'75 Starter/Solenoid Problem

ColoCommando · Jul 25, 2011

The starter on my Mk III suddenly stopped functioning a few days ago. On the previous ride it functioned perfectly fine - a couple of stops and starts with no problem or hesitation. Then, on the next ride a couple of days later, nothing. Pressing the start button produces no typical solenoid relay clack, much less any starter turnover sounds.

The battery tests OK and I can manually start the bike easily. A simple continuity check of the starter shows that there are no opens. The starter is just a couple of years old and was purchased from CNW, so it is not likely to be the component that is failing. I have removed the starter solenoid and tried to test whether or not it is still working. To do so I simply put a 12 volt source (the battery) across the two control terminals (WP and WR on the wiring diagram). I expected to hear the solenoid/relay engage -- the typical clack sound -- but I heard nothing. An inline measurement of the DC volts shows no voltage. Even if the relay was bad/stuck, the voltage through the circuit should still show approximately 12v shouldn't it?

Before I tear into the right switch cluster to check the state of the start button contacts I'd like to see if anyone else has dealt with starter issue like this one and see what steps were taken to figure out the failing component or otherwise resolve the problem. Thanks in advance for any help.

bwolfie · Jul 25, 2011

Sounds like a dead relay. Not an uncommon problem. I remember seing somone here using a NAPA replacment. Much cheaper and stronger than the original.

ColoCommando · Jul 25, 2011

bwolfie said:
Sounds like a dead relay. Not an uncommon problem. I remember seing somone here using a NAPA replacment. Much cheaper and stronger than the original.

I'll search for that thread, thanks for pointing it out. I pulled the starter to test it and, as expected, no problem getting it to spin. I can check the starter switch in the headlight shell, though I really do think that it is time for a starter solenoid replacement.

rick in seattle · Jul 25, 2011

Try exiting the solenoid with respect to its case; that's how it was designed to operate. Either polarity will do. If it operates, measure the contact resistance; should be at the lowest limit of your ohmmeter. If it doesn't operate, or shows a resistance of a few tenths of an ohm, replace it. As I recall, the OEM replacement is nearly 100 bucks. You'll need a replacement capable of passing an initial surge of 300 amps or so; any automotive starter solenoid should do, assuming you can mount it.

lukeya · Jul 26, 2011

I had a recent problem with my Lucas Mini starter relay - the contacts welded themselves shut causing rather a nasty difficulty.

Anyway - one rebuilt starter motor later (HD 4 field coil casing, 4 brushes, and Torrinton B118 and B68 needle bearings) later, I x 19 Amp Hour Battery later and 1 generic chinese starter relay for a Ford F150 (note I am using the Mk 1 battery tray) for $10 from Canadian Tire - hell the thing sure does start properly now!!

Also - upgrade the cabling.

L

jimbo · Aug 13, 2017

lukeya said:
I had a recent problem with my Lucas Mini starter relay - the contacts welded themselves shut causing rather a nasty difficulty.

Anyway - one rebuilt starter motor later (HD 4 field coil casing, 4 brushes, and Torrinton B118 and B68 needle bearings) later, I x 19 Amp Hour Battery later and 1 generic chinese starter relay for a Ford F150 (note I am using the Mk 1 battery tray) for $10 from Canadian Tire - hell the thing sure does start properly now!!

Also - upgrade the cabling.

L

what are the part numbers for the replacement relay ,Napa or otherwise?

GavinJuice · Aug 13, 2017

I brought in mine to Carquest and he said it was out of an old Ford. Exact replacement other than having to file down the ears a bit to get it to fit.

I'll see if it's got a part number on it.

jimbo · Aug 13, 2017

GavinJuice said:
I brought in mine to Carquest and he said it was out of an old Ford. Exact replacement other than having to file down the ears a bit to get it to fit.

I'll see if it's got a part number on it.

Thanks! :mrgreen:

concours · Aug 14, 2017

ColoCommando said:
The starter on my Mk III suddenly stopped functioning a few days ago. On the previous ride it functioned perfectly fine - a couple of stops and starts with no problem or hesitation. Then, on the next ride a couple of days later, nothing. Pressing the start button produces no typical solenoid relay clack, much less any starter turnover sounds.

The battery tests OK and I can manually start the bike easily. A simple continuity check of the starter shows that there are no opens. The starter is just a couple of years old and was purchased from CNW, so it is not likely to be the component that is failing. I have removed the starter solenoid and tried to test whether or not it is still working. To do so I simply put a 12 volt source (the battery) across the two control terminals (WP and WR on the wiring diagram). I expected to hear the solenoid/relay engage -- the typical clack sound -- but I heard nothing. An inline measurement of the DC volts shows no voltage. Even if the relay was bad/stuck, the voltage through the circuit should still show approximately 12v shouldn't it?

Before I tear into the right switch cluster to check the state of the start button contacts I'd like to see if anyone else has dealt with starter issue like this one and see what steps were taken to figure out the failing component or otherwise resolve the problem. Thanks in advance for any help.

Did you provide a ground/earth to complete the coil circuit when testing the relay?

L.A.B. · Aug 14, 2017

concours said:
Did you provide a ground/earth to complete the coil circuit when testing the relay?

This is an old thread (2011).

'75 Starter/Solenoid Problem

ColoCommando

bwolfie

ColoCommando

rick in seattle

lukeya

jimbo

GavinJuice

jimbo

concours

L.A.B.

Moderator

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