1982 Coaster voltage drop to ignition switch.

Submitted: Tuesday, Mar 20, 2018 at 16:41
ThreadID: 136452 Views:4579 Replies:6 FollowUps:10
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Hi. I have a 1982 diesel Toyota Coaster which up until today has been fine.Today it appeared there was no power to the ignition switch. Checked battery - 12.84V. Checked connections from battery and all seem fine. Fusible links at battery seem fine. Pulled apart steering column and found only 3.6V getting supplied to ignition switch.Found a box under the passenger side dash, behind fuse panel, that looks like a regulater. There was 12.84V at the centre connection and nothing from other connections. Only things working are horn and headlights. NO tail-lights, stop lights, blinkers, dash lights, wipers.
Any suggestions would be extremely gratefully received before I tear all my hair out.
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Reply By: RMD - Tuesday, Mar 20, 2018 at 16:57

Tuesday, Mar 20, 2018 at 16:57
Don’t trust fusible links, they are made of resistive strands and are designed to fuse, ie burn out, even if they haven’t burned they do sometimes fracture and the resistance increases. (Tug firmly on each one as a physical test. ) That may be limiting current to the ignition.
Maybe test each fusible link with a heavy load, ie, a headlight globe or compressor clipped between the supply and where the FL feeds to. Only do for a short time to either confirm or rule out FL/s as a problem.
Not sure if your is wired similar to Coronas of same vintage, but I had FL burn through inside, looked fine but passed no current. The one which failed/broke inside, was also the alternator charge line ( silly idea) when it blew, it took out the alt reg, the headlights filaments, the radio fuse, electronic ignition and blew a hole in wiper timer IC. High alt voltage was the cause.
Hope you discover something to enable repair.
AnswerID: 617725

Follow Up By: Seto - Tuesday, Mar 20, 2018 at 17:06

Tuesday, Mar 20, 2018 at 17:06
Thanks for the reply. Have metered after the fusible link and I have 12.84V. It appears that the issue is somewhere in the dash as I am getting 12.84V at 1 point in the dash but other than that only 3+V.
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Follow Up By: RMD - Tuesday, Mar 20, 2018 at 17:18

Tuesday, Mar 20, 2018 at 17:18
If just using a meter but no load, even a bit of carbon can show battery voltage to a test point but will not carry any appreciable load. Unless the fusible links are physically checked or load tested it may not show the true picture. Just the first step to elimination I suppose.

PS How many fusible links are there? Usually more than one and they both will be supplying voltage to different places in the loom.
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Follow Up By: Seto - Tuesday, Mar 20, 2018 at 17:49

Tuesday, Mar 20, 2018 at 17:49
Would it be feasible to bypass them, purely as a test, for a moment to help identify if they are at fault? That way if voltage is then good it shows the FL's as faulty.
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Follow Up By: RMD - Tuesday, Mar 20, 2018 at 18:04

Tuesday, Mar 20, 2018 at 18:04
yes, That is why I suggested the large wattage globe or a compressor (swithced on of course) as a higher current passing device but will act as a limiter if there is a short circuit. ie, the globe would glow FULL BRIGHT or the compressor would begin RUNNING.

A compressor or similar load would allow the system to operate or at least try and operate. It should allow the starter circuit to be activated.

For fault finding in fused circuits I have a blown fuse with two heavy wires soldered to the top of the fuse legs. Then I can match a load, ie, a 100w if need be to see if the load globe is simply being shorted to full bright ,ie, Fault present, OR the circuit is running with it's normal resistance of the appliance in series with that load globe and the item will either operate or try to at least.

Just replacing fuses all the time is hit and miss. If fault is not easliy found then it is a miss and another blown globe every time.
FollowupID: 889492

Reply By: HKB Electronics - Tuesday, Mar 20, 2018 at 17:59

Tuesday, Mar 20, 2018 at 17:59
Check for plugs and sockets, in the wiring to the ignition switch, they can overheat and eventually fail.

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AnswerID: 617728

Reply By: Ron N - Tuesday, Mar 20, 2018 at 18:26

Tuesday, Mar 20, 2018 at 18:26
Seto - Your simple old starter/ignition setup should have a heavy wire that runs current from the positive pole on the starter motor, directly to the ignition switch.

This wire should be colour-coded and easy enough to follow through the harness.

I'm pretty sure this wire has a fusible link in it, but they can sometimes be hard to find. Usually they're located in the wire, not far from the starter.
It's certainly worth a light load test on this fusible link to ensure it's still O.K.

As HKB says, connectors are a primary source of problems. The bayonets often become corroded, and refuse to let adequate current through, or stop the current flow altogether.

Follow the heavy ignition wire from the the starter to the ignition switch and see if there's any connectors in the line.
If so, separate them and check the bayonets carefully for corrosion.

I use some CLR dabbed on with a small brush, or a small container of CLR that I can dip the connectors into, to clean them up.

A few minutes in the CLR, then a flush with clean water and a blow dry, and then a spray of CRC 2.26 soon sorts the problem.

I also look for repair work on wires where crimped connectors have been inserted.
Unless soldered, crimped connectors are usually a major source of faulty electrical connections.

