1990 12v HZJ75 - Exploring a Hacked Up Wiring Harness (1 Viewer)

[TreadingLight]

I've got an Australian HZJ75 with dual batteries in parallel (12v system). I haven't owned it long but I've known the wiring was suspect since the headlight bulbs were melted when I first picked it up. Lately it has been hard to start even with fully charged batteries, so today I decided to pull it apart and see what I'm be dealing with.

It's quite a rats nest with some ugly custom splices and for some reason, two glow-plug relays? Here's some questions as I go.

1 - What's this thing?
See the image #847 - it's bolted to the firewall and has 4 terminals. 1 is a ground. 2 of them go to each of the battery + terminals. One is suspiciously tapped into the blue/red wire going into the windshield wiper motor (see image #850).

2 - What is this other thing?
See image #848 - this two post device was found inline between the battery + and the switch for the aftermarket offroad lights.

3 - Vacuum switch valve?
See image #853 - it connects to the injection pump and what appears to be the power steering pump? I haven't dug that far yet. Suddently it occurs to me I have no idea how the vacuum system works on the 1HZ.

 

[TreadingLight]

4 - What's this Power Outlet box?
See the image #857 - it's bolted to the firewall just behind the headlight. There is a spliced connection from the battery + going into it.

5 - Why do I have two glow plug relays?
See image #859 - I have both a 28610-54250 and a 28610-57100 under the hood. Both are spliced together and connect to the battery +.

6 - Where is the alternator output?
Can anyone tell me which wire should be carrying the charging current from the alternator to the batteries?

7 - Grounds for the batteries?
Right now the batteries are grounded to the engine at two different points (block and exhaust manifold). Should they have two separate grounds or a common ground?

 

[SKULLYOTA]

1. if it has dual batteries in parallel, then there has to be a relay between them to prevent one from discharging the other, but still allow them to charge simultaneously. If there isn't a fancier battery management device in there, that's probably what its there for. It's just a generic automotive starter relay, and the tap into the wiper harness is just to get a IGN or ACC + to activate the relay while the engine is on.

2. Aftermarket circuit breaker instead of a consumable fuse between the switch and the +.

4. Normal land cruiser component, should have a ground terminal, three fused places to tap power for accessories (i think one for constant power, acc power and ign power)

7. Batteries don't need the exact same ground, block and framerail are the common ones. I've never seen a car with an exhaust manifold ground....it'll work, just a hot spot to attach a cable to. I'd change that one to a frame or block.


That's all I got. Mine's a 24V, but I could see how mine looks as far as the other components you asked about.

 

[SKULLYOTA]

My guess for #3...the 1HZ vacuum pump is what that device is connected to, not the PS pump. I think they mounted right next to each other. I think this is probably the idle-up mechanism for A/C if you have it?

 

[roscoFJ73]

See image #853 - it connects to the injection pump and what appears to be the power steering pump?

Yes, from the Vac pump to speed up the inj pump when the AC comes on. Interchangeable with 6* series from memory.

What's this Power Outlet box?

Stock, its for connecting heavy duty electrical items. All 3 of my 7* series had them. Ive never connected anything to it.

 

[TreadingLight]

That explains the hard starting. The batteries are connected to that relay using small gauge hacked up wiring. I'll be replacing it with a better isolator from my parts box along with the cables.

I need to make sure I put the alternator output on the correct side of the isolator. Any suggestions on how to identify that from the harness?

And why 2 glow plug relays? I am assuming this isn't stock and one of them is a hack job fox or is controlling some loadbi havent found yet.

 

[tlaporte]

Starting in late ‘82, the 2H diesel (and it’s later variants, like the 12HT and, I think, the 1HZ) used a two-stage glow process, which used a pre-heat glow, followed by an “after glow.”

The part numbers you list check out as stock for a 1990 HZJ75-MRQ.

 

[TreadingLight]

Got it - thank you. I'll keep both relays in place. In the last picture of my 2nd post, you can see how the two glow plug relays are spliced to the + lead from the relay. Is that a factory splice? It doesn't look like it but it's reasonably secure so I'm inclined to just tape it back up and forget I saw it.

Now to track down the alternator charge connection. I may have to do that by trial and error unless anyone can point me at the color coding on that cable.

 

[TreadingLight]

I just picked up some lugs, cables and other connectors to put this all back together.

