lights/power/voltage drops

[Previologist]

Problem getting worse, more frequent no-starts, twice yesterday and twice today. I'm not sure when it blew but I noticed my coolant temp gauge illuminator bulb was dead before my trip. Today I noticed the Power Main relay (90987-02004) in the dash block gets awful hot. Probably all irrelevant but I dread trying to track this down. Nevertheless I'm going to pull the fuse block at the battery and check it real good again, then start trying to test. Seems i have no choice. The auto electric shop in town is booked out 2 weeks, and said they would call me back to schedule an appt but never called. The other place doesn't answer their phone and has dreadful reviews.

[Previologist]

I removed the blower fuse just to see if that had any effect. I still get some very slight and very tolerable dimming, but so far no shut-offs or starting problems. Weather is such that I don't need a blower now anyway, so i will continue the experiment.

i only mention it to jinx myself. If something bad doesn't happen now, I may be on to something.

[samstrader]

I don't have anything to offer but have read this full post and there are a lot of interesting learnings in it. I'm sorry you are having the trouble but reading this is a good learning experience for me. Good luck.

I sure does seem like something is wrong in the blower circuit. You know the wiring was messed with and pulling the fuse reduces the problem. That seems like two things pointing in the same direction but sometimes that doesn't work either.

[John Kaufmann]

... Today I noticed the Power Main relay (90987-02004) in the dash block gets awful hot. Probably all irrelevant but ...

Hot would worry me, but warmer than other two relays of its type would not. The Power Main relay is usually on, enabling power to the power accessories (doors, windows, moon roof). The Fog Lamp relay to its left, and the Engine Oil relay (in the row above, between the Fog Lamp and Power Main relays) are usually not on until their respective control switches are enabled, and so draw no current most of the time. That explains the temperature difference, but if it's too hot to touch, try swapping it with one of the other two and see if the heat stays with the relay or the function.

[Previologist]

previa97.jpg


The MAIN relay gets quite hot, definitely hotter than the other 3 similar (round metal) relays most of the time. The FR-HTR (HI) relay also gets hot when the blower is on.

My FOG slot is empty, but to the left of that is a HORN and then TAIL. The other similar relay is ENGINE OIL LVL which never gets very warm. neither does HORN.

The TAIL also gets hot when the headlights are on, but not quite as hot as the MAIN. I can only keep my finger on the MAIN about 3 seconds when it is at it's hottest, and 8-10 seconds on the TAIL. Interestingly (to me) the MAIN cools off quite a lot when the blower is on. Then it is only warm.

I haven't tried switching it but since the hotness is situational it will likely be the same result. But I'll try it anyway

[isights]

I haven't checked my relays to see how hot they get yet, but when you have resistance, you get heat. The coils in relays will produce some heat as they are energized, but relays should never get so hot you can't touch them. There could be corrosion on the pins for the relay, or the connections of the socket. Or, the relay contacts could be burned and present excessive resistance to the power they are switching. Having lights dim when something else is switched on is a clear sign that your circuit is not able to deliver the current needed to sustain the voltage it should.

Years ago I had a '67 VW that had tail lights that didn't work. The volt meter showed 12 volts at the bulb socket and the bulb tested good. Known good bulbs didn't work either. The fuse looked ok as well. I finally checked the voltage at the across the bulb when the lights were supposed to be on and it was very close to zero. It turned out the fuse element on the old style ceramic fuses VW used for a long time had oxidized and made for a very resistive connection. With no load (bulb removed) I could see 12 volts, but when the load was applied (bulb inserted) the bad connection at the fuse would only let a few electrons pass and the voltage would fall to zero. Electricity was passing through the bulb filament but not enough to get it hot. Cleaning the fuse fixed the issue.

It sounds like you have found the location of your problem, you just have to diagnose exactly what is causing the heat. Where exactly is the connection poor.
I also had Bosch relays with bad solder connections around the pins on the bottom in my 1995 Volvo wagon. A common problem that was solved with reflowing the solder around the pins. That was more of an intermittent issue though.

Keep checking voltages and good luck.

[Previologist]

I switched the OIL LVL and MAIN yesterday, and nothing changed so at least I've definitively ruled out the relay itself. Could still be the connectors I suppose but I will rule that out and think it unlikely.

I also found that the TAIL gets hot even with just the running lights on. Not sure if that tells me I can rule out headlight wiring or not.

Years ago I had a '67 VW .

Grumpy old Fred, is that you?

