Outer Limits 4x4 Board

Thanks all for helping sofar with my slightly tempramental Rocky. Now I have the 7.5A Gauge Fuse, supplying instrument illumination, warning lights, Voltmeter and Tacho blowing as soon as IG switch is turned from ON to START and engine fires up. Does not seem to affect any other functions. One can hear the glow plug relay switching (if IG left On - up to 4 times) and one more time the instant motor fires up. Then a surge current of more than 20A blows fuse.
This initially happened on starting in the rain with wipers, lights and vent fan switched on, now occurs everytime.
Service Manual for F75 maybe not too clear on wiring for F78 - Can somebody please enlighten me on the Startup sequence?

Not going outside right now to look on mine cause its cold and dark , but 7.5 amp sounds tiny. I'm sure all the fuses in mine are 15A or above. Have you got the fuse box cover? Is 7.5 A the correct guage fuse?

Thanks RockyF75 - Fuse cover shows it as 7.5A. With IG switched ON, draws 650 mA which increases to +/- 750 mA when glowplug relay activates - guess it's the current drawn by dash indicator as it comes on. Once switched to START and engine fires up, current shoots up to 20A+.

Could be vibration of engine starting up causes short on part of Gauges feed line running into engine bay. I've checked where possible in engine compartement, but I'm not sure what all's supposed to draw current at the instant of startup, so unable to identify and isolate short.

This looks like such a beautifully simple machine, one wonders why Daihatsu (or previous owners) skimped on the quality of electrics or fiddled around because wires and harnass arn't always all properly wrapped and tied. Possibly earlier versions were better made? Anyway for now I plug a spare fuse in just to check fuel gauge etc, then remove it before startup

Just has a quick look in my F75 manual and found the wiring for that fuse. I will assume the F78 is the same.
(page BE-7)

The 7.5 amp Gauge fuse supplies:
4wd lamp
oil pressure lamp
.parking brake lamp
.fuel drain lamp
.glow plug lamp
.seat belt lamp
.brake fail lamp
.temp gauge and sender via relay contacts
.fuel level gauge and sender via relay contacts
.tacho meter
.through the charge fail lamp via a diode to the voltage regulator

Could be something wrong with the following because they are switched in once the engine starts:
.voltage regulator
.temp gauge circuit
.fuel level circuit

If you want I can scan the page (BE-7) in the manual and send it to you.
Just send me a PM if you want it.

Stu

Stu, looking at the list you provided I suspect it blows due to some or other relay switching on. While stationary I bridge the fuse with my Amp meter, which I quickly remove once reading goes above 10A. Noticed after 5 or so Starts in succession, current started to reduce, eventually only spiked above 750mA. Plugged in new fuse and started driving all O.K.
The list indicates maybe an oil pressure or temperature problem. But when driving with vent fan running, set heat full on and onto defrost which caused fuse to blow again. I'll unplug oil pressure and temp senders etc. to verify. Would like to rule out the Tacho but do not know location of it's transducer to check.
Have learned on my '91 Honda not to play around with the wiring since no ways could I improve on it - was locally assembled by Mercedes and great quality. Rocky seems to inspire hands-on, which provides nice confidence boost if you're successful

I would be taking a good hard look at the voltage regualtor / alternator.

Try loading the alternator with headlights, etc rather than the fan and see if you have the same problem.

You can remove the cover on the regulator and check that none of the contacts have welded closed.
I use an electronic regulator in my that seems to be more reliable and generally better allround.

Failling that... just start unpluging things until the problem goes away.

Good luck.

Cheers.

Gratefully problem sorted! Aided by Board Members' help traced the wiring around fusebox and found that when tapping the loom and connector running into central locking control unit, whilst engine runs, causes surge across Gauge fuse terminals.
Engine vibration when engine starts or foot brushing against the loom causes bad connection in control unit connector then causes stray current draw on gauge fuse circuit. Anyway peeled back carpeting and tape in that area, sandwitched the looms inside duct tape and properly stuck them down against the exposed metal side of the footwell. Inserted new 7.5A fuse - Fixed