For the two leads carrying current from. The battery to glow plug relays should I fuse them or use some fusible link? Part of me wants to put all this on a small fuse box but maybe that's overkill/overcomplicated. I'm not sure how much current the glow plugs draw.

 

[tlaporte]

There's a wiring diagram at the end of the Factory Service Manual that you can look at.

To my eye looking at the EWD, both of the Glow Plug Relays are protected by a single fusible link, 2.0L, which is 2mm² (light blue).

 

[TreadingLight]

2mm (~sae 12 gauge) is pretty small compared to the cables coming off the relays (8 and 10 gauge) respectively but I know the fusible link is supposed to be smaller.

Is fusible link still the best way to protect a circuit like this? Any sense of the current draw for the glow plugs?

I may be over thinking this but I'm looking to do this once and never dig into the harness again. Not a fan of endless wiring projects.

 

[tlaporte]

There’s a good FAQ here that addresses your questions pretty well.

Are there any general guidelines for choosing a suitable fusible link?
Typically, a given harness segment is protected by fusible link that is four gauge numbers smaller. A 14-gauge wire would be protected by an 18-gauge fusible link. A 6-gauge wire would be protected by a 10-gauge link, and so on. Odd number wire gauge sizes like 19, 15, 13 and 11 are counted when sizing a link. The length of a fusible link should not exceed 9".
​

Also, I liked this question/answer:

What size fusible link should be used in a new installation?
The suitability of a fusible link in a new application can be determined only by a qualified harness engineer with full knowledge of the circuit protection requirements, the installation and operating conditions, and the safety and liability aspects. We cannot make specific recommendations.
​

I figure the Toyota team is far better qualified in this area than I, so in a case like this, I’d stick with the OEM design.

 

[roscoFJ73]

You can buy this for about $30

 

[TreadingLight]

Nice find. I've got a mess of wire and terminals and tools now on my bench so I may build it myself but good to see the option.

Speaking of building it myself, does anyone have a good source for Toyota wiring harness connectors? Or even universal connectors? I can find H4 connectors pretty easily but I'd like to find some 2-pin connectors for things like the corner lights.

In addition to fixing things that are broken, I'm probably going to build a custom harness with relays (for the headlights) and LEDs (for corners/tail/reverse/auxiliary trail lights). Rather than butt splices and tapped wires, I'll make custom lighting harnesses to plug into the stock harness.

 

[TreadingLight]

For those of you in the US, this may be the perfect thing for harness repairs / custom lighting harnesses. I found the link on another thread on mud. I'm not sure yet if they have the stock Toyota connectors for all the lights but I'm going to look through it and see what I can find. I'll get the H4 connectors here for sure.

Automotive Car Truck Light Bulb Connectors Sockets Wiring Harnesses Receptacles

 

[tlaporte]

Nice find. I've got a mess of wire and terminals and tools now on my bench so I may build it myself but good to see the option.

Speaking of building it myself, does anyone have a good source for Toyota wiring harness connectors? Or even universal connectors? I can find H4 connectors pretty easily but I'd like to find some 2-pin connectors for things like the corner lights.

In addition to fixing things that are broken, I'm probably going to build a custom harness with relays (for the headlights) and LEDs (for corners/tail/reverse/auxiliary trail lights). Rather than butt splices and tapped wires, I'll make custom lighting harnesses to plug into the stock harness.

@Coolerman and @RAGINGMATT both carry a multitude of various OEM connectors.

 

[roscoFJ73]

Nice find. I've got a mess of wire and terminals and tools now on my bench so I may build it myself but good to see the option

I have re done the fusible links on a few of mine. I just took the remnant of the wire to a specialty parts shop and they matched up Toyotas wire to theirs.

Speaking of building it myself, does anyone have a good source for Toyota wiring harness connectors?

A lot of electrical components on 7* are identical to 60 and 80 series . Cars as well for the smaller things.
It doesnt answer your question but its often easy to track down bits for local models that will work on yours.

 

[TreadingLight]

I'm still debating putting fusible link back in, vs running them through a fusebox. The glow plugs would need a large fuse but the others would be straight forward.

For now I left the circuits unprotected and ran them off the battery. Everything works and its cranking and starting nicely. Next steps are to figure out what circuits do what so I can sort out what goes on the main vs aux battery.

In other news, I just found some new mystery connectors behind the kick panel on the left-hand side while crawling under the dash. They are dangling, unconnected. I'll post pics as soon as I get my phone to cooperate.

 

[TreadingLight]

dupe

 

[TreadingLight]

dupe