jackhild59

iTrader: (7)

I have a 15 amp fuse blowing on the ILLUM circuit of the 88 GXL. When I replace the fuse everything works for a time. I wired my trusty ammeter into the circuit and found that the circuit only pulls about 3 amps. All the lights work, they all have equal brightness, there seems to be no corrosion on the terminals of the bulbs etc.

I thought that I would find a burned light switch and harness, but no. I don't detect any heating in the light switch circuit when the lights are on.

Any ideas what is going on or where to look?

Thanks

Jack

HAILERS2

Any chance you could turn the rheostat all the way down for the next couple of days/nights and see if the fuse still blows? That might prove its the side lights causing the problem ..more or less.

You seem to have already looked at the headlight switches elect plug and down in the corner where the White/Green wire is and seen nothing at all peculiar. I'm just guessing it's the switch going out which might take out the short harness later.

There's a achieve article by Icemark that explains how to prevent the problems with burnt out headlight switches/short harness. After my 87 stk turboII short harness burnt up I got a new switch and harness and did what he did but a little bit differently. I just didn't want it to happen again. Ooooops..........I just mispoke in a way. I did not replace the switch because with the Icemark workaround you don't pass much of any current thru the switch other than what a aftermarket relay pulls.

Maybe check the amperage and then turn the switch on/off numerous times to see if you can create a problem????? Or leave the switch on for a long period of time and try to duplicate the problem that way???

Nope. I've no other ideas other than trying to dup the problem. I kinda like the idea of leaving the light switch to ON for an extended period of time. No need for the headlights themselves to be on though.

Got some aftermarket item tied into that circuit?????? Some boomity boom box like device? joking .... I like boomity boom boxes driving down the street in my neighbor hood. Gives me a heads up that their coming down the block so I'll be ready to take a couple of shots at 'em (caled an editorial remark).

HAILERS2

https://www.rx7club.com/2nd-gen-archive-72/heavy-duty-light-switch-operation-how-too-prevent-burnout-164931/

satch

iTrader: (1)

Amperage = volts/resistance. In your case the resistance is increasing and results in the amperage drop. You might want to depin the Red/Black wire which feeds the tail lights and the Red/Green wire that powers various illuminated items and see if the fuse blows. If it does then the problem is not located after the switch.

jackhild59

iTrader: (7)

So I replaced the fuse, everything worked. My last 15 amp fuse.

Turned the switch on and off 15-20 times. No problem. It's 7:45, nearly dark.

Drove the 5 miles to Orielly Otto. No problem with the lights. (102* outside, but I have R152a so the A/C is ice, different thread!) Bought fuses.

Went outside started the car turned on the lights. Fuse is blown. Replaced said fuse.

Drove down the parking lot 200 yards, turned the lights of and on 4-5 times. Good lights. Just one more on/off pop goes the fuse. Hmmm... I made it blow with the switch?

Put in a new fuse, I have lights (great, since it's now dark)

Drove home 5 miles, turned onto my block. Hit a little dip in the road pop goes the fuse.

I feel the housing around the light switch. It feels warm. Aha!

Waiting until Friday/Saturday but gonna put the relay in and do the Icemark mod.

Gotta get this done, since the Kid has his sister's 626 at the University and my 90 Vert is in the HiSkool parking lot with 4000 door bashing Ritalin junkies...

jackhild59

iTrader: (7)

Yeah, I am developing a theory that the problem originates in the switch itself. Something heats up due to increased resistance. A connector (on the harness?) or internal to the switch( and thermally connected to the pin )and that heating causes the burned connector. I have replaced a headlight switch and harness on this car one other time. I cleaned and bulb greased all the sockets, so didn't do the relay trick. I simply couldn't make the circuit pull any amperage, just 3-4 amps.

Regarding the whole restance increases at the bulbs therefore the amperage rises etc etc. Look at the equation (P=EI and all the rearrangements like your variation) If the resistance goes up, the current goes down. Current is expressed in amperage, therefore the circuit would actually use/pull LESS amperage. Thus an increase in resistance in one of those lights could not cause the fuse to blow OR to over tax the circuit in the switch. It HAS to be somthing heating up in that switch or harness.

Maybe it doesn't matter, the relay mod will take the current out of the switch and keep the damage from progressing.

HAILERS2

"dip in the road, pop goes the fuse" .................makes me think there's a short in some plug/harness/wire/somewhere/anywhere in the car where the illumination fuse supplies power to a light bulb.

Reminds me of a inflight electrical problem that couldn't be found during maintanence troubleshooting over a looooog period of time on a F-16. Finally found the problem was in a harness routed along a aft equipment bay door.

When the door was lowered for troubleshooting the "short" could not happen due to the way the harness was routed on the door, but when the door was up and closed, the short could happen if the vibrations etc were right. Usually waaaay up in the air. Actually the harness ran close to the door and contact with the door/harness happened only when the door was closed.