[John Kaufmann]

I switched the OIL LVL and MAIN yesterday, and nothing changed so at least I've definitively ruled out the relay itself.

Thanks for making that check. I'd say it does rule out the relay; the only difference is that POWER MAIN is normally on, and OIL LVL normally off. I'm surprised the coil draws enough current to get really hot, but that must be the case. I'm regretting (for lots of reasons) the demise of my Prev, or would have just checked it myself (having never noticed that issue when I had it).

Could still be the connectors I suppose but I will rule that out and think it unlikely.

Agreed. IAC you could check that quickly by pulling the POWER MAIN relay, jumpering pins 1-3, and measuring the voltage from that jumper to ground (should be well under a volt), but I would not expect a problem there.

I also found that the TAIL gets hot even with just the running lights on. Not sure if that tells me I can rule out headlight wiring or not.

That's not surprising. In addition to powering the tail lights, the TAIL relay also energizes the DRL relay. Again, it just must be that the relay coil draws more current than we might expect.

Grumpy old Fred, is that you?

Thanks for the reminder of Fred Cisin - who probably could answer your question out of a lifetime of experience.

[man_btc]

Prev,

I may have misread something you said in your very first post, that "I ran a new battery cable from the battery to ground, no change." Did that mean (I assumed) you actually replaced the long cable that runs all the way from the battery negative to the engine near the left engine mount? If not, here's something you may want to try: take one side of a jumper cable (i.e. a wire with the same color clamps at the ends), attach one end to the battery ground post and the other end to a good engine ground, maybe something you can get to under the driver's seat. With that known-good ground in place, see if your dimming goes away. If so, your engine-to-battery ground cable is the problem.

Engine Ground Cable.jpg

[Previologist]

Prev,

I may have misread something you said in your very first post, that "I ran a new battery cable from the battery to ground, no change." Did that mean (I assumed) you actually replaced the long cable that runs all the way from the battery negative to the engine near the left engine mount?

No, alas, I'm not that smart. I just ran it to the nearest bolt in the body.

If not, here's something you may want to try: take one side of a jumper cable (i.e. a wire with the same color clamps at the ends), attach one end to the battery ground post and the other end to a good engine ground, maybe something you can get to under the driver's seat. With that known-good ground in place, see if your dimming goes away. If so, your engine-to-battery ground cable is the problem.

Thank you for posting this because I've been meaning to track down the place where battery ground meets engine and kept forgetting to ask where it is. So I found it now, and found a 1 inch gash in the ground cable a few inches above the end, where it is collecting dust and gunk and exposed to moisture etc.


ground.jpg

But when I ran a jumper from the battery ground to the point this cable attaches (which looks fine and tight), I still had dimming of dash lights with brakes or blower. I then ran the jumper to a couple even cleaner dryer engine points under the seat, and still the dimming of dash lights persist.

I did not disconnect the gashed cable while performing these tests, so I don't know if that matters.

[man_btc]

That break in the ground strap insulation doesn't look serious at all. And when you put the jumper cable in parallel with the ground cable you eliminated it as an electrical path that might be the problem given that the jumper cable should've been able to carry all the current by itself. Once there's a big enough wire to carry all the current required from one point to another, other wires connected along the same path don't make any difference.

[Previologist]

Once there's a big enough wire to carry all the current required from one point to another, other wires connected along the same path don't make any difference.

Sounds like a bunch of Voodoo to me.

But it's probably a good thing I crawled under the van because I noticed another fun problem coming my way: my left front strut appears to be leaking oil. That will definitely have to wait quite some time, because I can't do it until I get home in a few weeks and I can't do it then either because I have to replace the clutch in my 4runner first. Big fun. (not to mention the 4Runner timing belt and valve cover gaskets but those can wait)

I'm going to test my DRL wiring eventually but I'm a bit afraid to crack the plastic or brittle gaskets when I'm so far from my parts van so I may procrastinate that until I get home in April too. @Isights may be on to something and I've been planning to do that since before I left home

[man_btc]

Re: Voodoo and wiring currents

Once your wiring capacity is big enough to carry all the current being drawn by the loads, the only thing that varies with extra wires connecting the same two points is how much of the total each carries. Let's say the jumper cable was the same size wire as the ground cable, and there wasn't anything wrong with the ground cable. In that case 1/2 the total current would flow through each. If you added two extra jumper cables, each of the four wires would then carry 1/4 of the current. Remove all the jumper cables and the (good) ground wire would go back to carrying 100% of the current - but again, the total current would always stay the same.