealers and grease like sealing agents that may be a better choice - in the future.

Did not know that and thank you for the info!

 

[GraemeD]

JD

Just for future use - silicone seal uses acetic acid as the curing agent which is not kind to electrical connections. The silicone seal is probably not going to be a problem; but, there are other sealers and grease like sealing agents that may be a better choice - in the future.

Dow Corning 3145 is a mil-spec sealant that is safe for wiring.

 

[Old Guy]

Dow Corning 3145 is a mil-spec sealant that is safe for wiring.

Good point. My recommendation was too all encompassing. 3145 is a moisture cure sealant so it doesn't suffer from the acetic acid problem. I was thinking of the more common silicon sealants available from the chain stores which all tend to be vinegar cure.

As an observation, even conventional silicones are OK on wiring. It is the actual metal terminations and particularly soldered joints that are the problem and the problems may not emerge for a long time. In addition, if the coating is thin enough the acetic acid may not be a problem. However, if you have ready access to 3145, it would be a good choice. Being a moisture cure would not be a problem for JD in Vancouver. Might be a problem for me out here in the land of the dry cold.