Cheers, Ron.
AnswerID: 617731

Follow Up By: Seto - Tuesday, Mar 20, 2018 at 18:40

Tuesday, Mar 20, 2018 at 18:40
Thanks for the suggestions Ron. I am finding numerous connections of twisted wires wrapped in insulating tape. As I find them I am redoing them or if possible replacing the dodgy wire. I have found one fusible link at the battery. According to the wiring diagram I have located there may be 2 others. Now to find them....
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Reply By: Seto - Wednesday, Mar 21, 2018 at 15:06

Wednesday, Mar 21, 2018 at 15:06
Well latest update. Tested and proved Fusible link at the battery. Have removed twisted joints and used proper connectors. No joy yet locating other fusible links. Examined the ignition switch. When the switch is in the OFF or ACC position I am seeing 12+V. As soon as I switch it to the ON position the volts drop straight away. This has been by measuring at the switch terminals. I have also found that there is a momentary 12V when for example switching on the cabin lights(LED's). They come on and as quickly go off.
If I apply power from the Glow Plug Relay behind the fuse panel to the fuses I can get every thing that wasn't working to work.
It's as if there is either a dead short when I switch the ignition to ON or a dodgy Fusible link still somewhere. Has anyone any idea where I may find them?
AnswerID: 617758

Follow Up By: 9900Eagle - Wednesday, Mar 21, 2018 at 15:41

Wednesday, Mar 21, 2018 at 15:41
Although your battery reads 12'8 volts it maybe stuffed and as soon as a load is put on it it drops it's guts. Try turning on your headlights, this will tell you if the battery is us.
FollowupID: 889521

Follow Up By: Seto - Wednesday, Mar 21, 2018 at 16:05

Wednesday, Mar 21, 2018 at 16:05
Good thought. Headlights are fine. Even when I switch in the 2 extra storage batteries there is no improvement.
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Follow Up By: Ron N - Wednesday, Mar 21, 2018 at 16:26

Wednesday, Mar 21, 2018 at 16:26
Seto - In the link below is a Coaster ignition/glow plug circuitry diagram. Unfortunately, it has no date or model listed, but it may assist.

Also, unfortunately, the diagram is half in Japanese, which doesn't help - but it does have a lot of English abbreviations and a few English words, so it can be figured out.

The batteries are in the lower left corner, "ALT" is alternator, "FL" is fusible link (in the wire), "AM1" and "AM2" are typically a slow-blow fusible link fuse, that is in the fuse boxes (Google "Toyota AM1 fuse" for images of what they look like). These AM1 and AM2 fuses are typically 30 or 50 amps.

Ignition switch is in upper left corner (you'll see "IG" for ignition, "ST1" and "ST2" for starter wires, etc, etc.
The wiring marked "M/T" is the manual transmission neutral lockout switch.
The wiring is colour-coded, and the Toyota wire colour codes are as follows;

B = Black, W = White, BR = Brown, L = Blue, V = Violet, SB = Sky Blue, R = Red, G = Green, LG = Light Green, P = Pink, Y = Yellow, GR = Grey, O = Orange.
The first letter is the wire colour, the second letter is the stripe colour. Thus, L-Y indicates a blue wire with a yellow stripe.
A symbol with two arrow darts indicates a male bayonet connector.

Coaster glow plug wiring diagram

Look for dirty or corroded fuse blades or fuse box connectors, half-melted fuses, or pinched wiring where the wiring goes through areas where it can be squashed against sharp metal. This can cause a short circuit or a blown fuse or fusible link.

Cheers, Ron.
FollowupID: 889523

Reply By: Seto - Friday, Mar 23, 2018 at 00:21

Friday, Mar 23, 2018 at 00:21
Well. Don't know exactly how I fixed it. In desperation I pulled out all the fuses to check(all good) and then as I can find no listing of what fuse is what I proceeded to apply power to each individual fuse output side. Got most of them sorted. Then proceeded to replace all the fuses. Turned the key and everything was working. Started without an issue. Can only assume bad fuse contact or dodgy wire at the rear of the fuse block(may have moved it when I pulled the fuse box to get at the back.
Thanks for your input as I worked through all the suggestions before pulling all the fuses.
AnswerID: 617773

Reply By: HKB Electronics - Friday, Mar 23, 2018 at 09:59

Friday, Mar 23, 2018 at 09:59
It is not uncommon for fuse to develop fracture lines, especially the larger rating types, they look ok to look at, not obviously melted but still open, I would look closely at all the suspect fuses especially the ones in the ignition circuit, the 90A AMI and ALT fuses.

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AnswerID: 617778

Follow Up By: Zippo - Friday, Mar 23, 2018 at 11:43

Friday, Mar 23, 2018 at 11:43
and - to the OP - if you are going bush, make sure you have spares (yeah, obvious I know, but not everybody makes sure before leaving).
FollowupID: 889565

Follow Up By: Seto - Friday, Mar 23, 2018 at 18:19

Friday, Mar 23, 2018 at 18:19
Totally agree Zippo. I think I carry enough spares in general to fix a convoy.LOL
Hate to think how much extra weight I am carrying. Spare bulbs (all types), fuses (all types), bolts, nuts, wheel studs, wire, connectors and the list goes on.

Yep HKB will do. My first problem with the fuse box was identifying which was which as there is no cover or markings and it was a different layout to the one in the Toyota workshop manual. Think I have them all sorted now.

FollowupID: 889569

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