1986 2.5 automatic. 100% stock

A few days ago while driving home the fusible link for wire that powers almost everything melted and I lost power to everything but the headlights. The wire appears to be white and is a 12 gauge wire that comes from wiring harness and goes to power junction box near the battery. I repaired the link and used my Sun VAT-40 to check amperage on the wire; this is what I found.


With no accessories on and the engine running the wire was flowing 6 amps. With the radio on it would flow 8 amps, add the blinkers and I would be at 10 amps. With the A/C off, but the blower motor on high I was running 32 amps. With the A/C running the amperage through the wire was 48 amps, add in the four way flashers and I was at 49 amps and the wire was very hot to the touch. I was using a 50 amp circuit breaker for temporary circuit protection, while I was doing this. That is obviously too much amperage for the wire. When I remove the wire from the junction block everything, but the headlights (and their motors) lose power.


Is there too much running on this circuit or is something else causing the amperage draw? I haven't done anything to the wiring and it appears intact and original. The A/C was broken for the entire length of time the previous owner had the car so if something was wired wrong he wouldn't have had the problem because he never ran the A/C, so amperage wouldn't have got about 32. I installed a new compressor 500 miles ago and the A/C appears to be working properly.

Is something wired incorrectly or is something drawing too many amps?

Here are the photos of the wire and junction block in question. The wire in question goes to the top post on the junction block and is the wire coming in from the right.

Unless you know specifically what the consumers are at the other end, you can't tell much just from an amperage reading - there are simply too many variables in any car, much less an older car. What you can generally assume is that the system was designed properly, and the issue you're facing is age or damage. The thing to remember when troubleshooting this type of stuff is that amperage will be inversely related to voltage, so the typical cause of excess amp draw is voltage drop across old wires. The quick & dirty approach to testing this is to measure voltage at the end points (things like the ignition coil, AC compressor, flasher relay, etc.) and see where you've got excess voltage drop. Chances are, you'll find either damaged positive wiring or a bad ground associated with the device. To that point, the drop can start right at the top, with the alternator or battery wiring, so obviously check that too. You can also check for bad grounds by testing for positive voltage between the device ground and a good chassis ground - if you get +v, that device is badly grounded.

Do bear in mind that fusible links work by being undersized or, maybe, right sized. A fusible link operates relatively close to its limit at all times - that's the feature that makes it fusible. When the load increases - an amount the rest of the wiring is readily able to take - the fusible link fails and breaks the link. So, by their nature fusible links can get warm or hot. SAE J156a (fusible link) has a temperature rating of 150°C - that's *real* hot to the touch. As long as you're not approaching that you're really fine. But, to be clear, I'm not saying you don't have an issue - you're going to want to do a voltage drop test - but by the same token you may not. You may have just failed the old link from age.

[This message has been edited by thesameguy (edited 06-05-2018).]

The fuse link that failed is on the Battery feed circuit to the fuse box under the dash and the ignition switch on the column.
The highest loads on the fuse box are the cooling fan and the HVAC fan.
It's possible to get an idea of where your problem lies by pulling fuses and watching for you amp load to drop on your test meter.
Corroded contacts in plugs will cause higher amp draw.
Spend some time unplugging and replugging connectors.
Check and clean your grounding points.

Before I tear into it figuring out what is drawing too many amps I would like to know a few things. I don't want to be chasing a problem that isn't there. If the wire should have close to 50 amps I would like to know.

1.) About how much amperage should be going through that wire?

2) What should the amperage draw be on the blower motor?


3.) What should the amperage draw be on the radiator cooling fan?

The Ogre's cave has a page on this subject that is helpful. It is on a very slow server so be patient. Sometimes you can't get there.

Example:

Radiator Fan Motor is rated at 150 Watts and uses 10-11 Amps about 14 Volts normally. But have a mess up ground and now get 10 volt, motor uses 15 amp. Really bad ground? Say 7 volts? Motor uses nearly 21.5 amps! That will blow the motor and/or relay to controls the motor.

/\/\/\ what they said /\/\/\

Example is See my Cave, Electric Motors and read Wire Service too and likely others.
service has list of main grounds around the car, fix/clean them first then check amp draw again.
example Rad Fan is grounded at left "inner fender" near HL assembly and common rust problem.
Fix/clear all grounds in engine bay for same reason. Everything bolted to engine, trans bell, and car needs looking at.
Coat w/ silicon/brake grease. Safe for plastic insulation unlike most oils hate plastic.
Still see high loads then check for bad connectors etc.

check w/ engine etc off. Should pull < 0.5 amps. Just OE radio far < that. (ECM standby power is another FL to same "box.") Anything more look for bad security, old cell phone parts, etc. Many find disused security audio etc still pulling power... PO had cell amp behind P side seat under the carpet but pulled out the rest when I got the car.

Carefully check HL motors... If warm/hot then likely have problem there too. Motor(s) can twitch too and even kill the battery. Unplug them while looking for other problems or fix/clean grounds near them.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

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