Problems like that are sometimes found by "shaking and massaging harnesses". Or using a TDR which is more or less out of the question and usually only effective if the short is a hard short to gnd.

misterstyx69

iTrader: (142)

doesn't the illumination fuse also involve the park lights?
If so,I'd be checking outside parking lamps(side markers).and their connectors.

jackhild59

iTrader: (7)

Been there done that, see post #6.


My impression was that the whole dash shook, including the pod and the switch. I was able to pop the fuse once turning the switch. I'm guessing the intermittent contact or increased resistance or whatever is in the switch. The pod surrounding the switch was warm, I don't remember whether or not those switches get warm. They shouldn't, should they?

Next step is the relay step. Maybe it will maybe it won't.

In the meantime the little H.S. Ritalin freaks have 5 more days to ding on my paint...

HAILERS2

Anxiously awaiting the results.

I meant to add (read, finally remembered) this about MY switch and relay install: The switch that is presently in the car will not work if installed per stk wiring. You can ohm out the circuit of the switch that sends power from the green/white wire to the red/black and red/green wires and it will ohm out. But if the switch is installed those lights won't come on at all.

BUT using the relay modification the circuit will carry enough current to pull in the new relay............which in turn makes the side lights, tail lights etc come on. So I did save myself some dough by buying a relay and using what would seem to be a corrupt switch if used as stk install.

Just typing. Not looking for a response of any kind. Just FYI.

jackhild59

iTrader: (7)

Ok, the relay is in, the circuit is fully functional. To late to road test it. Tomorrow I will pound on it.

Results to follow.

jackhild59

iTrader: (7)

Very disappointed. The fuse life was no difference with the relay mod.

So I made an executive decision: This car is not worth my time to trace all the wiring on that circuit. But I still want to know if the fuse is blowing due to a dead short or if the fuse is in time overloading and blowing. Why? Because fuses are in place to protect the wiring from excess current. I need some answers.

I started with the same adapter that I used to connect the ammeter. I installed two pairs of 1/4" female spades wired in parallel. I wired a buzzer into one set of connectors. I installed a 15 amp fuse into the other pair. Now, when iffuse blows, the buzzer has the only current path and it screams it's head off. If the fuse does not blow, the buzzer is silent. The adapter is long enough that the contraption is in the passenger seat.

With the test device in place, I idled the car, ran the lights turned the switch on and off 25-30 times. Ran every single accessory in the car. I could not make the fuse blow with the car in the driveway. But when I drove the car, very shortly the fuse blew setting off the buzzer. I blew 5 different fuses. There was not any apparent reason. I still cannot measure anywhere near 15 amps. There is some random transient event that occurs when driving that blows the fuse.

Now, knowing what I know, I placed a 15 amp re-settable circuit breaker in the same test contraption. I drove that little S4 all around town, hi-way, city, cruised, flogged...I did everything. I could not get the breaker to trip. Not one time did the buzzer go off. The breaker is not sensitive enough to trip on the transient that pops the fuse.

Thoughts?

Pele

iTrader: (28)

Circuit breakers usually have a delay, kinda like a slow-blow fuse.
Standard automotive fuses blow IMMEDIATELY when they detect a high current.

I would DEFINITELY look for an intermittent short circuit behind the dashboard...

Instead of a buzzer in your little device you built, I'd use a lightbulb...In normal circumstances, the light bulb will be dim. When the circuit shorts out the bulb will get MUCH brighter.

Bang on the dash... Bang on the harness under the hood. Percussive troubleshooting is the key here.

Pay close attention to where the harness bends or goes through grommets in the firewall.
Also look for where it could get pinched where recent work has been done...

HAILERS2

How about depinning the Red/Green wire in the headlight switches plug then going for a ride in the daytime with the switch to the first position.

No blown fuse means the problem lies there in R/B path and not the R/G path.

And or turn the lights to the first positon and then go massage the harness/plugs in the tail light area and front side light area. Trying to make it blow.

And or turn the rheostat full up/down a number of times.

This problem lies under the catagorey of "better you than me".

satch

iTrader: (1)

Do as he say, do as he say!

Shut up or the Illumination fuse gets it!

jackhild59

iTrader: (7)

I did run the rheostat up and down repeatedly with no affect on the fuse.

The car did get a minor hit in the left rear corner a few months ago. I replaced the tail light with a nice pristine tail light. There was nothing bent around the tail light, the wiring was pristine. the tail light is pretty much plug and play. Next time I get a chance, I will look that bit of wiring over, and shake it a little.


In the meantime, the 15 amp breaker is doing duty in the fuse box and the car is back at the University.

The daughter is back in the 626, so my Vert is no longer hanging out with the HS Ritalin freaks.

I guess I need to get my kid a fire extinguisher...